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Ok I've been done installing a new motor in my car for weeks now and just cant figure out my electrical problem. Its keeping me from starting my car up which is killing me. When I use my multi-tester I have 12 volts at the battery then when I connect the battery to the car it drops down to 8 volts. I've replaced my alternator and starter, I've checked my grounds, searched for pinched wires. I'm running out of ideas and patience at this point. Any one have any other ideas that maybe I'm overlooking? Car is an 04 Mustang Gt and all I did was install a new motor and fuel pump besides that everything else was already in the car before when it was running.

try removing fuses one at a time. and see when it reads 12 volts. that would be you problem circuit

ya thats another thing I've tried and I found one that drops the voltage before I turn the key but as soon as I turn the key the power still drops.

Have you had your battery tested? Just because it reads 12V doesnt mean that it is good you need to load test the battery and check the Amperage. Thats where I'd start, its often overlooked and since you didn't change wire harness etc.., and you have double checked everything else there's not much left to check other than to double check again. I know you said you checked for pinched wires, but I'd check again around the bell and make sure any part of your harness isnt between the block and trans. If the battery is good you almost have to have a short somewhere! Good Luck.

I took the battery out of my brothers car and put it in mine so I know thats good, so I guess im back to checking for a short or pinched wires this weekend.

Did you find the problem yet?

If you know that other battery was definately good and the VDC still dropped then there is definately a problem somewhere.

To isolate this, you need to remove all the car's relays and fuses you can get to. Turn the ignition to the ON position and then install 1 fuse/relay at a time. Caution because some circuits may spark a bit.

For the battery nominal VDC to drop down to 8VDC, there is a serious current pull to do that.

Double check the wiring to your starter.

Also throw a charger on your battery and let it charge for at least 24hours; that way you know your starting with a freshly charged source.

Good luck.

What type of battery cable ends do you have. I've seen the round ones, with a 10mm bolt , stretch enough to not get a good bite on the battery terminal, especially when their used alot. See it you can wiggle it when tight. If so you can either make a shim or replace.