TheGrimJeeper

I'm working on one of these as well. This was the schematic I came up with. I chose to go with a blue sea fuse block. Anyone have any comments or suggestions?

countrydude1992

Looks good! Just be sure your fuse for the main block is closer to the battery. I'm guessing it's just there for the diagram.

And the more I've thought about it, I actually really like 14Sport's idea about switching the negative side of the relay instead of the positive. One less wire going into the cab and less potential for mishaps from active wires running through the firewall.

TheGrimJeeper

Thanks! Yeah it will be closer to the battery and it is actually a 100A circuit breaker. I'm still not quite sure I understand the concept of switching the negative side of the relays though.

countrydude1992

Ok so in your diagram you have a hot wire coming from the top right 3amp fuse in to the cab to provide power for the switches. this power in turn activates the individual relay depending on what switch you flip right?

And then on the relay side, you have all of the grounds jumped together.

Now to activate a relay, it needs a hot input, and it MUST be grounded. Most people would use a switch to kill the hot input, like you show in your diagram.

But you can also use a switch to kill the ground, thus killing the completed circuit, which deactivates the relay. (Easy way to think of this is if you have something connected to a battery, you can take off the positive OR negative connection and it still turns off right?

The reasoning for this is less wires going into the cab, and should one of the wires become damaged, its much easier to deal with a faulty ground wire than a faulty hot wire. When ground wires get shorted, a light may not turn on. When hot wires get shorted, things can spark and catch on fire.

Hopefully that made sense?

14Sport

Been doing it this way for years.

And you can eliminate 2 wires going into the tub by using one of the many grounding lugs available. We are talking milliamperes here, not nearly enough draw to warrant returning to the battery. At least that has been my experience. Be forewarned though, once you do it that way you'll never go back to switching the positive.

I really have to credit GM for teaching me this. Back in the day I bought a Trans Am with a built 400, which are notorious for running hot. I wanted a way to manually turn the cooling fan on without putting a huge switch inside the cab. Most of my previous wiring experience was installing stereos. So I looked at how the fan was wired and drew a schematic of it. I didn't know anything about relays so had to research how they worked. This made me realize that GM was using the temp sensor in the head, which is nothing more really than a switch controlled by temperature, to ground the control circuit to the block to turn the fan on. The positive side of the control circuit was wired directly to a 12V source. I figured out that I could just run an alternate grounding path to get the same effect. I simply tapped into the temp sensor wire and ran it to a mini toggle on the dash, with the other side going to the nearest ground. I could control the fan myself but it also allowed the temp sensor to turn the fan on if I wasn't paying attention. Been doing it that way ever since.

TheGrimJeeper

Ok, that makes a lot of sense actually! So I would remove all the hot wires coming from the switches to the relays and just wire the relay's switch power from the other 6 terminals on my fuse block? Well I guess they could actually be daisy chained since they are going to be such low draw right? Then if I understand correctly, I'd take the grounds from the relays that I daisy chained and wire them to the appropriate switch to effectively switch the grounds? Sorry for beating this to death, I just want to make sure I've got this right before I wire it all up and hook this thing to the battery. I'm much more mechanically inclined than electrically so but I'm trying to learn some things haha

countrydude1992

Correct! Daisy chain your hot wires and individually switch your ground wires. This way on the switches you can have 3 of the 5 pins all daisy chained to a ground. Then one pin all daisy chained as hot from the dash lights (depending on your switch.) Then one pin each coming FROM your relays ground terminal.

14Sport

Yup. Just switch the grounds and unswitch the positive side of the control circuit.

Edit: The only thing I'm not sure about is if the top light will come on when you activate the switch since it's a ground circuit. Maybe countrydude knows or you can bench test it first as I always do. If I had one of those switches available I would test it for you as I have a 12v converter just for such purposes.

Edit again: I do have a bunch of relays around though and I believe a LED as well. Not sure if it's 5V or 12V though. If it's 5V I can throw a 330 ohm resister in between which I also believe I already have. I'm at work now so can't check. If you'd like, I could hook my converter to pin 85 on the relay and use pin 86 to feed the led. Then I could ground the other side of the led and see if it lights and sends the resistance across pins 30 and 87 to zero. I think this would be an adequate test (countrydude?) considering I don't have the physical switch.

I have a full schedule tomorrow as I'm installing a security system and I know my wife wants me to hang Xmas lights but I could definitely get to it on Sunday.

Let me know.

countrydude1992

It should definitely light it up when you flip the switch. The LED would still be part of the circuit. Even though it's the ground coming off the relay, it still acts as a hot coming into the switch. No matter where it is placed, it still has power flowing through it.

Now as for the "always on" light (the one that's on even if the switch is off) you will need a hot input for that. Most will tie into the dash lights so that LED comes on when the dash lights come on. But you could also wire it to come on with the key in the ignition.

14Sport

That's what I wasn't sure of. Thanks, countrydude.

As far as a dimmable source for the bottom array of LEDs, here ya go.

https://www.jk-forum.com/forums/jk-e...lights-311176/