Rear lights, different elements lit
 

Just put in a new electrical system from American Autowire. When i turn on the rear lights the opposite elements are being used. Drivers side front element, passenger side back element and really bright. Ran a heavy gauge wire from box to frame.

Re: Rear lights, different elements lit
 

Am I correct in assuming (from your username) that this is for a '65 truck? And is it a stepside or fleetside bed?

On the fleetside wiring, the rear light contact assemblies (that are part of the wiring harness) fit into the back of the light housing / socket assemblies and are held in place by a couple of protruding pins on either side (very similar to the way the bulbs go into the sockets). I know the pins on the 1157 bulbs are offset so they can only be inserted one way. But I can't remember if the pins on the wiring harness contact assemblies are offset like that too or not. If they're not, it's possible that you inserted the one on the passenger side 180 degrees out of position so now the contact for the tail light is powering the brighter brake light filament and vice versa. If that's the case, simply take that contact assembly back out of the socket, rotate it 180 degrees, and put it back in.