Both Headlights Out

Check your grounds for corrosion. Also the fuse terminals associated with the power. It doesn't take much corrosion to cause intermittent chaos. Good luck!

 

Update - the headlight low beams are out all of the time now, that helps me trouble shoot. I started tracing back from the lights.

No power at the lights
Power on one side of the relay (it’s a 4 prong relay, the power is on the side opposite the battery
No power to either side of the fuses.

Time to find the schematic.

 

And I just found this, which explains a lot. Now I just need to figure out what it means and how to find the problem.

If you look at the wiring diagram for the 1st gen trucks, you will find something interesting. I am not sure WHICH year, if it was changed at all, but I know that the 95-99 Tacoma uses a ground circuit interrupt for the headlights and high beams. It works just the opposite of how you expect to see it done. When you turn on the headlights, the headlight relay applies power to one terminal of the head light. The other two terminals are high beam and low beam. Under normal operation, when the headlight switch is turned on, the switch supplies a ground to the low beam, thus illuminating the low beam. When you turn on the high beam, the switch sends a ground signal to the high beam ground, and removes the ground from the low beam. Now since the power is still applied to the low beam filament, the current still flows through the filament. This current then follows the high beam indicator circuit, applying power to the high beam indicator light. Since the high beam indicator light is a much lower resistance than the low beam, the indicator light will come on, but the low beam filament will still remain off.

This type of system was used years ago in the 70s Chevy pick up truck. If you remember those old-school trucks, the side marker lamp in the front was always on with the park lights, but when you turned on the turn signal, it would alternate the flash with the front turn signal bulb in the bumper.