What might be the problem if a 1997 Isuzu Trooper's low beams are out but the high beams still work?

Answer 1

Answer

Hi, there. This is exactly what happened to my '99 Trooper. Believe it or not, both the low beam filaments went out at the same time. I replaced on bulb and, bingo, low beams worked. Then, I replaced the other bulb and got the same result. Good luck. Hope this works for you.

-------- Hello, this is Lee adding a bit more to the answer.

Burned out bulbs suggest "high vehicle voltage levels".. High voltage levels are caused by a battery developing high internal resistance or a high resistance in the battery ground cable.

Automobiles typically use an alternator that charges the battery at a constant current. If the battery or the wire connecting the battery's negative terminal to the engine block develops a high resistance, then the voltage of the entire vehicle climbs a half a volt or maybe even a whole volt above normal. It turns out high intensity headlight bulbs quickly start blowing out when they are fed a little too much voltage.

So here is a checklist.

1. Check the voltage drop for the battery to engine block ground connection. Check the battery connections. Remake as indicated.
   
2. Does the battery need water? Not a very common problem these days, but small battery vehicles like motorcycles will develop a cell with low water.
   
3. Is the vehicle battery at it's age limit? Aging car batteries sometimes develop higher internal resistance.