Hi hoping people still frequent tis forum, been a while. Always helpful here.
67 Firebird, updated all electrical 2 years ago (American Autowire) Everything was working great.
Noticed my rear tail lights were out, but Brake and Blinker work perfect.
The Fuse for "Parking Lights" is blown, and blows instantly when turning on the lights.

So how do I find the Short? It coiuld be in the Switch, or any of the light sockets, but all wires and sockets are new.

I've read aboiut tricky ways to find a short, I have a test cable made up, base on someone's design, aligator clips on each end of a pair of wires about 20ft long.

Any tips on finding where this short might be? I've got a new boxes of 10amp fuses coming today.

Any help appreciated.

Thanks

Take the bulbs out and probe each socket and find which one is shorted to ground. Could also disconnect the connector that feeds the back of the car and isolate if its in the front or rear harness.

How would I know if a socket is shorted. Can I do it with resistance ? I can't keep a fuse in it, it blows. I guess I can do that without engaging the light switch.
Can you elaborate on that test. There's only 6 sockets. 2 parking lights in front, and 4 bulbs in rear lights.

I've heard the dash lights might be part of the circuit, but it has a separate fuse. But they are connected to the switch.

I do have a suspect socket in the rear, but the blinker and brake lights work on that socket. Might be obvious to some how that can happen but not to me.

The bulbs have two filaments and the sockets two contacts fed by separate wires from the lights and turn signal circuits. The socket, with wires and bulb removed can be checked with an ohmmeter looking for a low/zero ohm resistance between between +12v contacts and socket ground.

After testing that one "suspect socket" socket, per bigchief's advice, check the circuit from the main connectors to isolate front verses back verses the switch.

Note that there is also one additional bulb fed off the rear +12v run, the license plate light.

If every thing in the harness checks out you could unplug the turn signal switch at the connector at the steering column and check if the turn signal switch is shorting. Remember that all of the lights run through the turn signal switch before they go out to the front and rear of the car.

Found it!
License Plate Light. Frayed wire touching the bumper. Lights are working and fuse is holding.
Now for a stupid question.
I took the two screws out holding that light in there, but how tge hell do I get it out? It's like a puzzle, the light is two big to drop down. Some big screws holding the bumper, or maybe a bracket needs to come out? Not sure but I know they did some bodywork back there, maybe the light used to just drop down. Not now.
Any thoughts?

I believe the bumper has to be removed.

Just came to that conclusion with a quick search. Bummer. Ill be screwing the light back in for now.

Thanks