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MG MGB GT V8 Factory Originals Technical - Wiring
|Hey, Ive got a 78 MGB with a bored/stroked 215 to about 266. Im going to run one of D&D's GM HEI distributors and I am debating tearing out the old MG wiring harness and going with a GM type wiring harness. Anyone out there gone with something like what Im thinkin about doing? Th reason is the car that I am doing this motor swap into has the original wiring harness and is avsolutely messed up. Someone had the bright idea to use a trailer controller and splice it into the main harness under the dash. Its an absolute debacle. Well, I would appreciate some feedback.|
|Hi, Jarrod, Dan Masters did a nice article on rewiring|
an MGB in the "British V8 Newsletter" Vol.IX, #2
May - August,2001. Check it out at:
|I don't know about replacing with something other than another MGB harness, seems a lot of additional work for something that is going to end up 95% the same as it was before (minus the debacle). I'm in the middle of rewiring a V8 conversion because the loom was chopped about so badly by someone else, and has had a couple of loom fires as a result. This is an EFI conversion, which is obviously quite a bit different from a carburettor conversion. But even so the EFI loom is self-contained and only needs five connections to the rest of the car. The only departures I am making from standard are putting relays and seperate fuses for the (high power) headlights, fused relays for front and rear fogs/spots, and replacing the tubular fuses with blade-type. That and the obviously necessary ones involving ignition and cooling fans.|
I'm afraid I don't understand your reasoning on this.
You say "I don't know about replacing with something other than another MGB harness, seems a lot of additional work for something that is going to end up 95% the same as it was before (minus the debacle).
And then you say "The only departures I am making from standard are putting relays and seperate fuses for the (high power) headlights, fused relays for front and rear fogs/spots, and replacing the tubular fuses with blade-type. That and the obviously necessary ones involving ignition and cooling fans." That is far from 95% the same as original.
It seems to me that if you are going to all that trouble, you'd be much better off making a new harness from scratch. You would eliminate a lot of cutting and splicing, and you could use wire of a larger gauge than stock. You could also eliminate some of the most frequent sources of trouble - connectors. The factory used quick disconnect connectors for ease of assembly on the line - you don't need to do that in your garage. You could also eliminate a lot of un-neccessary wiring, such as the seat belt interlocks, is you are doing a later model.
I also object to the use of fuses in the headlight circuits. It's your car, and you can do what you want to, but MG didn't leave out fuses in these circuits for cost cutting measures - they were left out for safety concerns. It is far better to have a wire harness meltdown than to run off the road into a tree because a momentary short killed your headlights while driving along a windy, twisty, bumpy road at night. Before you say this is something that won't happen, I personally know of two people who have had this happen to them - both driving Japanese cars that do fuse the headlights.
Yes, you can always wire your car very carefully, and maintain the wiring in good condition, but if you can guarantee that you won't ever have a short, then you don't need the fuses anyway.
Making your own harness from scratch isn't for everyone, but for those who have the know-how, a home-brew harness can be a significant improvement over the stock wiring. Especially of there are sigificant changes to the circuitry.
The wiring set-up that Jack mentioned, and that was published in an issue of the V8 newsletter, uses 8 fuses (9 if you add a radio), 6 relays, and the turn signal/hazard flashers, all mounted on one convenient panel. The design is easily customized for individual preferences.
For those that are interested in this, I will be bringing complete kits of parts (all wiring, relays, sockets, fuse holders, etc) for this setup to the 2002 British V8 convention in Michigan in august. I haven't determined pricing yet, but it will be a lot less than the total price of parts given in the article. If there is enough demand, I may even offer completely assembled kits.
|I mostly agree with Dan, but I have gone a bit further on my last 2 conversions, & plan to do the same on the current project. That is to use a GM style harness. I buy a 20-25 fuse/circuit unit pre terminated at the fuse block with colored, printed wires from one of the street rod suppliers. |
There are several reasons for this. First, most of the wiring is 20-30 years old with deteriorating insulation, corroded wires & connectors, & the insulation is not up to modern standards of chemical resistance.
2nd, after re-wiring, everything works better, the wipers are faster, heater blower runs faster, lights are brighter, & when you blow 1 fuse, half the car is not shut down.
