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Make sure the fuse contacts are clean and the fuses are good.

Wiggle all the wire connections on the ignition switch and headlight switch to see if you have a loose one and or dirty one.

Make sure you battery terminals are tight. Loose terminals can do weird things.

Just a few ideas off the top of my head, you may have already tried them.

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Sometimes the dimmer swich can cause this. Hope this helps.

I would say the dimmer switch as well. Move it back and forth.

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Certified pilots, looking down on people since 1903.

On 78-80 LUVs there is a thermal circuit breaker up under the dash for the headlights instead of individual fuses for each bulb. It looks like a small rectangular relay, wires going into a metal covered doodad. It will reset itself after a minute or two if the power is off or the short removed. There is a lighting fuse, but if it blows it would take out all the other lights too. I'm guessing you either have a problem in the wiring somewhere (short that is tripping the breaker perhaps, or a disconnect somewhere) or the switch on the dash is having trouble. I wouldn't think the dimmer would make any difference though as it just controls the dash lights. It could be that both bulbs are toast, unlikely yeah, but if you are overcharging it could happen.

I would attack it something like this: Get a voltmeter and test for power at the bulb connectors, then check for power at the switch both before it and after. If power is getting out of the switch and not to the bulbs, you know it is in the wires to the bulbs somewhere. I can remember if the breaker is before or after the switch, I believe after, so check the wiring diagram on that one. It is sort of in/on the wiring bundle on top of the steering column. Basically, look for where you have power at one end and where you don't at the other, then test closer and closer together until you find where it disappears.


One theory that just came to me: It might be one of your bulbs blew in such a way as to cause a dead short in the bulb, and the breaker is tripping so the other side doesn't light up. Disconnect each one in turn and see what happens after letting it sit off for 5 minutes. (to reset the breaker)

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good

The dimmer switch I was referring to is the one that switches the headlights from high beam to low beam and vice versa. Not the one that controls the dashlights. The switching circuit in the headlight dimmer can corrode and not let the voltage through the contacts when switching. This was a common problem on early model cars with the floor mounted push type dimmer.

Oh yeah, my bad. That is another good item to check on.

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95 Isuzu Trooper Daily Driver
86 Isuzu Trooper reliable backup
77 LUV 2wd stock beltway blaster (resting)
79 4x4 LUV project: 2.6L, 5spd, 31s (eventually)

MEPR: Man, my 4x4 makes all other LUVs look good