Relay and switch advice
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New User
Joined: Jul 2013
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Relay and switch advice
Hi everyone, I'm getting ready to add some offroad driving lights to the roll bar on my 75 f100. I've added relays into the headlight circuit to improve the brightness but in that case the switch power was already piped to the switch via the factory setup. Since I'm going to be adding two new switches into my truck where should I pull the power for the switches? Should I go all the way back to the battery or is there a better closer option?
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
I do not recommend switching power to the off-road lights directly. You should do this with a relay. Run hot-at-all-times power for the lights through the contact side of the relay. Trigger the relay coil with a light-duty switch, which can use keyed power if you don't intend to run the lights with the truck OFF. Your off-road lights would then be gated by the relay, which itself would be gated by the in-cab switch. The relay rating depends on the wattage of the lights. You have quite a bit of freedom in selection of the switch, since the coil of a common automotive relay is a fairly light load.
Watch the voltmeter at idle after everything's up and running to make sure your alternator can handle the load.
Junior User
Joined: Jul 2012
Posts: 96
Likes: 0
From: Monticello, Arkansas
Much like fmc400 I would pull the power off of the battery and fuse it. In fact, that is exactly what I did for my roll bar lights. I have four lights, two switches. One for the inside two and one for the outside two. A little overkill, but I didn't want the wattage of all of the lights on one circuit. Good luck!
Here's my truck for some inspiration. These trucks look awesome with a roll bar and lights in my opinion.
Here's my truck for some inspiration. These trucks look awesome with a roll bar and lights in my opinion.
Junior User
Joined: Jul 2012
Posts: 96
Likes: 0
From: Monticello, Arkansas
HIO Silver, I need to fab something up like that. With my lights on at night the whole inside of the cab is also lighted up. It'd be nice to have them forward of the back glass like yours.
Fleet Mechanic
Joined: Feb 2011
Posts: 1,410
Likes: 42
From: Michigan
Looks like a standard clamp-on drip rail roof rack alot of guys put on vans to carry ladders and such. Pretty common item.
Fleet Owner
Joined: Dec 2009
Posts: 20,678
Likes: 82
From: NorCal
It's not so standard.. it's cut down and the clamping system is reconfigured. The hardware also has to be removed in a certain order such that it is not easily removable by a thief.
If you're lighting up the cab, consider fabbing/installing a shield to bridge the gap btwn the lenses and the back of the cab roof. OR - fab a hoop welded to the "roll bar" to move the entire assembly forward. Generally, it'd be called a safari rack like this one:
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