Using a pre terminated harness with all the wires labeled is not that difficult to install, except for fiddling with the wiper connections a bit. There are simpler but similar harnesses available with fewer circuits.
A few brand names are Centex, American Autowire, Painless Wiring. A check of the adds in any street rod magizine should give you a few more names.
These harnesses are set up for electric door locks & windows, air conditioning, third brake lights, electric cooling fans, electric gauges, and anything else you would find in a late model car.
A few (or even a lot) of hours spent now on re-wiring can save you many hours of frustration, tow bills, etc, later on.
|Dan - Jarrod wasn't talking about adding individual fuses and relays for the headlights - I was. IMO buying another manufacturers loom and making it fit, or building a complete loom from scratch, to do the same job as the factory loom is making work for the sake of it. The headlight mods I am making simply involve removing the two double bullet connectors from the RH side, extending the two feed wires a few inches back to the relays, the output of which goes to four (two each) fuses, the other side of the fuses going forward to four single connectors (one per filament) where the double connectors were. This is not just 'for the hell of it' but because the owner of the car has fitted high-power headlamp bulbs which currently (pun intended) are drawing all their power through the main lighting switch. A quick test revealed about 10v at the RH headlamp and 9v at the LH. With the new loom and relays I expect to get considerably closer to 12v at both. There about 80 seperate electrical circuits in a 1980 MGB, I am changing two of them, or 2.5%.|
|What I was interested in was seeing if anyone had used a GM style harness. I am planning on replacing the harness as the one in the car now is a mess under the dash and in the rear of the car. I was thinking about using a kit from painless wiring for an early GM car as I dont need the circuits for third brake lamps and electric windows. This will probably be best for my application as I am going to be using an Olds motor, GM style alternator, Auto Meter gauges, and other GM type ancilliaries. Plus, the GM style kits come with good fuse boxes that allow you to fuse just about everything instead of having everything run through 3 or 4 fuses. Jim, have you decided what to use to re wire your conversion? Painless wiring kit?|
|Anyone considering rewiring their car sould check out www.waytekwire.com|
Lots of good stuff.
Dan, a safer way of fusing headlights would be to do what mercedes does. Fuse each light. I think you'll be hard pressed to have both short out. If the Germans think it's safe enough, that's good enough for me.
If anyone wants to spurge, i'd suggest the Delphi Weatherpack connectors. I just got my crimping tools and connectors about a week ago. They are VERY nice. Completely sealed connections.
|Seems like it's all in what you want to end up with. For anything close to stock it's hard to beat the fit and simplicity of the stock harness, and new coupler sleeves and electrolytic grease will take care of all but the most abused connections. An engine swap isn't going to require much deviation from this. OTOH, if an upgrade is in order an aftermarket kit is an easy solution. I will say though that I've never completely trusted crimp connectors, unless they were the mil spec amphenol or cannon plug pins crimped from 4 sides with that darned expensive special crimper. The late MG crimped bullets are in the same class. |
Dan's system is a good solution and gives you most everything you need. It's easily expanded too I believe. No matter what way you go you are almost guaranteed to find you'd like to have just one more wire going to a particular spot. The hand made custom harness can solve that problem but one shouldn't underestimate the degree of difficulty in getting it right. Even using the original for a template it is almost guaranteed it isn't going to fit exactly the same. Space constraints being what they are, I'd shy away from the corrugated coverings, which have to be tape wrapped to keep the dirt out anyway, and I'd only upsize those conductors which will actually see an increase in current.
