Kjduvall

Simple Fuse question, new 3500hd....... So I ordered a 2021 3500hd reg cab long bed, didn't come with fog lights so I bought everything except wiring harness. I will be making my own . So my question is what Fuse to run??? Single wire feed to a splitter/ then to power/ very short ground.. it's newer LED so I'm not sure... I was thinking 15 amp/ 7.5 per unit. If I go 20amp will it be (happy) or burn me down... Thank you in advance for all replys..

WhiteBird00

iTrader: (4)

You want to run the smallest fuse that won't blow all the time. Remember that the fuse protects the wire not the load device (in this case the fog lights). You want to be sure the fuse will blow in an over-current situation before the wire gets hot enough to be dangerous. Since you're making your own harness, one solution is to use larger gauge wire to ensure that it can handle any over-current possible with the size of fuse you select. There are plenty of calculators online which will tell you the right gauge wire and maximum length for use with a given current flow (plug in your fuse size as the amount of current).

That being said, I would think a 15A fuse would be more than enough for LED fog lights. That would give you about 11 feet of 16 gauge wire with only a 5% voltage drop (13.8 -> 13.2)... more than enough for fog lights. 11 feet should be plenty for wiring the power side of the fog lights at the front. You can use a relay and much smaller wire to go into the cab for the switch.

Kjduvall

Thank you whitebird00, I appreciate your advice. Prolly will go that route and with a relay. Once I get the truck I'll figure out a nice OE looking switch. I want full control ove it so I can keep fogs on with high beams. I see more deer on my way to work than cars.....

WhiteBird00

iTrader: (4)

An interesting option I installed on my wife's Grand Cherokee was radio controlled remote relays. They consist of a relay box that goes under the hood which is controlled by garage door opener radio frequencies (usually 433 MHz). Since we only have one garage door and the Jeep has three door opener switches (HomeLink), I was able to use one of those switches to trigger the relay without having to run any wiring between the engine compartment and the cabin. That gives you completely factory (and stealth) looking switch capability. The relays are around $13 each on Amazon - just look for 12V RF relay. If your truck has HomeLink or similar programmable built-in garage door opener switches then that might be an option for you.

With the relay and direct wiring harness, you will have complete control of the fog lights separate from any other system in your truck (including high beams). Just make sure you put the coil (switch) side of the relay on an ignition controlled power supply so that you don't risk accidentally leaving them on when you leave the vehicle.