Toyota Tundra Discussion Forum banner

Any way to make fog lights turn on ONLY with High Beams?

2K views 15 replies 4 participants last post by  Slate CrewMax 
#1 ·
Our trucks are set up stock to allow the fogs to come on only with the low beams. I am wondering if there is a way to only have the fogs come on with the high beams. I replaced my fogs with some driving lights and they aren't made to run with low beams.

I know there is a mod to use the fog switch with high or low beams, but I want to be able to only have the fogs come on with the highs so when I switch back to low beam the fogs turn off. Any ideas?
 
#9 ·
  • Like
Reactions: bamma
#11 · (Edited)
Internal Construction of Bosch relay:
The following diagram shows what those external terminals are connected to on the inside of the relay. When there is no difference of potential (voltage) across terminals 85 and 86 (the coil), the relay's movable contact (connected to terminal 30) is held, by spring tension, against the electrical contact which is connected to terminal 87a (the normally closed contact). In other words, when no voltage is applied the the relay coil, terminal 87a is connected to terminal 30. When 12 volts is applied to the relay coil (terminals 85 and 86), the movable contact (connected to terminal 30) is pulled down/in by the electromagnet (coil) so that it physically contacts the electrical contact which is connected to terminal 87. Again, in other words, if battery voltage is applied to the relay coil (terminals 85 and 86) terminal 30 will be connected to terminal 87. The red dashed line shows the path in which electrical current flows from/through terminal 30 to the contact of terminal 87a when the relay coil is NOT energized.
 
#16 ·
You could have the fogs to be able to turn on or off with the switch, but only when high beams are on. Sorta like BDT is saying. Just take the pink wire in the any time on mod to pin 85 like it shows. Then use the +12 from the actual high beam for pin 86. Then 87 would be to the battery and 30 would be to the positive side of the fog lights.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top