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MG MGA - Wiring problems

I am in the process or re-building a 1959 MGA. After having everything out of the engine compartment I am in the process of putting everything back. My problem is around the wiring of the regulator (cut out box) and the fuse box. All of the wires have lost any colour code and it is almost impossible to work out which wire goes where. I labeled everything, but some of my labels have fallen off or been painted over. I have been onto Barny Garlords site and got all the relevant diagrams (Thanks to Barny for the most invaluable site on the Net), but without any colour codes on the wires it seems an impossible task. I have considered tracing each wire back to it’s source but that would require that I disconnect all wires associated with the starting or charging circuit to ensure that I don’t get false readings.

As you can see from the motes below, the wires don’t add up, I have no brown on my regulator?

Is there any easy way to trace these wires back, or is it just a painful each wire at a time job after disconnecting everything.

My only other option is to buy a complete new harness, but again how will I work out which cable goes where?



I have worked out the following for the regulator: -

A1 – Brown/Blue – Ignition switch
A – Brown – Starter Switch
F – Yellow Green – Dynamo (F)
D – Yellow – Dynamo (D)
Yellow or White – Ignition warning light
E – Earth

And the following for the fuse box
Description as though I am looking at the fuse box from the front of the car.

A1 (Bottom Right)
Brown – Control Box
A2 (Bottom Left)
Brown/Green - Horn
A3 (Top Right)
White – Coil
White – fuel pump
White – Ignition Switch
A4 (Top Left)
Green – Windscreen Wiper
Green – Petrol Gauge
Green – Flasher Unit
Green Brake Switch.


Garreth Smith
Kent



Garreth

If you were to buy a new harness all the colours would be on the wires so you wouldn't have a problem. With regard to your present problem of being unable to identify the wire core colours it should be a simple exercise to find the relevent other end (eg. brown at starter switch) and meter out the correct wire at the control box. It will take a little time but should be straightforward as you go on.
Bob (robert)

By your description of faded colours I strongly recommend that you do buy a new wiring harness. It will be the best thing you can do to keep your car reliable.
malcolm asquith

Hi Garreth. The wire colout coding often fades over time, so badly that you cant tell which wire goes where. If you dont mind cosmetically "butchering" your harness a bit, perhaps this might work: Strip the cloth or vinyl covering back a few inches on each of the faded wired. Ofen the colour coding IS visible further back, where the covering has protected the wires, and colour coding. Hope this helps. Glenn
Glenn

If the colour has gone, the insulation will be brittle. A new harness is about $150 US, and not only will your job be easier, you will have a much more reliable car.

dominic clancy

Old wires will give you new short circuits,
short circuits will give you break downs,
or worse will give you fires, fires will cause your MGA to burn and for what? to save $150.00 plus your time and labor??? SCRAP the OLD wire harness, BUY A BRAND NEW ONE, remember the trm "SAFETY FAST"
AGAIN your wire harness is over 46 years old YIKES you really are asking for trouble or worse.
BUY A NEW WIRING HARNESS!!!!!!!!!!!!!!!!!!!!!!!
Vic

Garret, I cannot say how much I agree with all the other comments. By all means, if you can, get a complete new harness.

That said, you can work thru your color issues fairly simply. The MGA harness is a fairly simple one and the wiring diagram is easy to read. With some care and a continuity checker ( ohmmeter ) you should be able to determine which wire goes where by working backwards. None of the MGA wiring is split within the harness. Each wire has only two ends. If you are determined to use the old harness, be carefull when "going live". When I replaced my harness, I used a current limited power supply to check all the circuits for function before connecting the battery. Many of the circuits in the MGA are not protected by fuses. An error, or a bad harness, could prove disasterous.

Chuck

Chuck Schaefer

Guys,

Thanks for your advice. It is clear that I should go for a new harness, but I want to get the car running before I introduce more variables. I have replaced the clutch, rebuilt the carburetors, Put a new floor in, welded the chassis, replaced the headlights, replaced the gearbox mounting, replaced the engine mountings and cleaned and painted everything in the engine compartment.

