Fog lights burning out low beams

We have a 2010 Toyota Tacoma Off Road...we turned on our fog lights and it seemed to blow our low beam lights. We replaced the head light dimmer switch and light bulbs, all fuses were okay. In testing everything worked great until I turned on the fog lights ... again blown low beam lights, seems to be the fog lights creating the issue. Anyone else with this problem? Any suggestions?

 

Assuming both are on a similar fuse (and that’s a big assumption on my part) I’d start by getting a multimeter and check from the back of the fog light and check continuity with ground/frame. Sounds like you have a short somewhere.

 

Kinda head-scratching, as OP is saying the bulbs are blowing, but the fuse(s) aren't... a halogen bulb is basically a controlled short circuit, about the simplest load there could be, it's got 'x' resistance, apply 12v across terminals, it draws 'y' amps.

The only thing making sense in my head is that the fog light bulbs are somehow now in series with the low beam filament, lowering the voltage and therefore increasing the amperage, but aside from someone improperly wiring in non-plug-and-play fog lights, I don't see how that could happen.

OP... are the low beam bulbs actually blown (open circuit with a meter, or a visible break in the filament) or do they just stop working? And did you replace the switch because this happened, or did this start happening after you replaced the switch? Cuz a problem with the switch makes a lot more sense than the explanation above...

 

Yep, I read that wrong.

 

Did you do the fog light mod? It definitely sounds like a short when you put the switch on.i would isolate each headlight bulb and turn on the switch. You may have a short in the headlights. Did you replace them recently?

 

Remove & Replace your FOG relay.