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Hello,
I have a 59 GMC p/u and having a problem with my rear lights. I have no park/stop lights. Signals work and front lights all work. I checked the junction block under the cab and I have no power, has ground. Shows power when turn signals are on. Where does the power come from to that junction block? The fuse block under dash has power.
Thank you,
Bob

I did replace the turn signal last year. Of the two wiring diagram I have, they don't show the junction block under the cab. How does the junction block gets its power? If the the headlamp switch was bad, wouldn't the front parks lights not work? The front lights work fine.

there is no 'junction block' under the cab - there are 3 harness connectors about under the driver, and there is a stop light switch where the pedals go thru the floor, those are the wiring involved in the rear lights along with the main light switch .... here's the signal installation info, the connector setup is shown on pg 4 and there's a schematic of it at the end ... main switch wiring shown here ... sounds like you have possible wrong connections or broken wires, the signals should use the same wires as the brake lights to the back and the tail lights are a seperate wire direct from the main switch [via that group of connectors]

Bill

I jumped the two wires at the brake switch and the brake lights come on. When I turn on the park lights the brake light goes out and I still don't have rear park lights.

if you shorted the terminals of the brake light switch and the lights worked, but they don't when you push the pedal ..... bad brake light switch? check it with an ohmmeter

lite sw to park position and brake lites go out .... wires on switch wrong? what you think are brake lights are actually tail lights? [double filament bulbs, bright filament is brake]

"rear park lights" are called tail lights, they should be on with either the park light position or headlight position .... bad switch or wiring wrong?

you haven't said if the system ever worked, if it's all stock or an added on turn setup and hash wiring .... I'd guess you have some messed up wiring on a project, possibly a bad switch or 2, but it's time to get out the meter and wiring schematic and sort it out, the multiple plugs underneath might be wired wrong or damaged - could have a bad connection in the plugs or on a switch - could have a bad ground at the back - could easily be multiple problems

Bill

Bill,
They did work the other day. The wires are orignal and I checked all connections. When I looked up the headlamp switch it didn't look like the one that's in there. It's old and looks like it could be a replacement.
The brake lights work without the park lamps on, but when I turn the park lights on and step on the brake pedal they don't work. The rear park lamps are not working at all. The signal lights work and the front lamps all work fine.

that's not entirely clear .... the light switch should look like the assembly manual drawing I linked, is there a fuse on the lite switch?
the brake lights work properly as long as the light switch is OFF?
do the brake lights work with the switch in the main light position?
the tail lights don't work with the switch in either park or main?
do the blinkers work in back with the switch off? the blinkers use the brake light filaments ....

that would sound like it could be the switch if you lose power to the brake lights with the switch on, and have no tail lights - notice the wiring on the switch has the tail and park lamps separate [as above, park lights are front, tail lights are rear, there are no "rear" park lights] .... use an ohmeter to check the function of the switch

Bill

Bill,
The headlamp switch doesn't look like the assembly drawing and it doesn't have a fuse on it.
Brake lights only work with the headlamp switch off. Park or main lamp they don't work.
The signals always work no matter what.

sounds like it's time to get a proper switch and wire it correctly, the brake lights get power from a separate always-hot terminal on the switch, doesn't matter if the switch even works

Bill

Bill,
Thanks for your help. I ordered a new switch.

report the fix or further frustrations!

Bill