I did a rear battery conversion on my 91 civic hatch. Its a 91 si with a 95 integra gsr motor.
So i did my rear battery conversion with the rear battery wire from a mid 90's bmw. its getting all the power from the battery to the starter. the starter has power. the starter is good. Have tried several on my car and my buddys. no clue whats wrong.
Main relay is good. Only get 4.6 volts at the solenoid when cranking. any ideas?

 

Try new wire, I'd say 2 gauge. Also make sure everything is grounded correctly.

 

Already tried several different grounds. Friend used this same set up and his works fine.

 

check your ignition switch and the main fuse box. the main fuse box supplies voltage to the ignition switch then the ignition switch sends the voltage to the solenoid so if you have voltage at the main fuse box, but not at the solenoid, it has to be somewhere inbetween. i hope that helps

 

You did tap back into the fuse box right?
Using an 8ga wire?

 

Temporarily chain jumper cables together to the starter to make sure your BMW cable isn't at fault.

Try temporarily wiring your battery from the stock location and see if it starts AND then using a different battery in the rear.
Might be the battery.

If you have some 4 or even 8 gauge wire, hook up your battery up as solid as you can in the rear and then run multiple grounds in conjunction to your main ground - see if you can run an extra ground all the way to the block.
It's possible that the seams in your car aren't solid enough to carry the ground.