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What's Happening With My Lights!

I have a 1998 Nissan Altima. It’s a good car, but a few weeks ago something weird started happening.
When I turn on the headlights. The high beam indicator on the dash lights up, even though it is not set on high. Note that the high beams are not actuated.
And, when I switch to high, the dash indicator stays on and the lights actually dim just a little bit.
So I have no high beam at all, and, my lights are a little dimmer than they should be.
I have replaced the switch and this did nothing.
Any ideas?

This kind of problem can get tricky to track down, but often ends up being a bad ground wire (or ground connection) somewhere in the circuit.

I wonder if the low beam filament in one of the headlight bulbs is making contact with the high beam filament. I’ve seen this happen in tail light bulbs where the brake light filament cross connects with the tail light filament. I suppose this could happen with a headlight bulb. You might want to change the headlight bulbs.

I agree with @Uncle Turbo. Try cleaning the ground connections going to the headlights and under the hood and see if that makes a change. If that doesn’t help then there may be an internal problem with the module for the lights.

An auto-electric mechanic could check the headlight filaments resistance with a DVM, wouldn’t take much time. And he’d check the voltages too. That would probably provide the clues needed to find the problem.