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

[4x4TruckLEDs.com]

So then there should be a code in the computer if that's an issue, right? If so i'll ask my buddy to run a scan on his truck. He has LVJ's system (like me) but he actually has his highs triggering his off-road lights.

 

[FordTechOne]

So then there should be a code in the computer if that's an issue, right? If so i'll ask my buddy to run a scan on his truck. He has LVJ's system (like me) but he actually has his highs triggering his off-road lights.

Yes, the BCM will set a DTC if it detects a fault. You will need ForScan or IDS to retrieve the DTCs.

 

[GordoJay]

So then there should be a code in the computer if that's an issue, right?

Not necessarily. If he's using a low current relay and the tolerance stack in the BCM is such that the relay doesn't cause a fault to be detected, he's good. For now. At the temperatures he's seen. It doesn't mean that it's a good solution for everyone because the electronic tolerances in every BCM will stack differently. A robust design shows no fault for any in-tolerance variation for components in the BCM combined with headlight tolerances, but is sensitive enough to detect faults in the headlight. The "wire stuff up, see if it works, sell it to customers" approach is flawed when you add modern electronics into the mix. What would be a wonderful thing for a vendor to sell(hint, hint) is a relay with a solid-state input circuit that draws only a tiny bit of current, less than one mA ...

 

[goblues38]

Relays don't use a "substantial" draw to trigger. That's why they are used everywhere.

I don't think you need to worry. I've never heard of anybody ever messing up any circuit on a vehicle using a relay.

Was just about to post the exact same thing. The trigger side of a relay (pin 85) causes virtually no impact to the system.

Would be very simple to connect pin 85 of the relay to the bright light wire near the headlight. Use this to switch 30amps fused to another circuit to power the lights.

Or go one step further and include another areaway to make it so the uplifter switches can kill that functionality and another relay to still allow the uplifter switches to work on their own.

I used to love all the stuff we would do with relays back in the late 80's when car audi and security were just getting off the ground.

I worked with a guy who had is entire bronco automated with a relay back of like 10 relays. click clack was so loud, but cool.

 

[4x4TruckLEDs.com]

LVJ has this built into their relay system. They have a "kill" or "override" that de-activates the "high beam trigger.

 

[smurfslayer]

The draw from the relay doesn’t need to be “substantial”, it just needs to be enough to exceed the BCM’s pre-determined threshold for current draw. That threshold depends on the factory load that the FET is driving. Once the the threshold is exceeded, the BCM will set a DTC against them circuit. If the over current condition reoccurs, the BCM will shit down the circuit. If the fault continues to occur, the BCM will eventually permanently disable the circuit output.

quoting this for posterity. It keeps getting asked and answered in the disparate threads.

The "wire stuff up, see if it works, sell it to customers" approach is flawed when you add modern electronics into the mix

^^^^ Clueful.

What would be a wonderful thing for a vendor to sell(hint, hint) is a relay with a solid-state input circuit that draws only a tiny bit of current, less than one mA ...

Even then, you are still drawing some amount from the lighting circuit to signal the relay. Probably less so than a mechanical relay, but it’s there. As your clueful sentence indicated, we’re doing this kind of activity without full understanding of what the BCM will tolerate vs when it will throw a DTC, and... when it might scram.

 

[GordoJay]

Even then, you are still drawing some amount from the lighting circuit to signal the relay. Probably less so than a mechanical relay, but it’s there. As your clueful sentence indicated, we’re doing this kind of activity without full understanding of what the BCM will tolerate vs when it will throw a DTC, and... when it might scram.

True. Ford won't share design info, either. But we have some clues. Some people manage to run some relays some of the time without causing a problem. The lowest current automotive relays draw about 50mA or coil current. If we choose a relay with an input current about 100 times lower than that, we should be safe almost all of the time. Yes, almost. If you brick the BCM and Ford sees the relay, it won't be covered under warranty. And all car manufacturers overcharge horrendously for electronics modules that cost only a few dollars to make. So it could cost you big. Now, if someone made a relay with a MOSFET input, it would draw 100nA(0.0001mA) or so, which would be swamped by the tolerance stack and should work 99.999% of the time. I'd be very comfortable installing that in my truck.

 

[GordoJay]

If someone packaged one of these https://www.diodes.com/design/suppo...-harsh-environment-of-automotive-applications with an automotive relay, you're looking at 0.12mA activation current. That should be entirely safe so far as bricking the BCM goes.

 

[smurfslayer]

The lowest current automotive relays draw about 50mA or coil current.

from the relay trigger connection? that much?

 

[FordTechOne]

Not necessarily. If he's using a low current relay and the tolerance stack in the BCM is such that the relay doesn't cause a fault to be detected, he's good. For now. At the temperatures he's seen. It doesn't mean that it's a good solution for everyone because the electronic tolerances in every BCM will stack differently. A robust design shows no fault for any in-tolerance variation for components in the BCM combined with headlight tolerances, but is sensitive enough to detect faults in the headlight. The "wire stuff up, see if it works, sell it to customers" approach is flawed when you add modern electronics into the mix. What would be a wonderful thing for a vendor to sell(hint, hint) is a relay with a solid-state input circuit that draws only a tiny bit of current, less than one mA ...

All great points Gordojay (subsequent posts as well). A solid state relay would be the ideal solution.