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MG MGB Technical - fuel pump electrical wiring

I have a 73 roadster. The fuel pump failed and I am replacing it. Fuel pump that failed was an after market product that had been retrofited by a previous owner. I purchased and installed a new SU pump from Moss. After installation, I connected the white wire to the spade connector in the middle of the pump, and the black wire to the spade connector on the end of the pump. When I turned the ignition on to start the pump, it did not operate. I went to the back of the car, and there was smoke. Turned the ignition off, and the insulation on the white wire was burnt badly. Three questions: What would cause this? I may have connect the leads backwards, but I did not think this mattered on these new pumps? Will the pump be damaged? What should I do about the wiring? Insulation on the white wire is partly melted right to where it enters the harnes. Black wire is undamaged. Any help appreciated. Thanks.
DJ Shaw

DJ - The pump is not damaged, but you are going to need to replace the white wire from the pump to the fuse block in the engine compartment (and possibly the wires around it in the harness if they were damaged by the overheated white wire). What you did was to hook the white wire (positive voltage) to the ground on the pump. The correct hook up is the white wire to the lug on the power terminal on the end cover of the pump (what you are calling the end of the pump) and the black wire to the lug on the coil housing flange (what you are calling the middle of the pump). Cheers - Dave
David DuBois

If memory serves ...the spade at the end of the pump is the
hot terminal (white wire).

The spade in the middle of the pump is the ground (black wire).

I would test the pump on a bench to be sure that anything
wasn't fried.

Then I would test the white wire with a voltmeter.


Daniel Wong

Thanks alot. Dumb. Hopefully the other wires in the harness are ok. Copper is not melted, just parts of the insulation, so I may get lucky. Would have been nice if the terminals had been marked, but I guess I should have called Moss or posted here to check. Thanks again.
DJ Shaw

And then, either before or while you are replacing the W wire, find the split point at the harness on the firewall just above the starter. Unplug the W wire, get an inline fuse, and install it with two bullet connectors and new connector sleeves.
There are better ways, but this is essential protection.

FRM
FR Millmore

This thread was discussed on 07/05/2011

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