in my 89 formula when i bought it there was no radio harness connector, just cut wires, so i got a harness from an '87 bird and patched that in, but i ended up with 3 extra wires? all of the speaker wires are connected properly and when i connect the stock radio i hear static, but the display does not light up, and when i connect an aftermarket headunit nothing happens at all. is there a way i can just directly connect the headunit to the battery with another fuse rather than going through the whole harness?

 

yeah, get some wire and splice into the back of the fusebox. Splice in after the fuse, not before it so it is fused.

But you have 12Volts somewhere because you get one unit to power up. Doublecheck your wiring first. Basic headunit wiring: there should be +12Volts all the time to one wire, +12Volts only when the key is on to another, ground, then all the speaker wires.