I will need to get hold of one of the companies in the UK that make new harnesses and explain to them about my basket case and get a wiring harness that is as close what I have and want to do. I will be converting her to an alternator and removing the indicator relay. This should make the wiring even simpler than it already is. Even though she is a 1959 Roadster she has 1600 rear lights, an electronic solenoid and an ignition switch with built in starter.

Garreth Smith.
Garreth

So Garret, since you are not shy about updating, will the new loom be braided or PVC?
Dan Barton

Garrett,

Don't hesitate get a new loom.
Even we managed its not too difficult.
You will not enjoy unreliable electrics.

Good luck

David
David Townshend

Now the issue gets clear. To get the engine running you need:

1. Power to the starter solenoid (BIG cable)
2. Power to coil (can take from solenoid battery feed) (goes to SW on coil)
3. Cable between CB on Coil and distributor
4. Power to fuel pump (that is needed to prime and supply the carbs with fuel)
5. If you have an alternator, you need an electrical load on that to avoid damage to it.
6. a switch between terminals on the starter solenoid to activate it.
7. Ground from Battery to chassis

The engine can then be started - no need for a full wiring loom to do that.
dominic clancy

Dominic,

By the time he finishes a band-aid approach, he could have a new harness half-installed.

with an assistant (preferably with smallish hands for tight spots) the new harness is about a day and a half project. That includes prep work like labeling each wire.

Go for it, Garrett!
Joe Cook

Hey, a starter setup as I listed takes 20 minutes to do. If Kent needs to get his engine started, let him tackle the job in his own way (other than trying to rescue a worn out harness that is....).

By the way Kent, a 1600 harness will do most of what you need, and will need mods only for the alternator. I,d also recommend a B wiper motor - it could be that an early B loom is even better for you, and it should fit too.
dominic clancy

Just following on from Dominic's comment - I am currently fitting an MGB 18V engine and four syncro overdrive gearbox into what will be a modified MGA race car and wondered if I will be better off fitting an MGB wiring loom and modifying it to suit the MGA parts, or vice versa, ie. fiting an MGA 1600 loom and modifying that accordingly.

Has anyone any experience of this operation or any helpful comments please.

thanks

Maurice
M. Standish

If it were me I wouldn't bother with a factory loom in a racecar, simply wire the circuits that you need by single cores. Obviously one of the MAIN problems with the MGA wiring is the lack of fused circuits. This is a problem on 2 counts. 1 The lighting circuit is NOT fused at all and therefore any problems here result in the car catching fire. Secondly with no circuit seperation a fault in one circuit takes out a number of others.

With regard to those advising better reliability from a new loom then let me pose this. The loom on my car is one I begged from another enthusiast who bought a new one. I removed all that stupid cotton braid and rewraped it in vulcanising tape. The I cut off all the bullets and soldered on new ones. The loom is in my opinion now better than those new crap things. By the way my friend with his new loom has already had one problem when his fuel pump refused to work due to a bad connector.
Bob (robert)

I agree with Bob, for a racer I would start from scratch and add fuses for each circuit.

However, in due respect for Bob, I do not fully agree with his statement about the questionable reliability of a new loom. In either the case of installing a new loom or the re-use of an original loom, the reliability of the end product is directly related to the skill of the installer. Poor connector attachment ( I assume that this is done by the installer. It was on mine) is not a testimony of a bad loom. And the older looms can be made functional by the use of a rewrap and new terminals as Bob did. The copper wires will survive for many centuries to come. It is their terminations and their insulation that must be evaluated on a case by case basis.

Chuck
Chuck Schaefer

I can't argue with that Chuck seems very fair.
Bob (robert)

This thread was discussed between 27/03/2005 and 31/03/2005

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