Best place to get power for driving lights?

Sounds like a good plan, thanks again!

Note that I edited my post with another diagram.

really good relays (actual bosch, a few reputable Bosch clones like hella etc) will have a fly back circuit built in so the collapsing magnetic field in the coil gets shunted to ground instead of going back up and arcing the switch contacts.

if you think you might in the future add more relays in that area (cab, fender, etc) lay them in now amd use a heavier guage wire ( 10for example, or twin 12s or triple 14s) to feed them power now, and do the grounds now, so you aren’t having to go back and run even more wiring later, or add more grounds.

and please do not rely on the stupid yellow/blue/red plastic insulators on your spades or rings. Pull those off amd use red heat shrink top to bottom of the female fitting for 12v power black for ground, amd white or green for signal. One day, when you are trying to remember what fgoes where after taking it off or replacing it, you’ll be happy. And less chance of cross wiring or of accidentally shorting across one.

Erik the Awful said:

Relays are not polarity sensitive, so it's up to you how to run power and ground. The standard is to use terminals 30 and 85 for (+) and 86, 87, and 87a as (-) even though the diagram below shows 86 as power and 85 as ground.

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Can someone please explain as I genuinely do not understand how the coil can be insensitive to polarity and still move in the required direction wired either way? (I was trying a four pin relay as a fuel pump relay that could be inserted in the board in two possible orientations - which would be opposing polarities for the coil - and couldn't figure it out).

Onizukachan said:

really good relays (actual bosch, a few reputable Bosch clones like hella etc) will have a fly back circuit built in so the collapsing magnetic field in the coil gets shunted to ground instead of going back up and arcing the switch contacts.

Click to expand...

Preventing arcing across the switch - and protecting ECUs that are switching. But, does the presence of such a diode not make the relay coil polarity sensitive?

Grab the power from the battery and run the toggle inside the cab. Ran this setup on my crawler and never had any problems.

Pinger said:

Can someone please explain as I genuinely do not understand how the coil can be insensitive to polarity and still move in the required direction wired either way? (I was trying a four pin relay as a fuel pump relay that could be inserted in the board in two possible orientations - which would be opposing polarities for the coil - and couldn't figure it out).


Preventing arcing across the switch - and protecting ECUs that are switching. But, does the presence of such a diode not make the relay coil polarity sensitive?

Click to expand...

the Moving part of the relay is ferrous but no5 magnetized so either N or S would attract it and close the circuit.

the ones with fly back are shall we say Prefered polarity as far as where ground goes, from my experience wiring it wrong just defeats the fly back.

hope that helps!


and that’s without getting into ground switched vs positive switched or putting your switch on the positive or negative side of the relay. for what we are doing and the amperage’s we are talking about it doesn’t make much difference.

Hey HotWheels,

Have you moved forward with the installation of these lights?

No, still sorting out the relay, wiring,etc. Not being currently employed except for swap meets isn't helping! I have another show on Saturday that hopefully will add to the funds(rent is due on Thursday so that's going to take a hit on the wallet!).
What I want to do is get a relay with a bracket on it, so I can mount it under the hood. Was going to use a fuel pump relay as it has the right pinouts, but no bracket on it and no pigtail available either....
What really sucks about this project, is my cousin that we lived with for a while, is an electrical genius and could whip up a harness, switch, relay , etc. in very little time, but we are are no longer in contact because of why we don't live with him anymore. I could collaborate with him on a couple of electronic lighting ideas I have for my trucks, and we could make them, if his wife didn't have so much control over him.....

To answer the original question, grab power from the back/firewall side of the fuse box. You will need a maxi fuse (40/50 amp or so if not already there) to energize those big bolt terminals, but that’s what I’m using, and they are ignition switched so you can’t accidentally leave lights on.

feed power down along the fender well to where you put your relay, then from down the rad/core support to the under bumper area amd front of truck.

I have mine set up on a factory fog switch, but I generally just leave it switched on so they are always on when ignition is on.

HotWheelsBurban said:

No, still sorting out the relay, wiring,etc. Not being currently employed except for swap meets isn't helping! I have another show on Saturday that hopefully will add to the funds(rent is due on Thursday so that's going to take a hit on the wallet!).
What I want to do is get a relay with a bracket on it, so I can mount it under the hood. Was going to use a fuel pump relay as it has the right pinouts, but no bracket on it and no pigtail available either....
What really sucks about this project, is my cousin that we lived with for a while, is an electrical genius and could whip up a harness, switch, relay , etc. in very little time, but we are are no longer in contact because of why we don't live with him anymore. I could collaborate with him on a couple of electronic lighting ideas I have for my trucks, and we could make them, if his wife didn't have so much control over him.....

Click to expand...

I can identify with everything you wrote, especially regarding the bad habits, such as rent, electricity, etc.

I knew that I had a harness kickin' around that I wanted to send you, and I found it this morning. Unfortunately, it's a plug and play H4 harness from one of my bikes that really wouldn't be worth chopping up for an auxiliary lamp setup.


I misremembered, sorry M'lady...I am still looking for bracketed Bosch or Hella relay that's playing hide-and-go-seek. I think it's hiding with what's left of my brain.