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MG MGB Technical - Installing new wireing harness

I am in the process of restoring my 1964 MGB. I have decided to install a new wireing harness. I have no idea where to start. There has to be a "best way" to do this. I appreciate any help someone might can give.
Jim Walton

Jim. A copy of Lindsay Porter's "MGB Purchase and Restoration Guide" will cover this and many other projects you will deal with over the years. Basic theory is to cut connections, leaving them attached to the various connections, so you can see what color wire needs to go where. Great idea in theory. On my 79, the wiring is so "creative" that this system will not work. I got the wiring diagram duplicated and enlarged and work from that. The Porter book, this forum, beer and a relaxed attitude are the key things necessary to replace the wiring harness. Les
Les Bengtson

Hey Jim - I just wanted to let you know you're not alone. I'm expecting the harness for my '72 B any day now. When I got the car, almost none of the wiring was hooked up and the harness had been spliced into in quite a few places. I figured there would be no better time to nip the electrical problems in the bud. As Les suggested, I went down to my local copy shop and had the diagram enlarged and laminated. I've got the erasable markers, the relaxed attitude, and a few free weekends. The beer I'll save for after each day's work; I have a feeling the project is going to be challenging enough as it is! I'd also be happy to hear anyone's suggestions...
Brian LaVoie

I did my 68 a few years ago. I found that most of the attachments were obvious, but others were not. Inside the dash was the trickiest, due to reach. Most of the wires can be attached with the dash loose, about 6 inches away from its mounting surface. Leave either the speedo out and attach it last, as this gives you one more access to reach behind with. I had painted the entire car, so it was over a year between removal and reassembly, so I forgot that the rear sub-harness is installed from the trunk first then the thicker part is threaded through the opening by the rear shock and stretched forward from there to the main harness. I too had such modifications on the original that many wires were seemingly extra. What saved the day was my acquisition of a parts car, same year. Although it was essentially gutted, it had all the dash connections, and all the fasteners were displayed. Better than any book! Whenever, I was uncertain, I had a nice visual in the other car. This helped when routing was in doubt.
Check www.britishwiring.com for some really nice products. Their page and catalog looks plain, but I was very pleased with their harness. The cloth weave pattern is right, and the wires are good. They sell connectors for everything and these are not cheap knock-offs. My headlamp pig-tails were better than original. Much superior to what some suppliers are selling.
-yes, patience is required, and a cool day, too. Sweaty hands make it hard when behind the dashboard blindly screwing the mounting flange down on the back of the oil pressure gauge and the speedo cable and 6 other wires are rendering all but the middle and index fingers useless.
Tom
Thomas Lennon

Just done this on an 1980, a 64 should be relatively easy as it has much fewer circuits. Not covered in my Porter other than 'remove all the bullet connectors before pulling out the old loom' which seems pretty obvious.

The bullets are only crimped on (unlike the spades which are spot-welded) and can pull off as well as corrode internally. With all the lighting bullets at the front of the car drill a conical depression in the end so it shows both shiny brass from the bullet and shiny copper from the wire, and fill the depression with solder making sure you get the bullet hot enough for the solder to run, but not so hot as to damage the insulation. A high-power iron used briefly is best. Make sure the outside of the bullet is clean (no flux) and shiny after soldering. Do this to the wires from the lights too.

Split a length of thin cable sheathing or tubing up one side and put it over the edges of the two holes that go through the firewall to avoid damaging the loom tape or cloth as you work the new one through.

Pull the old one back into the cabin and vice-versa with the new.

Tape the wires that come out of the new loom in the engine compartment to the thinnest part of the loom. If you leave them free you will end up having to pull a greater thickness through the firewall than you need, although yours should be relatively thin anyway.

Use all new bullet connectors (particularly at the front) and put Vaseline inside them and on the bullets before assembling acts as a lubricant (no sniggering please) as well as protection against moisture. Make sure both bullets are pushed home inside the connector, and ends of bullets or the end of the metal connector are not poking out of the insulating sleeve.

The body/boot loom can be a real pain, unless damaged leave it alone.

