Car shorts out when click starter
 

I installed a rebuilt engine in the car and when I turn the key to spin the starter the whole car shorts out and I have to reconnect the battery to reset it. everything is the same from the last time the car ran. Its not the battery it has a brand new battery and I've tried multiple known good battery's. I've gotten it to crank once the only difference is that when it cranked the oil pressure sender wasn't connected. I got the starter tested at my local AutoZone and he said it didn't have enough voltage going through it but it spun. I know there was mice in the car at one point in-between now and the last time the car ran but I inspected everything and nothing looked chewed except the rubber cap on the alternator. My car is a 1986 Rx7 Gxl with a turbo 2 transmission and starter.

I would start with grounds. It's easy to forget them when the engine is removed and reinstalled.

There should be one big one on the starter mounting bolt, and one big on the driver's shock tower towards the bottom. Those are the main suspects.

After that there are several smaller ones that are likely not related to the starter, but still important. Top of the engine / intake has the ECU ground (single ring terminal), and there's a small one that runs engine block to firewall.

Make sure all of these are installed and clean.

EDIT: Oh, and don't accidentally swap the two wires for the starter. You probably already know this from removing and reinstalling, but the starter has two very thick wires. One is +12V, one is GND. It is difficult to mix them up due to length and shape of the terminal, but it CAN be done. Make sure not to or you could start a fire.

classic symptom of the battery terminals not being good enough; clean, tighten

Clean the oil off of your starter.