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MG MGA - Wiring Harness, Help!!

I have a brand new wiring harness and I don not have the foggiest friggin' idea how to begin. There are 5 sections of the harness and no indications of what goes where. This is my first restoration so please help a rookie out.
gerard hutchinson

Gerard,

This is the place to start. Barney Gaylord's website, as usual:

http://www.mgaguru.com/mgtech/electric/et100a.htm

This web page and the following pages should set you right.


Mick
Mick Anderson

Gerard
I was in the same boat as you and was scared to death of rewiring my Mga Coupe. After all the hard work of preparing the car I did not want it to go up in flames due to my lousy electrical work.
I was saved, when a friend loaned me a copy of his Chicago Mg car Club "A-ANTICS" tips book. In it was a step by step wiring description that allowed me to sucessfully wire my car with only one minor mistake. The description is a wire by wiring ....colour by colour ......junction by junction description of your wiring harness and where all the wires go. It starts by descibing the back tail light connection and then proceeeds all the way along to engine compartment ...front headlight harness and under the dash wiring. It is done in plain simple language and following it I got most of the connections in place in one afternoons work.

So do yourself a favour and track down a copy of this article. You will be very happy you did.
Gordon
Gordon Harrison

I have just put a new harness in my 1500 and, like you, I didn't have much of a clue to start with, but I managed to figure it all out by laying out all 5 sections on my bedroom floor and matching the colours to the wiring diagram in the workshop manual. BUT I've now got a problem which I hope you haven't got - my car is an early 1500, with a direction indicator relay unit etc, but I've got separate rear brake and indicator lights ( a la 1600), which means that the rear harness I've got won't do the job! Can anybody tell me how I can overcome this problem?
Robert

Robert Sinclair

Yes. Compare two diagrams here:
http://mgaguru.com/mgtech/electric/circ_f2.htm
http://mgaguru.com/mgtech/electric/circ_f3.htm

If you have a 1500 main harness with the relay connections, it will have White/Purple for left brake and turn signal and White/Brown for right brake and turn signal.

If you have a 1600 rear harness it will have Green/Red for lext turn signal and Green/White for right turn signal. Plug these two wires into the 1500 combo brake light and turn signal fixtures in place of the White/Purple and White/Browh wires. Be sure you use the bright filament for the brake and signal, and the dimmer filament for the tail light.

Where the rear harness meets the side harness connect Green/Red to White/Purple and connect Green/White to White/Brown. Leave Green/Purple disconnected in teh rear harness, as tehre is no separate brake circuit for the 1500 car.

If perchance you also have the 1600 side harness, the colors in the 1600 side harness will match the colors in the 1600 rear harness, there will be one extra whire in the side harness as well, and the mismatched color connections mentioned above will connect up front near the starter switch.

Furthermore, if you have both the 1600 side and rear harness, you can use the extra Green/Purple wire to connect from the brake light switch (Green/Purple connector near starter switch) to a third brake light.
Barney Gaylord

Gerard, I replaced my harness this season and this process worked for me.

I started with the dash harness. Working from left to right, removing the old and attaching the new. Unbolting the dash and leaning it forward was necessary, as was a good diagram.

When the dash harness was in I tested all the switches. When I was sure the dash harness was OK I did the main harness from the dash to only the ignition connections in the engine bay. I taped off the light & horn connections so that they wouldn't short. I tested the ignition to make sure I had the connections correct. Then on to the lights, horn, fuel pump & sender.

This way I was able to work on one group of circuits at a time rather than gutting the whole system at once. This helped me develop the confidence to do the job.

Brian Denis
Brian Denis

Barney,

If you would like, I labelled all the wires on the green MGAs harness we installed and set them out for a photo op. These are the ones behind the dashboard off the main harness. I may have even more then that. This is for the 1500cc cars circa 1957.

I could send you a copy if you would like them for your site.

-BMC.
BMC Brian McCullough

Okay, send photo. It may compliment my CAD drawing of the dash wiring.
Barney Gaylord

I think the book Gordon was talking about is the NAMGAR publication not a Chicago MG Club publication
ie http://www.mgcars.org.uk/michiganrowdies/ttip-book.htm
Barney may be able to confirm.
Mike
Mike Ellsmore

Mikw,
You are right ....that is exactly the book I used. I always thought it was from The Chichago Car Club. Oh well. But I still stand by my remarks. Installing the wiring harness in my Coupe was a "pleasure' using the info included in that book. Then to complete everything...my turn signal problem was fixed with barneys help.
thanks for the correction. Gordon
Gordon Harrison

I have a new harness ready to fit to my 1500. Using the color chart on Barney's site, I have labeled every wire end using a ptouch labeler. It took a while but I am hoping the replacement will now be a breeze.

Dan
Dan Barton

The book in discussion is "A-Antics Tech Tips" from the Michican Rowdies (Michigan chapter of NAMGAR). The NAMGAR national organization had nothing to do with production of this book, which was first available in 1983. I have a third Edition copy from 1991. It was advertised on the NAMGAR web site for a while, until it was deleted when they started selling their own tech book.