|I'm rewiring a 1980 car and as far as I can see the bullets are crimped exactly the same as my 73 and 75. I pulled a couple of wires out of the bullets when dismantling. I have also found the lighting wires across the front of the car show oxydisation throughout their length, and this car was off the road for five years or so. I used a small drill to make a conical depression in the open end of the bullets (why are they open if they are crimped and not soldered?) at the front of the car until I could see shiny brass and copper, then filled the depression with solder. Even new bullets had to be cleaned with fine wet-and-dry before the solder would 'wet' them. Also assembled bullets to connectors after applying Vaseline to both beforehand.|
|I'm with Paul Hunt on this one, I would not attempt to fabricate an entire harness for the car. If the original harness is pretty messed up (and even if it isn't, since age is a factor as well), I would buy a brand new OEM harness for the car, then modify it to accept the HEI distributor and other minor changes as needed for the V-8 conversion.|
The 1978 B is late enough that it used lots of multi-pin plastic connectors under the dash for switch and stalk connections. These would be hard to duplicate in a home-brew harness, and it is pure hell to resurrect one of these multi-pin plugs by removing and uncrimping each pin and re-crimping with new wire. Someone will come back and say "well, why not get rid of the connectors and splice the wire together directly". Well, I don't want to cut and resplice 12 wires if my turn signal switch goes south!
I bought an entire new harness from British Wiring in Olympia Fields, Illinois (708-481-9050) for my 1974 BGT V-8. I still had to make a couple of modifications to it to allow for the electronic ignition and the electric fan override switch I installed. This was far easier to do on a new OE style harness than it would have been to build the entire new harness from scratch. Plus, the harness looks factory, not like it came off some hotrod or sand rail or 1990s vintage car.
|I'm using an 21 circuit hot rod kit from E-Z Wiring for my 2.8 Ford conversion. I paid $195 for it. It is reportedly similar to the Painless kit except that the wires are marked with the circuit names but not color coded. |
I am using all Autometer gauges in a custom dash, so that requires a complete new dash harness (not included). The engine uses the Ford Motorsport electronic ignition wich the kit accomodates.
Another major hitch is integrating the steering column controls with the new wiring. If you are planning to add power door locks, antenna, 3rd brake light, window lifts, stereos, etc. these hot rods kits are the best bet. I chose this route because with all the mods I was planning, it seemed useless to pay more for the repro harness and then have to extensively modify it. You also get a modern GM fuseblock with stab-in fuses and circuit breakers. I can't comment on EFI integration as I am using a carb on my engine.
Mercedes uses fuses in the healight circuits because it's the law in Germany. You are trusting your safety to decisions made by politicians. It's interesting to note that Volvo, a car company known for its safety concerns, does not use fuses. Myself, I'd rather trust the engineers in Sweden than the politicians in Germany <G>
I agree, fusing each lamp reduces the chance of losing both lights, but why take a chance at all? Let's think about this a litlle bit more. What would case a fuse to blow? A fuse blows when an energized wire come into contact with ground. When will the headlight wires be energized? When the headlights are on. When will the headlights be on? At night.
What will cause a wire to come into contact with ground? When a wire moves. When will a wire move? When the car is in motion. When will the car be in motion? When you are driving it. So just about the only time you will ever have a fuse blow is exactly at the time you really need your lights. The fuse won't blow when the car is sitting in the driveway, and you normally won't have the lights on when you are working on the car, so the fuse isn't even needed most of the time.
Individual fuse will reduce the chances of failure, but it won't eliminate them. A wire coming into contact with ground is not a problem as long as the insulation is intact, it's only a problem when the insulation has failed. What causes insulation to fail? There are two causes - mechanical abrasion and environmental effects. Mechanical abrasion can occur any time a wire bundle passes through a panel opening or between two mechanical components. The headlight wires in an MG travel together throughout the car, so any source of abrasion for one can also very easily abrade the other. Same for environmental effect - heat, chemicals, age, etc, will affect all of the wires in a bundle, so it's not unreasonable to suspect that both wires could fail at the same time. Last year, while changing the oil in the family sedan, I found three bare wires near the oil filter, one for the pressure switch and two from the alternator. The insulation had cracked from exposure to exhaust heat (I presume, even though the wires weren't all that close to the exhaust manifold) and had completely fallen of the three wires, leaving nothing but bare copper. Luckily, these three wires were spaced far enough apart and far enough from ground in this particular area not to cause a problem.
You might argue that if you keep your wiring well maintained and inspect it regularly, you won't have a problem. This is true, but if you can assure that, then you have no need for fuses.
Luckily, there is a way to have your cake and eat it too. Instead of fuses, use fusible links. Fusible links have the capacity to absorb momentary current overloads, but will blow on sustained overloads. If your headlight wires stay shorted long enough to blow a fusible link, the headlight wires would have burned in two without the links anyway.
