Wiring/Amps Tech Question

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New recaros

FRF Addict
May 23, 2019
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The answer is:

It depends.

You’re close and you have 2 variables here.
The truck voltage at KOEO / while the truck is running
the voltage B/D calculates the current draw at.
( I know, this is a very simplistic example )

because when voltage drops, current draw can go up.

so using an ohm’s law calculator - extreme examples, if I have 12v 8.5a I have 102w of power. at 14.4v, 8.5a we have 122.4
I’m not even bringing up resistance and voltage drop here.

before it gets out of hand - and I already need to top off my pint, you’re close enough that a relay is inexpensive insurance for the up fitter circuit.

Wire in a relay. I don’t know if I’d go as far as a relay for every up fitter, but if it’s close, it’s worth it to have the added precaution.
I don’t think your calculation represents what happening.
If your light is rated at 8.5 amps at 12 volts, then it has a consumption of 102 watts. As you stated. But, If you raise the volts to 14.4, your amp draw will drop to 7.08 amps.
Amps x volts = watts.

Baja Designs

Supporting Vendor
Supporting Vendor
Apr 12, 2012
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I would like to run 2 BD S8 10” lights off the Gen 3 Aux 1 switch (previously the inner fog.)

Aux 1 is 10 amp rated
BD rates each S8 10” at 4.2 amp
*I will not be using the backlight feature*

Obviously 4.2 x 2 = 8.4 amps, which is below the 10 amp rating for Aux 1, but it’s close.

Good idea or bad idea?

@Nex @smurfslayer @The Car Stereo Company @Baja Designs

I have had many people wire up two S8 on to a 10amp circuit without any issues. The only way you might encounter issues is if a light is faulty and is reading higher amps then it should be. Other than that, you should not encounter issues wiring them dirreclty to you up-fitters.

The harness you would need if wiring to up-fitters would be:

OnX6/S8/XL Upfitter Wiring Harness - Universal


OnX6/S8/XL 55 Inch Splitter - Universal

If you want a harness with a relay then this would be:
OnX6 (10"-20") / S8 (10"-30") On/Off Wiring Harness - Universal
OnX6/S8/XL 55 Inch Splitter - Universal


May 2, 2023
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North Port FL
Theres some weird electrical math going on here and I don't have the time to correct it all. The bottom line is if the 2 lights combined are below your rated fuse amperage then I would go ahead and run it like that. There are already relays wired in to the auxiliary switches so there is absolutely no need to add more relays. The amperage protection is to protect wiring, terminals and the junction box that provides the power to the customer access points.

IF the lights do overload the circuit, the fuse will blow and you will know that you need to figure something else out.

Also, your truck should have 2 upfitter switches that provide 15 amp fused power, unless you already used them.



Be vewwy, vewwy quiet. We’re hunting sasquatch77
Dec 16, 2016
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as stated, use relays. im even more cautious as to use relays at 75% the amperage rating. also, the guage of wire is just as important. minimum of 16ga wire and 12 to 14 for longer runs. you lose power through heat and too small of wire will generate too much heat. feel free to text me and i can give you a complete layout and explain how it works and answer any questions you have (831) 254-7562

I’m sayin.
except most newer vehicles dont go above 14 now....... jeez watt were thinking?
let’s not get all amped up here.

Most of my screw ups were pre-Raptor, but, I’ve had 2 opportunities to learn.

1: I tried adding in reverse lights; B/D squadron sports without a relay. I tapped a circuit that -should- have been good enough; at least I thought it should have been good. Unfortunately for me, the engineers at Ford thought otherwise. I got them hooked up, cycled them on / off and it worked. Then I thought “WTH I’m already here, let me grab a relay, and wire to up fitter and reverse. Oh heck, I don’t need to run all the way to the battery for constant 12v+, let me just grab it from this handy +12 volt bed light circuit." That worked too, several times. About the 7th or 8th time, leaving it on for a few minutes, they went dark along with some of my cab lights, bed lights, etc. I searched high and low for a busted fuse, to no avail. FORSCAN to the rescue. I tripped a DTC overloading the circuit. Cleared and wired to the battery like I should have in the first place. DOH!

2: while re-allocating my up fitter switches, I inadvertently connected my pair of LP4’s to my squadron circuit. popped the fuse in the harness - again, these came on and ran and stayed on... then, just went dark... I hate that feeling of “did I really just blow a fuse here? seriously? “ Yes, I did.