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MG MGB Technical - Wiring Problem

I am doing a ground up retro on a 1979 B, the question that I have is in the wiring. I have run the wiring from under the hood back under the car to the trunk, there are two wire dangling from the harness before it enters the trunk one is for the sending unit in the gas tank and the other is for???
I have reviewed my three manuals but I can not find out what this wire is for could some one give me some advice on what it is used for?
Thank You, Andrew
A.A. McFadden

fuel pump? What color is the wire? I believe that the one for the fuel pump is solid white.
Paul Noble

On a 79 the pump electrics would be in the boot/trunk hence I ewould expect those wires to exit the loom there. Earlier tank senders also had a ground wire, but I think that from 76 on all markets had a combined sender and outlet pipe and no ground connection. If it is black see if you have continuity with the bunch of blacks that terminate under the number-plate bolt. If not, the colour will reveal all.
Paul Hunt

Thank you for your comments. I should have detailed my information more than I had. Just to follow up, I have a electronic fuel pump, it is wire up from the wiring loom in the boot. The wire colour is black and has a female spade 1/4" connector attached to it.
Again Thanks
Andrew
A.A. McFadden

Just a guess, but on my 68, the black wire with the female spade is attached to the fuel sending unit as a grounding wire. I'm not sure if your car still needs this.

Cris
Cris

On my 79, a white wire goes from the inertia
switch under the dash to the fuel pump in the
trunk. There is a separate black ground wire
that connects to the fuel pump body in the wheel
well.

The fuel sender unit has a single green (as I recall)
wire connection. The sender grounds via the
locking ring and fuel tank itself.
Ronald

Ronald has a good point. My RB V8 also came with an electronic pump but both +ve and -ve terminals were in the boot on that unit. However the original units had the 12v supply on the end-cap (boot) and ground spade on the body near the diaphragm which is under the rear deck, of course, hence two seperate wires. So it all depends on how the terminals are arranged on Andrews pump as to whether that wire will be superfluous or not.

All this suddenly strikes me with a possible reason as to why my electronic pump was playing up so I put a points-type back in. The points-type has a vent on the body for a plastic tube which terminates in the trunk. This pipe was not used on my pointless pump - no vent - but the pipe was still under there. I'm wondering now whether the pointless pump *did* have a vent somewhere, but because it had no provision for the tube got blocked up with dirt, and the back-pressure was what was stopping the diaphragm from moving its full travel, which was what the problem was. Andrew - if you have a reciprocating pointless pump, something else to check.
Paul Hunt

This thread was discussed between 06/12/2002 and 09/12/2002

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