Problems with Lights, Lamps, and Indicators

Problem: I purchased a kit for my 69 Camaro and I have hit a snag. I have scoured your Technical Headquarters site and have followed the suggestions related to the orange wire (the park lamp/dash feed) and I’ve produced predictable results. When I replace the parking lights fuse, I have 12 volts of power on the orange wire. When I turn on the lights, the side markers light up for a moment and then cut off, producing a blown fuse.
This led me to search for shorts on the brown parking lamp wire. I found a few “suspect” connections in the trunk and repaired them, tried again and it blew the fuse. Short still not found. However, I did notice that when I step on the brake pedal, the brake lights work yet my turn signals in the dash light up. Any idea what’s going on there?
The other symptoms include: no dash lights, no side markers, no parking lights, no courtesy lights – yet the dome light works fine.

You have several problems that all sound installation oriented. The turn signal indicators lighting up is a ground backfeed. The brake and turn circuits have nothing to to do with the orange wire that feeds the brown parking/taillamp wires. The turns and brake lights should function independently if all else is OK (the exception would be an internally shorted 1157 bulb). The only thing that will blow a fuse as you describe is a dead short to ground. The way to find that short is put a fuse in the park light location (the reason you have no side markers, park, or tails is because that parking lamp fuse is blown – all the same feed), then disconnect the rear body harness and pull the lights switch out to the on position. If the fuse holds, your short is on one of the brown wires in the rear body, or even internally inside of a bulb. If it blows again, plug the rear body back in and disconnect the front light harness from the firewall and pull out the headlight switch to on again. If the fuse holds, the short is in the front end. If if blows, there is an issue inside the dash or the headlight switch itself.

Found the short in the trunk – it was the license plate lamp.
So now I have a new problem:  When I turn the key on (motor and headlights off), the blinkers work. But, when I turn on the headlights, the blinkers stop blinking and just light up – no blinking. The hazards do not work at all, no matter the combination. I also do not have reverse lights – but is that because the engine is not running? Lastly, I have dome lights but no courtesy lights.
Your parking lamp housings are not grounded. The brown P/L wire is acting as a ground when the turns are on, but when you hit them with voltage, that wire can no longer act as a feed.  The ground actually is supposed to come from the housing itself being grounded. If you have new 2 stage paint on the car, that is the culprit most likely. Ground those housings well and that will solve that problem. As far as the courtesies, pull the “T” shaped connection apart and you will find that the white wire has folded down against the housing and is not making a ground inside that connection. The orange wire should have 12 volts on it at all times.