OTOH, there are millions of cars on the road, fused and unfused, with only a miniscule number of crashes due to blown fuses or burnt wires, so either way you go, the probablity of disaster is not all that great.
|Paul and Paul,|
I don't disagree with you at all, it would be much easier to simply replace the stock wiring with an OEM replacement harness, especially if you are not making significant chages to the wiring. The further you stray from stock, the more attractive a custom harnes becomes. Rewiring a car from scratch is not for the faint of heart. Replacing the wiring with an aftermarket kit is a lot easier, but still can be a daunting task. Just as the 4-banger that came in these cars is adequate, so is the original wiring. However, this is the V8 forum, and we are not satisfied with merely adequate. I want a 360HP wiring system to match my 360HP engine (that 360HP figure is not wishful thinking, btw, that's been proven on the dyno).
Paul Kile: You said:
"The 1978 B is late enough that it used lots of multi-pin plastic connectors under the dash for switch and stalk connections. These would be hard to duplicate in a home-brew harness, and it is pure hell to resurrect one of these multi-pin plugs by removing and uncrimping each pin and re-crimping with new wire. Someone will come back and say "well, why not get rid of the connectors and splice the wire together directly". Well, I don't want to cut and resplice 12 wires if my turn signal switch goes south!"
I totally disagree with you on this. The multipin connectors are readily available, and very easy to install. In fact, British Wiring sells suitable replacements, maybe even OEM style. Wytek also sells suitable connectors, as do several other vendors. OTOH, why on earth NOT splice the wires together directly? Every connector you eliminate is one potential source of trouble eliminated. How many times do you plan to replace your switches? The ONLY reason any car has connectors is for ease of assembly. On the assembly line, that is critical, but not at home in our own garages. I spent 28 years designing instrumentation, control, and power systems for nuclear power plants, and one of the criteria for good design was the reduction in the number of connectors required (you haven't lived until you've had to justify your designs to the US Nuclear Regulatory Commission). Do yourself a favor, and eliminate every connector you can (especially those #$%#@$ bullet connectors). Leave a little slack in the harness end of the wiring, and you can replace components a few times without any problems - you won't shorten the wires a significant amount by doing this. It takes a little longer to do this than just unpluging and repluging connectors, but if you can't spare that little bit of time, then you probably can't spare the time to own one of these cars anyway (they are, after all, notorious time consumers<G>).
I do agree with you wholeheartedly on the desirablity of the "factory" look, although not necessarily the MG factory. Many of the aftermarket wiring systems use GM OEM fuse blocks, so the wiring would look GM factory original. GM vs MG. Works for me<G>
What do you mean 266?? I believe you were giving a number of us grief for installing small 3.4L (204 ci) 60° V6 motors and saying you were building a 289 ci BOP/R.
OK, 302 guys, chew him up! LOL! :-)
I don't think you need an aftermarket harness or a GM style for your application as my opinion states below, but its a matter of choice.
Mind if i give you grief about using a carburetor? ;-)
A wiring harness is a very important part to any car and should be looked at closely before just hooking every bit and piece back up to it when it has been taken apart. Dieelectric grease and cleaning of the connections on a still good factory harness is all that is generally needed. If the harness has been through severe heat like it has been for Dan, then replacement of wires (or harness) will be needed.
I believe that Lucas has had a worse reputation then it should get. The wiring is fair, 99% of the connectors I pull apart are good, and the systems are comparable to most cars that I have looked at of the era.
The down sides:
*Switches are overloaded and smaller then most swithes
*OEM Generators/Alternators are not producing enough power for modern headlamps/radios and other modern stuff
*Not enough fuses for additional load of most modern items.
*Heck, not enough fuses or wired in for the way most people like modern wiring.
I still prefer using BMC/BL style wiring harnesses for most applications.
By doing this, I am illiminating rewiring of every item in the vehicle and only rewire what is needed. With a V6 or V8 conversion that has a carb and nothing fancy, there should be no problem.
To place relays in the standard system, will save the switches and allow more power to the item in question.
Placing a modern alternator on a car equiped otherwise can be done using the standard harness as well.
