i installed a light bar in the grill of my 99. i want to connect the trigger wire on my relay to a positive 12v signal when the high beams are on. (so the light bar cycles on and off with my high beams). where can i find this a positive source at?
There's a white wire that comes from your light switch and goes to the headlight relay in the fuse block under your hood. Looks like you can tie into that.
no, a relay cant tell the difference between 10v and 12v, so the light bar will be on when the DRL is on.
what manbearpig said is right, the ground is switched on the high beams, not the 12v, and when the DRLs are on the BCM makes ~10v ground available
I think the high beam switch uses a state change signal to the BCM, so I dont think you can even grab it there.
I wired a 3 prong headlight to a 98+ headlight system and it took 4 relays and I couldnt get the DRL to work 100% in any configuration. I wish you better luck than I had.
Take a look at the purple wire connected to the high beam switch at E11. It's open until the high beams are turned on, then it supplies a ground through the DRL relay. Couldn't you connect a relay to that purple wire?
Joedoh, the ground for DRLs is supplied through the dk grn/wht wire on the left bulb. It basically runs the high beams in series putting a voltage drop across each bulb making them dimmer.
Kevinp1335, the purple wire has a positive or negative voltage on it depending on the lamps activated. You would need more support circuitry to make sure the coil does not interfere with normal operation of the system.
Joedoh, the ground for DRLs is supplied through the dk grn/wht wire on the left bulb. It basically runs the high beams in series putting a voltage drop across each bulb making them dimmer.
this explains why only one headlight would run as a drl with my 4 relay setup. it was very confusing, there should not have been a reason both lights wouldnt turn on, except as you say the lights were series.
I think the ground voltage is still actually lowered though, with no headlights installed and DRL on the ground voltage was around 10v (the positive was still at 12v). the one headlight that did come on for DRL (the left) was the lower DRL intensity high beam. the other light flatly refused to illuminate. in the end I left my 4 relay setup and disconnected the DRLs, which sucked because it really looked cool and old timey with that 7" round light having a yellowish glow. I fixed that on my latest truck by using headlights with separate low and high beams.
Ok, I believe I have figured this out. R1 only activates when headlamps are powered and R2 activates when low beams are powered, but since ground is cut off when switched to high beams, R2 will open and activate LEDs.
The BCM could be adding a resistive load through the high beam in input. I have no way of checking anymore.
My DRLs are long gone, I just got rid of my body relay block, and I'm hoping to get the passlock system tuned out of my PCM so I can just ditch the BCM altogether.
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