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MG MGB Technical - Fuel Pump issue

Holy Cow! In error, I put the white fuel pump lead on the ground terminal! The smoke got out of the wiring harness. To my amazement, the fuse never opened. What values should the fuses be? How much current does the ful pump draw? Tom, 73B

Tom - Unless someone put an in line fuse in the power lead to the fuel pump, there is no fuse to be blown, just the wire and it blows at a considerably higher amperage than any fuse would (and after all the smoke has escaped). If you want to install an in line fuse when you replace the burned wire, go with a standard 10 amp fuse. That will protect the wire and handle any normal current that the pump might draw (generally from about 3.5 - 5.5 amps depending on the pump). Cheers - Dave
David DuBois

Thanks Dave, I am replacing the rear harness and will fuse the pump! What a mess I made! Regards, Tom

As Dave says the fuel pump was never fused from the factory. Both my MGBs came to me with damaged wiring from a pump short, so I have fused mine. The best place to install it is where the wire from the main harness joins the white in the rear harness, in the mass by the fusebox. Use an in-line with bullets both sides and you don't have to cut into existing wiring. Personally I have used a standard 17amp rated 35amp fuse as it is protecting the wiring and not the pump and that rating is perfectly adequate for the pump wiring as it is for the rest of the fused circuits, and you have (or should have) two spares of that rating in the fusebox.

I've also fused my ODs for the same reason, this time where the wire from the main harness joins the yellow in the gearbox harness (although late-model North American spec cars are a little different) in the same area. This had an unexpected side-benefit one day when I had a major float valve leak. I was able to cross-connect the two fuses and use the OD switch to turn the fuel pump on and off as required!
Paul Hunt

This thread was discussed between 21/02/2009 and 22/02/2009

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