I hooked up some Hella 550ff lights this weekend. I originally had them installed on an Isuzu Rodeo years ago. I hooked them up following the wiring diagram. I tapped into the low beam power wire since in Pennsylvania fog lights must only operate with the low beams. However, they come on with the low beams, which they should, but do not go off when the high beams come on. I used the original wiring harness/relay that came with the lights. The only thing that is different is the switch I used. There are 3 wires leading to the switch (power/load/ground). The switch I used does not have a ground terminal, so the ground wire does not hook to anything. I figured the ground was just to operate the light on the switch so that shouldn't be the problem. Could the relay be bad. It must be working if the lights come on only if the low beams are on. Any ideas would be helpful.

Thanks

 

What year is your truck? Could it be that the power is fed to the hi-beam and lo-beam via the same wire if it's pre 98?

 

It's a 1999. I should check whether the low beam power still has power when the high beams are on.

 

I got the lights to turn off when the high beams come on by hooking the ground wire from the relay to the low beam ground instead of the chassis.