Easy Roof Light Bar Wiring DIY

[Demon4x4]

This is exaclty how I did mine.

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[cr117]

Switch 1 is rated at 30 amps and engineers aren't dumb the wiring got changed for that 30 amp fuse, and wiring can flow surprisingly high current through a surprisingly small wire.

Length of the wire matters. For a 16 AWG wire to travel 8+ feet to get to the roof, carrying close to 30 amps, it's a gray area at best. Personally, it's not something I'd want to risk and be responsible for.

 

[denneyt]

Length of the wire matters. For a 16 AWG wire to travel 8+ feet to get to the roof, carrying close to 30 amps, it's a gray area at best. Personally, it's not something I'd want to risk and be responsible for.

or you know the ford engineers thought of this. let's use the kc 50" bar as an example, each light on the bar has a 1.78 amp draw times 8 lights and you get a 14.24 amp draw for the bar. now the upfitter switches are not wired in series with the circuit they are just the control circuit for activating the accessory circuit. so based on fords ratings switch 2 is the appropriate switch for this light bar using the chart you posted 16 gauge is plenty for this light bar as that rating is for a straight wire with nothing in the circuit which is not true for the bronco accessory which is joined at multiple places (a crimp does not extend the length of the wire).
the chart you posted show this light bar would need around an 18 gauge wire to properly power it and the 16 gauge would be just fine.

 

[cr117]

or you know the ford engineers thought of this. let's use the kc 50" bar as an example, each light on the bar has a 1.78 amp draw times 8 lights and you get a 14.24 amp draw for the bar. now the upfitter switches are not wired in series with the circuit they are just the control circuit for activating the accessory circuit. so based on fords ratings switch 2 is the appropriate switch for this light bar using the chart you posted 16 gauge is plenty for this light bar as that rating is for a straight wire with nothing in the circuit which is not true for the bronco accessory which is joined at multiple places (a crimp does not extend the length of the wire).
the chart you posted show this light bar would need around an 18 gauge wire to properly power it and the 16 gauge would be just fine.

Except OP installed a Heretic 40" light bar, which according to their specs, pulls 25.4 amps.

 

[kd.overland]

I am literally installing my 42" lightbar from Diode Dynamics today in a similar fashion. I chose to go through the firewall into the glove box, then through the inside door trim.

I had to trim off about 10.5/16 of an inch off the Trailrax Fairing to make it a snug fit.

 

[Charlotte Kev]

I am literally installing my 42" lightbar from Diode Dynamics today in a similar fashion. I chose to go through the firewall into the glove box, then through the inside door trim.

I had to trim off about 10.5/16 of an inch off the Trailrax Fairing to make it a snug fit.

Nice! I just didn’t want to mess going thru firewall and glovebox etc. Multiple was to install. Should look really good.

 

[denneyt]

Except OP installed a Heretic 40" light bar, which according to their specs, pulls 25.4 amps.

so switch 1 would have worked for them as the circuit is rated for 30amps. I just don't get thinking that the engineers (bane of my existence as a tech) don't adjust the wiring to handle the amperage they are rating it for, the legal issues for ford would be astronomical if they rated it and it couldn't handle the rating. now if op has wired a winch in switch 1 then totally agree for his light bar he needs a aftermarket harness.

 

[GlueBoy]

I'll look for the link later but I was looking for better methods of routing roof lights to the AUX trace behind the passanger sun visor and saw that Ford routed their Rigid light bar under the front of the weatherstripping at the corner of the hardtop up front.

So far it's done a great job. I do get excess wind noise from that corner when it's cold though. Like sub 40.

 

[cr117]

so switch 1 would have worked for them as the circuit is rated for 30amps. I just don't get thinking that the engineers (bane of my existence as a tech) don't adjust the wiring to handle the amperage they are rating it for, the legal issues for ford would be astronomical if they rated it and it couldn't handle the rating. now if op has wired a winch in switch 1 then totally agree for his light bar he needs a aftermarket harness.

That's the thing though, the Ford engineers didn't design a complete wiring system for aftermarket accessories. We get some wires not hooked to anything that lets us, as the consumer, decide what we want to do with them. The switch wires are rated correctly, but if you try to run 30 amps all the way up the roof with what Ford provided, it's not sufficient. I can't explain why Ford chose to do this, maybe it was all for marketing, but they clearly didn't plan for all scenarios.

If you're fine with running that kind of current through the tiny wires they gave us, fantastic. Ford's not responsible for electrical fires that results from modifications we make to our vehicles.

