12V power for accessories

Oldstock14 · May 16, 2024

I’m looking to put in an under hood bus bar for pulling 12V power to my aftermarket gauges, probably some extra lights, usb power sources as well as fixing my no power situation on the factory “power source.” I want a clean organized source of power for more possible accessories in the future that’s also very easily accessible under the hood. I do use the truck as an overland rig of sorts, as well as the drive to work 1-2 nights a week.

Question is,

If I pull 12V power from the battery to the buss bar, then pull the 12v to my gauges, how would I put in a relay/what kind of relay would I need to prevent power when the truck is off? Obviously I could tie into key on power somewhere in the dash/fuse box but I’d prefer to start a whole new circuit to branch off to accessories so I don’t have to disturb the factory wiring. Can anyone throw out some ideas?

IDIBRONCO · May 16, 2024

One idea is that you could use the FSS wire in the under hood harness on the truck side of the big plug to power the on/off function of your relay. It has to be in there somewhere and it does work with the key.

Cubey · May 16, 2024

A continuous duty solenoid like this that activates when you turn the key.

Ignore the down for maintenance error it's showing here, the link works.

Advance Auto Parts - Down for Maintenance

Oldstock14 · May 16, 2024

IDIBRONCO said:
One idea is that you could use the FSS wire in the under hood harness on the truck side of the big plug to power the on/off function of your relay. It has to be in there somewhere and it does work with the key.

Now what about multiple relays? Could I use one relay for multiple circuits? Or would each circuit need it’s own relay so I’d need to branch off the FSS wire as many circuits I need

Oldstock14 · May 16, 2024

Cubey said:
A continuous duty solenoid like this that activates when you turn the key.

Ignore the down for maintenance error it's showing here, the link works.

Advance Auto Parts - Down for Maintenance

You power this solenoid from turn key power and then can use it for multiple circuits? Correct?

DaveBen · May 16, 2024

Yes you can use one power source to power multiple circuits. Just divide it right after the ignition switch. This is how automobiles have been wired.

Nero · May 16, 2024

If you use a constant use relay line cubey suggested, as long as its rated for the amperage of your desired use for key on devices, itlll be fine. Won't be hard to get, most are rated at 200 amps. I don't think you'll use that much.

WMO4IDI · May 16, 2024

Automotive relays are 40amps so unless you're powering something big with it, you can stack a lot onto it.

Personally I prefer to screw those inside the dash somewhere so it doesn't see humidity. I use the radio power wire to trigger the ones I use, that way it works on 2 key positions, accessories & run.

Cubey · May 16, 2024

Minuteman96 said:
You power this solenoid from turn key power and then can use it for multiple circuits? Correct?

Yes. That type of solenoid is typically used as a battery isolator, such as on old RVs, but your intended use works too. Put a fuse panel for the accessories fed off of the solenoid. And if you want to be extra safe, a fuse between the battery and the solenoid.

The easiest and safest wire to use for ignition switched +12v, that isn't vital if the fuse blows for some reason, is from the radio. Tap into that and run a single wire to the small post on the solenoid. That way, in the unlikely event the solenoid overloads on it's trigger circuit, you won't burn up your FSS wiring or something else that's required to work when driving down the road.

IDIBRONCO · May 16, 2024

Nero said:
Won't be hard to get, most are rated at 200 amps. I don't think you'll use that much.

The particular relay that Cubey linked says that it's rated for 85 amps in the description. I don't know what you're planning to power with a relay or your busbar, but just keep that in mind.

Cubey · May 16, 2024

IDIBRONCO said:
The particular relay that Cubey linked says that it's rated for 85 amps in the description. I don't know what you're planning to power with a relay or your busbar, but just keep that in mind.

Yeah, that's just the first example I saw.

Nero · May 16, 2024

Most constant duty cycle relays I come across at work are 50a, 100a, and 200a, I defaulted to the one that fails the most :smash:

Oldstock14 · May 17, 2024

DaveBen said:
Yes you can use one power source to power multiple circuits. Just divide it right after the ignition switch. This is how automobiles have been wired.

Yeah I knew that, but I didn’t know about overloading the FSS wire with multiple extra circuits attached to it. If I remember correctly, that wire isn’t very large. Thinking maybe tapping into the radio will be the better route

IDIBRONCO · May 17, 2024

Or you could use the FSS wire (or radio wire) to power one relay that, then, powers the other relays. That would complicate things, but it's a possibility.

Oldstock14 · May 17, 2024

IDIBRONCO said:
Or you could use the FSS wire (or radio wire) to power one relay that, then, powers the other relays. That would complicate things, but it's a possibility.

Okay so just to clarify from everyone’s ideas and info, I run a fuze box from my battery, to the accessories with the continuous relay inline between the battery and fuze box; that relay will be powered from the radio wire.

12V power for accessories

Oldstock14

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