"A-Antics Tech Tips" is once again available from the Michigan Rowdies in third edition reprint. http://www.mgcars.org.uk/michiganrowdies/ttip-book.htm

This book does have an article 4-1/2 pages x 2 columns detailing the wiring harness installation. Being a late 1980's production, most of the illustrations are either hand sketches or black photo copy from B&W photos. This book was originally 'the' definitive work on MGA tech information, and it is still damn good reading.
Barney Gaylord

The secret is to concentrate on one component at a time. I used recipe cards and wrote down the wire colours and the terminals they attached to for any component that was confusing or had more that a couple of connections, ie: the Turn signal relay box. Rather than having to refer to the wiring diagram and translate wire colour numbers to actual wire colours I had it on my card ready to go without confusion.
Work on one component at a time and don't get overwhelmed by the big picture. follow a logical sequence of work and take your time.
I have just finished the engine compartment wiring on my car and hope to have the dash mostly done by the new year.

Cheers,
Rich
Rich McKIe

I just finished wiring my 1600 a few months ago. My wiring harness also came in pieces with no instructions. Barney's site was invaluable.
To determine which harness goes where find the colour coded wires for the head light left and right and the brake lights. You then have identified two pieces of wiring harness. The coloured coded wires to the fuel pump and oil pressure switch identify the harness heading to the back.
Use Barney's dash wiring diagram to identify which harness is the upper dash wiring harness. The main harness is the big one with the big "Y".
When I wired the dash I used two 8 inch long brakets to hold the dash off the scuttle and just sat on a crate & very easily wired in the instruments and switches.
I fould that once started the wiring went smoothly.
I didn't label any of the wires as I printed off coloured copies of Barney's drawings and kept the manual open beside me as well.
If you purchased a British Wiring harness you will find serious problems using the bullets, connectors & light bulb holders. They dont fit. You can contact me if you would like to know how to work around the problems. Luckily I saved my old harness and was able to reuse the bullets connectors and light bulb holders.
I also soldered all the bullets as the wires were loose in the bullets.
Good luck
Morris
M. E. WADDS

Gerard,

Maybe some of my pictures can help.

http://s83.photobucket.com/albums/j307/wbetzel/MGA%201600/Wiring/

I think you have to copy this link into your browser to make it work. Good Luck.

Happy New Year and best wishes to you all!

Wim Betzel.
Wim Betzel

Gerard, - Nice pictures. Would it be okay if I include a few of those pictures in my article on installation of the wiring harness? (See 2nd message above).
Barney Gaylord

Barney,

If you maen my pictures it would be my pleasure.

Wim.
Wim Betzel

Thanks. See here: http://mgaguru.com/mgtech/electric/et100a.htm

If anyone else has clear photos of MGA harness installation, I would like to post a complete set on this web page.
Barney Gaylord

OK!! I got the 'A-antics' instructions and began labeling my harness. At the end of section L I still had 2 small sections of harness left. one seems to be an extension with 8 wires and bullet ends on each end. the other with wires on each end and in the middle. can anyone give me a clue?
gerard hutchinson

It should be simple to find by comparing the wire colours to your wiring diagram.

Rich
Rich McKIe

sounds like the wiring for the rear lights. What color are the wires?
Joe Cook

Thanks for the article and all the advice!!! it was very helpful.

However, the article only describes 3 sections of harness and I have 5 and the wiring description was incomplete. The author did indicate that he had to complete the wiring job with spare wires. How does the authors makeshift wiring relate to the additional sections I have?
gerard hutchinson

You will have
1. a dash loom,
2. a loom that goes from by the starter motor to above the fuel sender
3. A loom that goes from above the fuel sender to the rear lights
4. A pair of headlamp pigtails


Lay everything out on the floor.

The thickest cable of all is the one that goes through the bulkhead behind the heater. The main spaghetti is the dash loom.

The longest piece is loom 2 that goes down the right side of the car

The other major piece has the wiring for the front lamps and the coil.

Get a print out of the wiring diagram, and a highlighter marker, a pen and some masking tape. Then start with a test meter to identify the wires one by one on the loom against the wiring diagram. As you identify each one, mark it off on the diagram, and make a label with teh masking tape and tag each wire in turn. The test meter is to make sure that you have identified both ends. The basic colour scheme is Black is earth, green is power, white is ignition, blue and red wires are lighting.

It all looks very daunting at first, but by taking it one step at a time, the unidentified bits become identifiable by a process of elimination of all other possibilities.

Whatever you do, make sure you do this on the floor in a warm, well lit room, doing it near the car will make the process a great deal more frustrating (and longer)

You CAN do it!
dominic clancy

Thanks Dominic, I have already labeled 85% of the wires but ran out of tape.

My final (hopefully) question is... How do I run/attach the harness to the car/chassis? It seems intuitive but I am afraid to rely on my intuition as it relates to this specific task.
gerard hutchinson

There are steel loops that attach with screws to tabs on the chassis, or to other strategic points on the car. They may well still be (partly) there.
dominic clancy

This thread was discussed between 28/12/2006 and 10/01/2007

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