Add (what? all of two.) in line fuses where ever you need them on a conversion with carburetion.
The biggest deal is adding relays to the setup with fuses on one side to keep the switchs from burning out and not providing the power flow- and once again, this can be done with a stock harness... No rewiring of your tail lamps because you have added an alternator and a GM HEI setup!
I'm not bashing those who have.. Its all part of the customizing of your car, but unless you have the electric windows, locks, AC, and most of the other options, it probably not worth it.
When I rebuild harnesses for the GM 3.4L Sequential port fuel injected motors with Distributorless ignition system, we still use the stock MG harness. In order to run the motors, we alter the GM engine harness and add it to the standard MG harness which has all the relays and fuses in that section seperately... The way most systems are setup nowdays, with two or three fuse boxes per car! Check most of your modern domestic (US Built) cars- one box under hood, one in the side of the dash or under the drivers feet. If you use a Painless wiring or any other body harness, you would still have to build a harness for the motor.
What ever direction a person takes, to do a harness properly will take lots of time. No question about it.
|Brian Mc Cullough|
Good comments, but I still take issue with your stance on connectors. You asked how often I plan to replace my switches. Unfortunately, that is not a planned event, Lucas quality dictates that I maintain the option of unplugging them. I think we can agree that the stalk and rocker switches used in late MGBs are not built to the standards required by the Nuclear Regulatory Commission. I have had several of those stalk switches fail in various ways over the years, the most spectacular was when the high beam circuit overheated one night and caused a little "candle flame" to emerge from the top of the switch cowl. In cases like that, I would much prefer being able to unplug the switch rather than cut and splice in another one. I hate lying on my back under the dash with a soldering iron!
On the other hand, I don't mind the slight increase in unreliability that the plethora of bullet connectors adds to my British cars. I like the fun of tracking down the odd malfunction if it crops up, and don't mind the time it takes, but I would hate taking that extra time to cut and resplice in a new stalk switch - especially if I had eliminated the connectors in the first place!
And as for the OEM harness look being factory original GM instead of MG - that gives me the willies! I hate General Motors and everything they stand for, so I would have a psychological aversion to making my wiring look GM in my MG! I even have to try to ignore the fact that my GT V-8 engine was originally a GM design! My only consolation there is that GM unceremoniously dropped the design after 1964 (because the American public was too stupid to properly care for the cooling systems, GM was too penurious to keep the engine in production, and everybody wanted BIGGER V-8s!).
|Hi, All, FWIW on my 4.6L 1979 MGB I'm using a Painless Wiring kit in conjunction with VDO gages. It will be a|
while before I get to the wiring portion of my conversion so I can't comment on the installation.
Also FWIW, I just now came in from the garage from doing the final testing on one of my wiring systems (an improved version of the one in the newsletter), which will be shipped up to Fast Cars, Inc, in Wayland, MI tomorrow. Ted and Steve will be installing it in one of their customer's cars, so you might want to pop over and check it out. Anyone else in the Grand Rapids area that's interested might also want to have a look at it. Feedback appreciated.
|I now understand that Dan's strenuous defence of using his new loom is because he is intending to sell them.|
Shouldn't you be putting this in the classifieds, Dan?
|What I mean by 266 was an Olds 215 block with a 300 Buick crank and Chevy 327 Rods with Vega pistons. Real kick in the butt. That is the motor I am putting in to the B. About 10.5:1 compression but I am choosing the lower ratio combination so I can run pump gas. I believe I am gonna go ahead and rewire the B with a GM style harness and throw some GM weatherpack connectors at it. I love those connectors and had them on my Rodeo. Beats all connectors out there. And by the way Brian, it is a 266 if I go .030" over instead of punchin her all the way out to .060". If I get my hands on a 4 bolt main Rover block a little later on, I will then look into goin all the way out to 5.0 with those fancy Brit big valve heads but thats a good rebuild and a large amount of money from here. You wanted a 6 but Ill stick with the 8. Nothin beats the grunt of a well built 8|
You obviously don't know me, or you'd know better than that. People who know me, know I don't operate that way. You also obviously didn't really read what I wrote. If you had, you couldn't have come to the conclusion you did. To suggest that I posted my comments for the purpose of selling my wiring system is absolutely ludicrous. The comments I made apply to ANY wiring setup - stock, aftermarket, or mine.
