GEN 2 Help with wiring relays for headlights

[dreys]

2020 Raptor

I have two sets of DD lights, that are wired up to Aux 1 & Aux 2 upfitter switches.

What I'd like to do is the following:

When Aux 1 is on, and headlights are on - have lights on
When Aux 1 is on, and headlights are off - have lights off
When Aux 1 is off, and headlights are on - have lights off

Same feature for Aux 2, the only difference I'd like to have those come-on when brights are on.

Does anyone which wire I'd need to tap into, and how would I wire that up with two 4-pin relays (one relay per set of lights)?

 

[dreys]

Ok, I think I found the correct thread:

https://www.fordraptorforum.com/thr...-connect-light-bar-to-high-beams.54732/page-2

 

[smurfslayer]

I think the responsive quotes / posts are these.

The relay is controlled by a coil; when you have your high beams on, current will flow from the headlight tap through the coil to ground.

A coil resists time rate changes in current similar to the way a mass resists acceleration.

If you suddenly open a circuit with a coil in it (flip to low beams), if the coil doesn't have an alternate path to flow current, the coil will produce a very big voltage across its terminals attempting to keep the current going (in particular, it's trying to maintain its magnetic flux), and in this case the voltage on the headlight tap side will be negative. Depending on the circuit, this could exceed 100V; if it were connected to a switch, it'll cause arcing across switches' terminals. A flyback diode give the coil a path to gracefully dump its energy into the coil's internal resistance.

The mass analog would be using your brakes instead of hitting a wall.

I don't currently know what's on the headlight side of the circuit; there could be a path for the coil to dissipate its energy gracefully.

Given that I don't know what's on the other side and given the cheapness of diodes I'm taking a careful route until I either get a schematic or hear from someone knowledgeable indicating a reason why it's a non-issue to run without spike suppression.

It is notable that there are some disadvantages to running a flyback diode; in particular, the relay will be a little slower to open and it's harder on the relay's contacts.

Shouldn't that 87a, (N.C.) actually be a N.O. contact 87?

Please see attached photo.
View attachment 128333 View attachment 128334

I don’t know if the pics from the above quote will come through, hopefully they do.

1st, know that @FordTechOne has warned us on numerous occasions not to do this (headlight triggering). I have no reason to doubt his rationale and he’s documented it previously.
2nd, I’ve done a similar operation but not equal with my b/d reverse lights circuit. In my case I wanted them on either with reverse OR with up fitter 6. Your method would be more complicated I think. I believe you could do a trigger from the headlight on condition OR up fitter switch by using 87 and 87a respectively for the triggers, and 85 going to the actual device- in your case, lights.
Again, this is not favored by @FTO, and IMO we should probably heed his advice here. Also, I can’t take credit (or blame ) for the reverse light diagram, I got it off another FRF member, did some internet searching to back stop it and tested it before putting it on the truck.

 

[dreys]

All done!

Now I have a set of SAE driving lights turn on when headlights are on, and set of DD Pro turn on when brights are on.

Headlights wire triggers relay #1 that is connected to AUX1, and brights wire triggers relay #2 that is connected to AUX2

 

[Oldfart]

All done!

Now I have a set of SAE driving lights turn on when headlights are on, and set of DD Pro turn on when brights are on.

Headlights wire triggers relay #1 that is connected to AUX1, and brights wire triggers relay #2 that is connected to AUX2

Please update if you have issues down the road.

 

[GordoJay]

What relays did you use? What was the activation current?

 

[dreys]

I've used a pair of 40 amp 4-pin relays that have been recommended for this application @ $7.36/ea
https://www.ebay.com/itm/4-PCS-PREM...SOCKETS-WIRE-HARNESS-BOSCH-STYLE/272925506047

On the headlight side, wire 7 is for brights, wire 8 is for low beams

It's been about a month since I had it done, I wanted to wait a bit to see if any issues come up. Nothing, the entire setup is working perfectly with no codes or issues.

I know @FordTechOne had an essay written on this topic, however in reality everything works just fine. It is so convenient too, I no longer need to reach to AUX every time I turn on headlights, or every time my high beams are on.

I've also turned on "bambi" mode in the Forscan, so now when my high beams are on, all 4 lights (2 OEM, and 2 DD) are all on. Makes a world of difference on dark roads, with a single flip of factory stalk. And I can keep my eyes on the road, rather than fiddling with AUX switches.

 

[FordTechOne]

I've used a pair of 40 amp 4-pin relays that have been recommended for this application @ $7.36/ea
https://www.ebay.com/itm/4-PCS-PREM...SOCKETS-WIRE-HARNESS-BOSCH-STYLE/272925506047

On the headlight side, wire 7 is for brights, wire 8 is for low beams

It's been about a month since I had it done, I wanted to wait a bit to see if any issues come up. Nothing, the entire setup is working perfectly with no codes or issues.

I know @FordTechOne had an essay written on this topic, however in reality everything works just fine. It is so convenient too, I no longer need to reach to AUX every time I turn on headlights, or every time my high beams are on.

I've also turned on "bambi" mode in the Forscan, so now when my high beams are on, all 4 lights (2 OEM, and 2 DD) are all on. Makes a world of difference on dark roads, with a single flip of factory stalk. And I can keep my eyes on the road, rather than fiddling with AUX switches.

Have you done an actual On-Demand Self Test of the BCM with ForScan while the relay is activated? There is no visual indication that DTCs have set. If you don’t find any DTCs, then the relay draw is most likely within the FET current draw threshold.

 

[dreys]

@FordTechOne - I have not, but would like to do that with both relays activated.

What are the steps in ForScan to run that test properly?

 

[GordoJay]

I've used a pair of 40 amp 4-pin relays that have been recommended for this application @ $7.36/ea
https://www.ebay.com/itm/4-PCS-PREM...SOCKETS-WIRE-HARNESS-BOSCH-STYLE/272925506047

I found a data sheet for the MAH-112-A-4R on the manufacturer website. It looks like the same unit. Nominal coil resistance is 90 ohms, so typical energizing current would be around 130mA. That's toward the lower end of current for automotive relays. I'd love to know how much margin you have.