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I recently moved my electric fuel pump from the engine compartment ('74 non tii) to a spot near the tank and installed an inertia switch. All seemed good for a while but then after not running it for a few days, I went to start the car and the battery was dead. After a push start, my multimeter read 14+ V coming to the battery so the alternator output seems correct. I figured I had short somewhere and did the following: Took out the back seat to check I hadn't pinched the old seat belt alarm wire that's still coiled up back there or the old dangling rear window defrost wire or the new wire I had run back to the new pump. All looked good. Then I disconnected the negative terminal from the battery and checked for voltage between the clamp and the battery post. It read 10.5 volts, so there's a short to ground somewhere, right? Next step was to remove fuses one at a time to identify the circuit, thinking if I disconnected the power to the shorted circuit, I'd see the current between battery clamp and post go away. But I still got the same 10.5 reading on all of them, so no help there. Then I cut the new power wire I had just run for the pump thinking I'd find it there. Once again, 10.5 volts, so my problem seems (surprisingly) to be unrelated to the work I just did... I'm thinking I need to start checking unfused circuits but am not sure how to proceed. Anyone have any pointers? Oh, in the middle of this I thought I might just coincidentally have a dead battery, so I took it to o'reilly's - they said it was dead so I replaced it, but that didn't change anything wrt the apparent short. I've left both terminals disconnected for now and can reconnect them to drive the car but I'll need to get this sorted out... 

 

Thanks for any tips,

Phil 

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"10.5 reading"???…… what are you measuring? Amp draw ???? 

 

For reference, an interior light draws about .40 amps +/-. Nominal draw of radio memory/clock, etc usually about .020 amps.

 

I'm working on a customers E30 right now, that was brought in for a current draw issue. Actual fault: alternator and shitty battery cables, hacked by previous "mechanic". I cleaned all the grounds, installed factory battery cables, and an alternator. Everything is fine and dandy now. 12,8VDC at battery, charges at 13.8VDC +/- 

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As above, you should be checking amps between post and cable, not volts. Better to use 10A tester just in case. If you r old battery couldn't produce more than 10.5V after a good charging, I'd say that would be a suspect. How old is /was it? I'd be focusing on current draw from new pump with ignition off. Checking wires for voltage is useful if you're looking a drop in current, which you're not. A short will produce fire works and pop the fuse. I'd do an amp test on new battery before connecting the cable. If minimal amps show, off you go. Otherwise, do fuse test.There are as I recall some non-fused circuits, and I think a bad starter can cause battery drain. But from your description, I'd say the battery chose that moment to expire.

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I checked amperage per Hans and Wegweiser and all looked good, so I hooked up the battery and drove away. All good so far, thanks for the help!

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