I published a complete, detailed, set of plans for building this system in an issue of the British V8 Newsletter, and I have mailed out numerous copies of the article to people at my own cost. Anyone who wants to can build one themself, without purchasing anything at all from me. My invitation to check it out in Michigan was as much - or more - for those who may want to build their own as for those who may want to buy from me. The only reason, the ONLY reason, I'm doing this at all is because a significant number of people have asked me to. It was only with a great deal of reluctance that I agreed to do it. I have much better uses for my time from a personal standpoint. I have projects of my own that I'd like to spend more time on. Trust me, I'm not doing this for profit. The odds are VERY high that I'll actually take a loss on this before it's over. Even if I should make a profit, the hourly return on my time will be less than I could make flipping burgers somewhere, a LOT less.
I do things like this because that's the way I am. I like to help people. Comments like yours make me wonder why I bother.
Thanks for your efforts, with the newsletter and all the associated projects. Most of us realize that profit is your last motivation for doing any of it. It's hard not to let a few negative types get you down, but rest assured that most of us do appreciate how much time you spend on things like this.
|I think Steve from CA should buy a harness from "Dan the Evil Capitalist Wiring Harness Czar",see if he can shape it into a noose and let us know how it works out...|
Thank you for the article in the newsletter and the info you have given in this post. I am up in the air as to replace mine entirely or do it a piece at a time. I am doing a 2.3 turbo install on mine right now (ok, not while I am typing) and want to change a lot of things, but want to get my stand alone comp/inj harness working before i do anything else. Please e-mail me with the specs of your kit along with price.
|Dan misunderstandings often happen on the internet when people speak in haste. I appreciate all the unpaid time you have devoted to MGs and TR6. I have your TR6 book and it is a great help. Your efforts are appreciated.|
It's understood that you did indeed speak in haste. Perhaps you had a bad day, or were venting some completely unrelated frustration. Psychologists call it "internet rage". Retrospectively, one may even be shocked by one's own comments, as I'm sure I will be with this this one. Surely you realize that Dan's OK and dosn't deserve such random bashing. Relax. We all have frustrations and such acts of random venting, especially on the defenseless, can be executed by the sweetest people. Well, second sweetest anyway... Hurt feelings beget hurt feelings and before you know it, your reading some 'touchy-feely' dribble from some faceless self proclaimed counsellor who can't type fast and has little better to do than pollute the threads with a bunch of nauseating dribble! If one approaches communications with the "I'm OK; You're OK" philosophy, tensions can be averted and we all benefit from the greater quality of shared thought in an atmosphere of positivity without hurt feelings nor people like me droning on and on endlessly about flawes in the human socio-emotional condition and how we should just all hold hands and dance in a circle.
|Whew!! For a second there I thought he was going to say "...hold hands and dance naked in an octagon."|
I dunno, dancing naked in an octagon sort of reminds me of my college days!
We had a British Car Society in Davis, California, where we would regularly offer sacrifices to the great God MOWOG. Everyone knew that after you finished working on your car, you had to cross wrenches over the bonnet and chant incantations to ensure that MOWOG would grant you another few days of malfunction-free motoring.
We even had plans for a short film, based on the opening scenes from "2001-A Space Odyssey". A bunch of us, clad only in loincloths, long hair, and scraggly beards, would come shambling into view carrying various British car implements (large hammers, crowbars, mainshafts from old Spridget trannys, etc). We had the skeletal rusted remains of an old 1938 Austin 8 that we had set up on the lawn. The motley crew would approach this hulk as if it were the Monolith from 2001, screaming, hooting, grunting, then gingerly reaching out and touching it. Suddenly the ethereal music would reach a crescendo as we are imbued with the Archival Knowledge! We peer down at the tools in our hands, and suddenly know what they are used for! One of us tosses a large open end wrench into the air...the Future of British Car Enthusiasm is born!!!
This thread was discussed between 18/03/2002 and 29/03/2002
This thread is from the archive. The Live MG MGB GT V8 Factory Originals Technical BBS is active now.