The main rear and front parking/flasher lighting units do not have ground wires but rely on the mechanical fixings. Consider adding ground wires from these to nearby ground bullet connectors (may need to go to the number plate bolt at the rear of a 64).

If you have any additional wiring do not rely on crimp connections alone, they simply are not good enough. Get the semi-insulated spade terminals that allow you to solder after crimping, using heat-shrink to cover the whole connector afterwards. Do not use those tubular crimp wire extenders as they cannot be soldered at all. Use a male and a female spade, soldered as well as crimped, assemble with Vaseline and put heat-shrink over the lot. Crimp-type bullets do not fit the original bullet connectors without distorting them.

And yes, getting that oil gauge reconnected is a real pain, but remember to reconnect it before you start the engine!

Before reconnecting the battery for the first time make sure everything else is connected as you think it should be, and turn everything off, including any interior and boot/trunk lights. Connect the thick starter cable to the battery but not the ground strap. Connect a meter set to display 12v between the battery ground post and the car body. If it shows 12v some circuit is drawing power (if you have an alternator you should see a few volts, this is OK). I also had an old headlamp bulb with two flying leads, if this lights up at full brightness when used in place of the meter you have a full short to ground from somewhere. Don't reconnect the battery ground strap until you are sure there are no shorts.
Paul Hunt

Mine is the 1980 B which Paul re-wired - a beautiful job too.
We upgraded it slightly using blade fuse holders, a second fusebox inside the car to connect in any extras and also relays on headlights. Ask Paul to go through it. I think that it was well worth the trouble for a clean reliable safer and more modern system which could only be a credit to an original car rather than a modification.
Marc

Last week I went to Fayetteville, NC to take care of some banking business. When I finished
we had lunch and went to the mall on the other side of the and I saw a Barnes & Noble book
store, bad news for my pocketbook. I went in and one automotive book I purchased is an HP
Books "Automotive Electrical Handbook". It doesn't mention MG but it has a section on electrical
theory in easy to read and understand text. It also explains how all automotive electrical parts
and systems work. It has sections on how to make diagrams, how to make a wiring harness,
how to install a wiring harness. I consider it to be a very wothy addition to my automotive library.
Using this book may answer some questions we always rely on Paul Hunt to answer. Cover price
is $17.95 US. So I would suggest getting a copy of this book if you plan to rewire a car and have
little experience. Regards, Clifton
Clifton Gordon

Jim, The first thing to do is to take the wiring diagram to Kindo's and have it blown up. I did this and it help greatly. Also get a good ohmmeter and some extra wire. I got some clips from Radio Shack to create a long wire to check with. Make sure that wire long enough to go from the back to the front. Take your time and double check all of your circuits with the ohmmeter before you hook up the battery. You should have a list of all the electrical components that match the schematics that you have. Go down the list one at a time and verify that they are hooked up correctly. Once that you did that you will be able to reconnect the batter with confidence. This site has a great electrical trouble-shooting page. Use it. Get a folder to keep track of all your paperwork.
Follow all of the advise from Paul Hunt as well.
You should be ok.
Steve
Steve Bourgeois

"Using this book may answer some questions we always rely on Paul Hunt to answer"

Damn, redundant.
Paul Hunt

two words ... Painless Wiring. The kit comes with 18 circuits, wires with the destination printed along the entire lenght of the wire and instructions.

The wiring on my 76B was just replaced using a kit from Painless. Added a Delco 80amp alternator.

The lights are bright, the turn signals work, the fans (cooling and heating) are turning at the intended speeds and the charging system is working fine.

Goodbye Lucas

rn
RN Lipow

I get so tired of this. Lucas electrics overall are as good as any. There darned easy to trouble shoot. The colour system is great. 99% of the time it's because of the person who did not know what they were doing who worked on it before you!!! Now lets see red hooks to black, Hmmmmmm. Any way like I always say. How many thirty year old flashlights (torchs) do you have that you don't have to hit to get them to come on???? Bob I'll stick with Lucas Thompson
Bob Thompson

This thread was discussed between 27/04/2002 and 04/05/2002

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