 

[Charlotte Kev]

so switch 1 would have worked for them as the circuit is rated for 30amps. I just don't get thinking that the engineers (bane of my existence as a tech) don't adjust the wiring to handle the amperage they are rating it for, the legal issues for ford would be astronomical if they rated it and it couldn't handle the rating. now if op has wired a winch in switch 1 then totally agree for his light bar he needs a aftermarket harness.

If you do that good for you. Why does it bother you so much that I went with a harness? I would rather go with harness and not risk it. Recommend by Heretic as well.

 

[denneyt]

That's the thing though, the Ford engineers didn't design a complete wiring system for aftermarket accessories. We get some wires not hooked to anything that lets us, as the consumer, decide what we want to do with them. The switch wires are rated correctly, but if you try to run 30 amps all the way up the roof with what Ford provided, it's not sufficient. I can't explain why Ford chose to do this, maybe it was all for marketing, but they clearly didn't plan for all scenarios.

If you're fine with running that kind of current through the tiny wires they gave us, fantastic. Ford's not responsible for electrical fires that results from modifications we make to our vehicles.

Just using the chart that's been posted here, and 11 years doing electrical diag at a dealership I can say it's plenty sufficient as a customer (not a consumer) the rating people see in that chart is for a continuous unbroken wire. Crimping 2 wires together doesn't make it a single wire it's still the length it was before it's what 3feet from fire wall to top of the roof? Which is well within the 30 amp rating for circuit 1 on 16 gage wire, same goes for the wire across the fire wall being 4-6 feet being well within the rating for 16 gage at 30 amps. The ratings in these charts are pretty misleading if you don't understand what they're saying which isn't that the entire circuit being 16gage can only handle so much, it's saying that each individual wire can handle that specific amperage at the set length of the individual wire.

 

[denneyt]

If you do that good for you. Why does it bother you so much that I went with a harness? I would rather go with harness and not risk it. Recommend by Heretic as well.

No run a harness if you want, but the wiring in the truck can absolutely handle the amperage is what I'm saying. Not specifically about you running the harness more about people thinking bigger wire means better, when that's really not the case.

 

[cr117]

Just using the chart that's been posted here, and 11 years doing electrical diag at a dealership I can say it's plenty sufficient as a customer (not a consumer) the rating people see in that chart is for a continuous unbroken wire. Crimping 2 wires together doesn't make it a single wire it's still the length it was before it's what 3feet from fire wall to top of the roof? Which is well within the 30 amp rating for circuit 1 on 16 gage wire, same goes for the wire across the fire wall being 4-6 feet being well within the rating for 16 gage at 30 amps. The ratings in these charts are pretty misleading if you don't understand what they're saying which isn't that the entire circuit being 16gage can only handle so much, it's saying that each individual wire can handle that specific amperage at the set length of the individual wire.

What are you talking about? Are you saying I can connect a bunch of 3ft 16 AWG wires together and not have any issues?

No, if you connect two 3ft 16 AWG wires together, that’s the same (or more likely worse) than a single 6ft 16 AWG wire. You don’t get to magically maintain the ampacity of a wire by simply cutting it in half and then crimping it back together.

The length of the wire affects the resistance on the current. The longer the wire, the more resistance that current will face. That resistance is emitted as heat. If you’re trying to transmit a current over a given distance, you don’t want too much resistance or the wires will melt. That’s the point of the referencing chart like the one I posted earlier. I don’t understand how a technician doing electrical diagnostics doesn’t understand these basic laws of physics.

 

[Tex]

I want to give them A for effort here…but can’t. Really weird how they thought all of this out just to put a tiny wire gauge.

Maybe, and hear me out because it's a stretch....maybe the point of such a small wire wasn't to use it to run current, but rather to use it as a fishing tool to run appropriately sized wire through the same route. Just butt splice the proper gauge wire to it and pull it through, then cut the new wire to length and crimp your terminals on the ends. I had that idea in the planning stage but then realized this route would be quicker once I actually dug into it. It's really not any cleaner of an installation than the way we did it.

 

[cr117]

Maybe, and hear me out because it's a stretch....maybe the point of such a small wire wasn't to use it to run current, but rather to use it as a fishing tool to run appropriately sized wire through the same route. Just butt splice the proper gauge wire to it and pull it through, then cut the new wire to length and crimp your terminals on the ends. I had that idea in the planning stage but then realized this route would be quicker once I actually dug into it. It's really not any cleaner of an installation than the way we did it.

I'm pretty sure all the pre-run wires are wrapped up in wiring harness. I don't think you can just pull through a single wire.

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