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MG MGB Technical - Just getting started

Hello all,

I am the proud owner of a 1978 MGB, I recently bought. I had owned a 1976 before, so I know somewhat about MGs.

From what I have read (found) so far, there seems to be some problems with the electrical system on later model MGs. My car is no exception.

The iginition (on mine) has been 'bypassed' (from a previous owner) with a toggle and a button. Also, some of the dash board buttons dont work.

I would like to start with replacing and rewiring my dash board. I am sure there are wiring harness that I could buy and a new dash should run bout $200..?

Can anyone tell me the 'gotchas' for a job like this? What am I getting my self into? What is the difficulty level (1-10 being the hardest)?

Any help you can give is greatly appreciated.

Todd C


Todd C

Hi Todd

In my experience the wiring doesn't usually give problems except at the point where connections are made.

the exceptions (again in my experience) are :

1) if the well-known gearlever-mounted overdrive switch wiring short problem has fried part of the loom.
PLEASE do the fuse mod !.

2) the insulation on the wires that get close to the engine (and hence get hot) sometimes cracks.
(eg distributor and temperature sender wires)

3) someone has welded close to the wiring.

It is not unusual for various bullet connectors and the fuse box connections to cause problems.

In your position I think I would methodically work my way through the various circuits and sort any probs one at a time, putting things back to standard as you go; simply replacing the loom might not solve all (or any !) of the faults.

HTH.. Don
Don

Don't know how bad your dashboard is or the wiring, but i'd start small first. Get a good wiring diagram, a good workshop manual, and a multi-meter.
You need to figure out why it was bypassed in the first place. Do you have a key, is there a switch there? If the is and no key, you need to remove it and get a key made. If it's there you need to test the switch and see if it works.
I'd start there and get that right first. There are wiring harness's available, but the quality varies, I'm sure someone can tell you the better ones. Some have the coloring wrong and I've heard of new connectors falling off. If it's not too badly mangled I'd try to repair what's there. There are several reasons some switches might not work and I'd tackle them one by one.
If the dash is butchered too and you are going to replace it anyway, you might as well redo the wiring too, as you have to remove all the electronics and once it's off it's really easy to get to the wiring. You can get a dash harness and not have to get into the rest of the harness.
Overall that would take a couple days. You just have to be slow and label everything as it comes apart. Be prepared to trouble shoot for a while once you get it back together. Word of warning is there is an unfused circuit in B's. I think it's brown. Used for radio, wiper, and heater I think. I'm sure there are detailed instructions in the archives.
John A

Agree with Don -- Two days spent replacing all connetors and cleaning all grounding points will eliminate most, if not all, of electrical problems.

Invest in a new fuse box. There has been much discussion on the soder/crimp connectors -- if your use crimp, invest in the proper crimp tool, (see Radio Shack catalog)

That often chastized lucas = prince of darkness -- is more failure to keep oil in the lamp -- meaning, don't let the electrics go to hell by way of no maintenance.

for what it's worth -
glg

Welcome back to MGs. I love mine and it had a few problems when I got it. Usually that is why someone sells a car, any car. Wiring problems are described above. I repaired all mine by simply cleaning all connections and applying dialube. Problems solved. Try it before you assume that the problem is a big one. Enjoy your B.
kids1

Personally, I would refuse to spend countless hours checking every circuit with a tester and stringing new wirs, putting in new connectors, etc. I'd just replace the ancient wiring with a new wiring loom so that I'd know that what I've got is reliable. Click on this: http://www.britishwiring.com/
Steve S.

If you decide to replace the under dash harness try looking at Moss Motors http://www.mossmotors.com/ or British Wiring http://www.britishwiring.com/ It is not hard but requires time and planning. After installing the new harness several people have fried their new wiring by hooking up the battery and trying it out. Get a battery charger that has a circuit breaker built-in and use it to apply power to the wires. If there is a short the charger will pop the breaker and save your wires. As already stated before there are unfused circuits in the wiring.

Wiring diagrams, cleaning all connectors, checking and cleaning ground points, and lastly checking all circuits with a multi-meter will help. The original wiring was pretty good. There are only three areas that cause trouble: corrosion at the bullet connectors, corrosion at the grounds, and lose connections at the fuse box.
Jim Lema

Thanks for all your posts. I am surprised that there are that many people willing to offer help. Looks like I found the right BB.

I AM planning on replacing the dashboard anyway, but it sounds like I dont neccessarily have to change the wiring harness. I will try the little things first and see if I can get it all working. A lot of the switches are cracked and brittle.

I do have an ignition key and will see if I can tell if thats working (great suggestion John).

By "using a battery charger with a built in circuit breaker", I assume you meant to disconnect the battery and then hook up the charger wires directly to the MGs Pos and Neg wires. Then look at the chargers warning lights to indicate a bad connection. Is that right?

Finally, I have seen a lot of shop manuals out there. Is there one that 'rises to the top' (good diagrams/complete)?

Guess Im off to look for some dialube, a multi-meter and a cold one...


Thanks again

Todd C
TCC Todd Canfield

Hi Todd

A good place for diagrams is right here...

Click 'electrical help' on the message board.

Don
Don

Todd,

The Haynes manual is very good, and has decent wiring diagrams. The Bentley manual is more detailed. (Both are still available retail.) If you find a Chilton's or Motor's manual for a good price you can use it for a wheel chock. (The Bentley is also known as "Complete Official Mgb: Model Years 1975-1980.")

Someone else on this BBS recommends taking the wiring diagram to a copy service (e.g. Kinko's) and having it enlarged to poster-sized proportions. Given the project you're about to undertake, that sounds like a good idea.

If it's not a color diagram, I think I'd invest in several different colored highlighters. Not that you'll color the entire thing, but you might want to highlight a circuit, and it would be nifty to do so in the same color as the actual wire.

Best wishes on the project.

Matt Kulka

Todd,
The lock is held on by shear bolts, and maybe thats why they bypassed it. Anyway, if you need to remove it you can get it off using a cutting disk and cut a groove in the bolts. You can then use a flat-head screwdriver to unscrew it. The switch seperates from the lock and you can check it once apart. If you need a new one, i'd take it to a british car parts store as I believe there are several used over the years.
As for the dash replacement, I'd fix all the wiring problems first. It's a fairly involved job with lots to potentially go wrong. That way your not wondering if it's a new or old problem when you try to fix the electrics later on.
John A

Todd:

Here's the link.

http://www.mgcars.org.uk/electrical/

Lot's of very useful information.
Boris

This thread was discussed between 29/09/2003 and 01/10/2003

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.