GEN 2 Opinions/Input on wiring lights into the high beams.

[FordTechOne]

from the relay trigger connection? that much?

Yes, and most draw more than that.

 

[GordoJay]

from the relay trigger connection? that much?

At best. The activation current for automotive relays ranges from about 50mA to about 500mA. If you take pot luck and just grab any old relay that you have handy, you could be near either end of this range. I remember @FordTechOne posting the schematic of the BCM, but it wasn't in the thread you linked. IIRC, Ford is using high-side MOSFET drivers. Here's a short part-pimping intro to that scheme if you're in the mood to geek out. Reading it will help explain what's involved. https://www.digikey.com/en/articles/smart-high-side-drivers-help-meet-tough-new-automotive-standards

Edit to add link.

 

[smurfslayer]

Will check out that article. I think this helps clarify @FordTechOne’s advice to not tap the high beam circuit to trigger your lights. I can see it working under normal conditions, so long as everything else in the truck is perfect. I can also see it suddenly setting a DTC for some mysterious, unknown to us reason that could be related to a network fabric issue internal to the truck, an unusual electrical load condition, or maybe your truck isn’t charging as effectively, a low voltage condition, etc.

What about the low beam circuit though? Specifically, some of the F150s besides the Rap are wired for factory fogs. If I’m not mistaken, the wiring is still present on the Rap. Someone asked many moons ago if we could simply drop in an F150 headlight switch with fogs, and connect up some lights - saving 1 of the up fitter switches. I don’t know that anyone ever did it. But, that circuit should be an option - Fogs are permitted with low beams and turned off with high beams. it wouldn’t be the most elegant solution but

-could you safely use that as an option to relay in some after market lights? In other words, instead of the factory fog lights, have that setting trigger a relay or even just some rigid or B/D SAE lights?

 

[GordoJay]

What about the low beam circuit though? Specifically, some of the F150s besides the Rap are wired for factory fogs. If I’m not mistaken, the wiring is still present on the Rap. Someone asked many moons ago if we could simply drop in an F150 headlight switch with fogs, and connect up some lights - saving 1 of the up fitter switches. I don’t know that anyone ever did it. But, that circuit should be an option - Fogs are permitted with low beams and turned off with high beams. it wouldn’t be the most elegant solution but

-could you safely use that as an option to relay in some after market lights? In other words, instead of the factory fog lights, have that setting trigger a relay or even just some rigid or B/D SAE lights?

Interesting idea, especially if you can use Forscan to enable the fogs and the fogs are controlled by the BCM. You should be able to do this safely if you can figure out how much current the stock fog lights draw. Choose a relay that draws that much or choose fog lights that draw that much.

OK, I went searching and found the diagram that @FordTechOne posted earlier.

I don't see fog lights, but this may just be showing the connection between the BCM and the headlight assembly. We need to know if the fogs are driven the same way. @FordTechOne ?

 

[4x4TruckLEDs.com]

Fogs are on a different wiring circuit. Use a 2015 F150 with OEM LED headlights as an example. They have fog lights, but it's a completely different circuit/harness. It's not part of the OEM LED harness you have there. So that's why you won't find a "fog light circuit" on the Raptors.

NOW... knowing ford there IS a fog light circuit SOMEWHERE in there. I dunno if Ford separated the fuses or what not but I don't believe the Raptors use the same fuse panel layout as the regular 2015-2017 trucks. In fact im certain of it. 2015-2017 use mini fuses, 2018+ uses micro. But the 2015+ Raptors use micro fuses... unless it's just the 2018+ raptors that uses micro and the 2015-2017 raptors use mini... NOT 100% sure on that

 

[FordTechOne]

Interesting idea, especially if you can use Forscan to enable the fogs and the fogs are controlled by the BCM. You should be able to do this safely if you can figure out how much current the stock fog lights draw. Choose a relay that draws that much or choose fog lights that draw that much.

OK, I went searching and found the diagram that @FordTechOne posted earlier.

I don't see fog lights, but this may just be showing the connection between the BCM and the headlight assembly. We need to know if the fogs are driven the same way. @FordTechOne ?

The fog lights are also powered directly by the BCM using an FET. Here’s the diagrams.

View media item 15451View media item 15450

 

[GordoJay]

Thanks. It looks like the fogs are incandescent, not LED. That means that the BCM is likely less sensitive to a wider range of currents. It's more likely that the designers were mostly concerned about opens and shorts rather than the possibility of a misbehaving LED lamp. A good design will still try to match the nominal current drawn by the bulb used in the standard fog lights. And testing should still be done to verify at what currents, high and low, the BCM decides that there is a fault and that bricking the BCM isn't a problem if a fault persists. It shouldn't brick, because you wouldn't want a burned out bulb to cause that, but you never know.

 

[smurfslayer]

So.... if we keep it reasonable, that might be an alternative. complicated but more viable and at least potentially safer than high beam trigger.

 

[GordoJay]

So.... if we keep it reasonable, that might be an alternative. complicated but more viable and at least potentially safer than high beam trigger.

I think so. It's a lot more work, though. If I was young and hungry, I'd design, build, and sell a little PC board with a transistor-driven relay on it. Then you could just do the high beam trigger and not look back. It would be dirt cheap to build, you could sell them for quite a lot more, and there are a lot of vehicles that use or will use high-side driven LED lights, so there's a big market. Someone could jump on this and make some good money.

 

[KeithV]

I've been considering this too and I've heard the warnings, but also people saying they've done it and haven't had problems. I'm a total idiot compared to a lot of you guys on here about the newer electronics and BCMs. The one thing that confuses me a little bit is the quote FordTechOne put from BBAS:

“Never drive additional electrical load directly from the Body Control Module (BCM) output. The BCM output must drive an auxiliary relay coil only. If you try to drive an aftermarket electrical load directly, the BCM will likely disable the output and you may have to replace the BCM.”

To me, that appears to be saying you shouldn't drive lights directly from the BCM, but you should use a relay coil. If they didn't say the relay coil part, and just said don't drive additional electrical load from the BCM, then I can understand not attaching anything into that circuit. But when it states about driving an auxiliary relay coil only, it seems like that is acceptable. I'm confused LOL

Also, it was stated that first it would throw a DTC, and then shut down the circuit if it continued. So does that mean your lights would stop working and you would know there was a problem before it completely bricked the BCM?

Sorry for my ignorance. The much tighter electrical tolerances on these newer vehicles certainly aren't something to be screwed around with. I will always take the safe road, I'm just confused by some of the wording and descriptions.