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MG MGB Technical - White Wire Connections

Hi All
I have an electrical question.
I am sorting out the wiring on a 74.5 MGB electrical system which has been extensively modified, but I think the question is sort of basic.

Here goes.
In the wiring harness under the steering wheel is a multi connector which has 2 white wires joined together via a single connector pin. This is on the female side of the multi connector. (looks like a factory connection)
The corresponding male side of the multi connector is empty.
So the female connector appears only to be a receptacle for joining the wires. One of these wires goes to the ignition switch and the other goes over to the passenger side which branchs off to feed several different items.

There is another white wire under the steering wheel which is connected to the ignition warning light and goes to over to a ignition relay which was added a couple of years ago to solve another problem.

This white wire is connected by bullet connectors. What I would like to do is to wire in the white wire from the ignition light to the male side of the multi connector. This would then plug into the factory? joined white wires on the female side of the multi connector.

And to get even more basic, does it really matter where the white wires join together? As long as they are all white?

Sorry for my lack of proper terminology and I hope I have explained this properly.

Thanks

Bruce
(MGBV8)














MGBV81

What problem are you trying to solve?

The multi-connectors are used to join either the column switches or the dash to the main harness. As such all dash wires should be connected to the same side of its set of multi-plugs, likewise all column switches, and all harness wires to the other side. If this isn't the case you have to start cutting wires to remove either dash or switches from the car.

There should be a single white on one side of one of the column multi-plugs feeding the overdrive and wiper switch. That white comes in the main harness from one of the dash multi-plugs (which has another white in the same pin), and the other half of *that* connection in the multi-plug *should* be going to the ignition warning light on your car.

If an ignition relay has been installed then presumably the original white ignition circuit has already been split into two (one feeding the relay to operate it and the other *from* the relay feeding various ignition-powered circuits, and there were already two separate white systems on that era of MGB, the other feeding the fuel pump from the inertia switch, so now you have three. The other thing to consider is why the ignition warning light white might have been moved in the first place.

When the factory first installed an ignition relay the ignition switch fed that and the warning light, and the relay fed everything else, as that was the most logical and convenient way of doing things. The problem was that current through the warning light from the alternator when the ignition was switched off with the engine running was sufficient to keep the ignition relay operated, so the engine kept running! On American cars this was never noticed as the anti-runon system stops the engine (until there is a problem with the emissions plumbing), but on UK cars without the American emissions systems it was noticed immediately so the wiring was modified. Originally the UK warning light wire was moved to the relay contacts so it could no longer keep the relay operated. However they then had problems with the relays sticking on for other (mechanical) reasons, which kept the ignition, fuel pump, heated rear window and everything else powered, which obviously flattened the battery as well as being a fire risk. So the factory did another mod to move circuits like these back to the ignition switch, and only things like brake lights, wipers and indicators were left on the relay - all a bit pointless in fitting a relay to take the load of the 'biggest' things.

If you move your ignition warning light wire, so it ends up being on the ignition switch and winding side of the ignition relay, then you could well find yourself being unable to turn off the engine.
Paul Hunt 2010

Paul
I am cleaning up the wiring and was going to remove what I though was a redundant wire. But after taking another look at it and your comments I'll just leave it alone. 'IF it ain't broke, don't fix it'!

Thanks for the information about the relay/car not shutting off. Interesting

Bruce
MGBV81

This thread was discussed between 01/07/2010 and 03/07/2010

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