Electrical problem!

[6camaro9]

So i just recently rewired my car with a painless wiring harness. Everything went together easy and seemed to be trouble free until this evening. I put power to the system and everything seemed ok until I tried to start the car. As soon as the solenoid on the starter kicks in and everything goes dead. So at first I thought it was a bad starter. Start checking voltages and had 12 volts at the starter but only 3 volts at the fuse where it goes into the car. After I unhooked the leads going into the car it goes back to 12 volts. I put a new wiring harness on the dse dash also. Could i have a ground inside or a bare cable touching something. Please help.

Richard