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Originally Posted by The Grand Pooh-Bah
I want the ability to turn my 2001 factory fog lights on without the headlights or parking lights, yet keep the factory switch functional. I'm thinking along the line of adding a switch with a relay that will power the lights on demand. Will this cause any issues by sending power back thru the factory harness/switch?
If I’m following you, the fog light switch would be turned off, through the headlight switch pull knob—so nowhere for it to back feed if your tying into the 12 v supply at the fog lights that runs along the front bumper. By all means fuse but I’m not sure why you’re using a relay unless you’re wanting to use a very small wire to trigger the relay and pick up 12v power nearer the front of the truck. Not unusual for more than one 12v Supply tied into same circuit (example: 12v bilge pump on a watercraft)- one for float switch and another for manual on/off. I recently had my fog lights out from the front of my truck (2002) but don’t remember what gage the wires were—IMO, if I was going to do it that’s where I’d tap in with a fused wire of the appropriate size/and a switch. Get some other opinions from the guys on here but see no reason why it wouldnt work. My Boat doesn’t have a computer to worry about 😉
Note: on classic cars the use of a relay is often used when upgrading to halogen headlights as the oem wiring will not handle the amp load of halogens safely- but will trigger relay off/on and then picking up a heavier gage 12v wire, supplied from a fused distribution block/battery to the relay on the power in/ and on the out providing power , which is what I’ve done on my 59
2002 F350 7.3L / 4R100 - 4WD CC DRW 8’ Box, AIH Delete, Gauges- Pyro, Trans Temp, Boost, Fuel Pressure, TS-6 tuner, Zoodad Mod, Mishimoto 31 row Trans cooler, Mobil 1 ATF, Trans return line ATF filter, Hutch/Harpoon Mod, Air Lift Load Lifter 5000 rear air springs, Rancho 9000 shocks, Timbrens on the front.