75 c10 electrical question - head lamps / back up

[tard01]

hi guys, looking for verification/tip on troubleshooting 2 electrical problems i have.
1) head lights don't come on
2) back up lights dont come on


1) head lights don't come on - I can get the yellow lights to turn on via hazards or turn signals, so i know the wiring/bulb is good. I can also get the rear brake lights to turn on. But when fully engaged, the front lights (head lights and yellows) wont turn on.

Since i know the lever/switch to turn on the lights works (since rears turn on), i feel its ok.
since i know the yellows work via blinker/hazard, they seem ok.
I have not verified the actual bulbs themselves work on teh headlights.

Since the lever appears normal and hte individual lights come on for the yellows in other tests, i suspect a relay or fuse issue. Does this sound reasonable?

i visually inspected the fuses, i didnt see an obvious blow.

I found this fuse diagram, but didn't see which one specifically would be the one i need checked, but it did confirm that the turn signal and hazard circuits are seperate, which gives me hope the issue is a simple fuse problem.

http://www.chuckschevytruckpages.com/77fusebox.html

my best guess is that J is the head lights? though by the name, i'd suspect it was meant for the interior - not sure if panel refers to the front panel - doesn't seem to fit the name, but i dont see a better identifier for the front headlights.
J - Fuse - Panel Lights





2) back up lights dont come on - not sure if seperate issue, or maybe the bulbs are dead, but curious if anyone suspects it might share a circuit with the head lights, oddly? i'll verify its fuse location when i get sunlight tomorrow.




if at minimum someone can help me identify the name/slot of the headlights based on the labeling in the link i provided, that would help me quite a ***


side note - my continuity tester is scheduled to arrive today, but wanted to see if i couldnt identify the correct fuse prior.

[hatzie]

You'll find the 1977 GM wiring diagrams in my signature.
Check the light switch power.

Hazards, turn, & brake lights use the bright element of a dual filament bulb. Parking lights use the dim element. You proved the parking lamp ground is good.

Back up lights are on a different circuit.