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MG MGB Technical - Wiring questions

Hello,

I am having a few issues installing a new wiring loom to my mgb roadster. As I inherited the car as an unfinished project i didn't have the benefit of stripping out the old wiring loom, hence the questions:

1. I have purchased a 2 piece wiring loom, where do the two looms meet, in the engine bay?

2. Secondly, I have what i believe to be the correct wiring diagram, and whilst this tells me which wires go to the various components, it isn't always obvious which wire connects where. Is there an easy way of working this out?

many thanks,
Alex Davies

Hi Alex you are correct both looms meet in the engine bay driver’s side near the fuse box. I have just fitted a new rear loom in my 69B Roadster, I was lucky because the old loom was still there. I purchased a vinyl tape covered cheaper loom and sleeved it in heat shrink for extra protection. It would save you lots of stress and time if you invested in Rick Astleys MGB electrical systems manual. I found this invaluable and use it allot. To know what goes where you will need a wire colour chart a good website to get wire colours according to the age of your car is www.mgb-stuff.org.uk you should find the correct colour chart on there. I only have the one for my MGB. Also Google ‘MGB Wiring pdf’ and select images and up will come proper wiring diagrams. You can get most of what you need free on the Interweb depends how web savvy you are. All the best
Dave MGB

Alex - Go to http://www.advanceautowire.com/ click on Stock Schematics, then MGB and find the year of your car at the bottom of the diagrams that are presented there. These diagrams are simplified and colorized, making it easier to follow. Use these diagrams in conjunction with the diagrams in the shop manuals (that have a better representation of the routing of the loom), will make it much easier for you to get everything routed properly. Cheers - Dave
David DuBois

Thanks for your help, I've been on autowire and found it useful.

An example of the issues i am having is that the tank unit has 2 connections, and I know that the two wires which should connect to it. My problem is that i don't know which connection is which. Can I do any harm if I was to connect them wrongly? Will the component just not work?
Alex Davies

Hi Alex,

The two wires that go to the fuel gauge are GREEN/BLACK and BLACK. The BLACK goes to the lug welded to the metal plate, whilst the GREEN?BLACK goes to the insulated lug. Connecting them the other way may damage the fuel gauge, as it could be directly connected to chassis, via a spurious connection through the sender locking ring. See photo.

Herb


Herb Adler

You don't mention the year of the car but usually *three* harnesses meet in the engine bay - the main harness from inside the car (many wires), the rear harness from under the car (several wires), and the gearbox harness (only three or four wires).

Most of the wires in the two smaller harnesses connect to the same colour in the main harness. The exception is the green/purple wire in the gearbox harness, that connects to the same coloured wire in the rear harness, for the reversing lights. There can be an exception (colour-wise) involving the overdrive circuit, and there can be two reds in the rear and main harnesses, but that depends on the year of the car.
PaulH Solihull

This thread was discussed between 16/01/2011 and 18/01/2011

MG MGB Technical index

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