Headlights won't work on my 1996 GMC sierra

My best guess is a bad ground common to both headlights.

I think the 50 amp fuse is for your starting circuit, not the headlamps, which is a 15 or 20 amp fuse. Did you try both dim and bright settings?

Since you don't know which fuse is for what, just remove and replace each fuse one at a time. As you go, visually inspect each fuse and test for continuity with an ohmmeter, then use a pink pearl eraser to clean the wafer tips before replacing. Do this methodically one at a time and replace any bad fuses with THE EXACT SAME AMPERAGE RATING.
Now, if your fuses are clearly marked and you do have a 50amp fuse in your headlamp circuit then you need to put the correct amperage in ASAP. If you have a 50 amp in the headlight circuit the whole circuit could be fried before the fuse blows, which is why you NEVER replace a fuse with a higher rated amperage.

Once you've worked over the fuseblocks go to the headlamp circuit and follow the wires and plugs coming from the lamps and going to the fuse block. Look for ground connections and tighten those, especially those coming from the headlamp wiring harnesses. If your lamps are good, the fuses are good, the plug connections are clean and making good contact and your grounds are good then all thats left is your headlamp switch and wiring to and fro. If you don't know what the plugs are for no harm can come from cleaning and reconnecting them, so you can't go wrong if you just do one at a time in a methodical fashion.
I have an old S-10 and the headlamp switch is junk- I have to hit it with contact cleaner every once in a while because Houston air quality is poor and there is a lot of ozone- all this corrodes connections- fuse maintenance cures a lot of ills.
After the fuseblocks I'd start by checking the actual headlamps to make sure they are working (check each filament for continuity or put 12v to it to test) and clean the contacts.

Then you can work your way back to the fuseblock and switch checking your plugs and connections. Its all pretty straightforward, just be methodical and clean your plug connections as you go. No schematic needed- just a little patience.

One thing to think about if your headlamps are both blown is that your alternator may be overcharging, or the regulator isn't working properly and your headlamps are blown because they got hit with too high a voltage. Eventually this will sulfate the battery and cause an internal short- if it is bulging you can be sure this is happening. So get your alternator and regulator circuit checked if this is the case.
Good luck, If this fixed ya then please rate this solution