I am thinking of redoing the wiring harness on my 78 Camaro. No motor, I was bored so I hooked a jump box to see if anything would light up. I don't know how long this rolling body has sat. Little stuff like the e brake light is on when the e brake is released. One reverse lamp on when the tail lamp is on.

Is it easier to get a wiring harness and what's a good price? Or should I run individual spooled wires, just run a heavier gage to be safe?

 

Those sound like minor issues, and I wouldn't replace the harness for them. I wouldn't run individual wires either. The harness is made up of several pieces, and you can get whatever section is bad replaced. If most the issues are in the rear you can simply fix or replace that portion.
The brake light might not even be the harness, it may be that the switch is stuck, or the brake is not fully releasing and keeping the sw. closed. The reverse lamp may only be a connection touching, or possibly someone put the socket into the wrong hole out back.
I'd just fix things unless the harness is too butchered already.

 

Oh Ok, so I got to do some digging. Good thing I know how to use a multi-meter from my alarm company days. I need to work on resistance though. They thought us how to use it to trace a wire's short in terms of distance, but there was no mathematical formula. You had to test resistance on a wire with the same gauge and strands (if you could find one the same length).
Is the wiring harness under the carpet?

 

Some of the wires run above the rockers under the sill plates (holding the carpet down at the doors), there is another plate under the sill plates and it protects and hides the wires.