never2much

Hi Jim,

Could you post up Sheet AD 22, I noticed that on the 91 wiring diagram (Sheet 21) the headlamp switch's switched ground also has a circuit that goes to the snow plow provision on sheet 22. On the 93 wiring diagram that circuit is shown as going to the tachometer provision.

Maybe what we are missing is on that sheet.

Jim Lane

Ok,
Here is AD-21



Here is AD-22



Jim

j_martin

I would think that if the DRL module output is wired to the headlights after the relays, and the parking light circuit is still going to the DRL, it should work normally.

In theory, if the headlight switch is off, the DRL module uses a few inputs to supply the headlamps with a lower voltage to dimly light them. As soon as the headlamp switch if moved from off, ie parking lamp circuit is energized, the DRL shuts off and lets the normal circuitry run the lights.

It should work if you move the wires that run from the DRL module to the left headlamp connector to the same location on the connector now on the headlamp that's powered from the relay mod.

In my 93 diagrams I notice that the DRL module is wired to both high and low beam circuits at the right headlamp connector. The SM doesn't have squat for theory, other than the DRL module lights the headlamps at less than 50% brightness. I'm guessing it lights both filaments at about 6V.

I'd bet it wouldn't light LED's at all. In that case you could wire the DRL module to bumper or grill mounted running lights.

never2much

Jim,

I spliced into the steering column wiring instead of discounting it as you suggest and it everything worked. However, the low beam trigger wire needed to be disconnected, as it caused the relay to chatter.

mpatl

Thanks for posting the wiring diagram, I marked it up here for clarity. This is how I got mine working on my truck. You don't need to go digging in the truck cab for wires with this setup. All the signal you need is at headlight harness.



A relay setup will not work until you separate the DRL wires from the passenger harness, the pulse width modulated drl voltage will buzz the heck out of the relays. Since it is all taped up, the easiest way is to cut both reds and both purple wires (the pairs going to the high beam and low beam on the connector) and test. With the truck not running (so as not to activate the DRL module if you just moved it), with the low beams on, mark which purple wire has 12v. With the high beams on mark which red wire has 12v. The other two wires are by elimination the DRL wires.

Now proceed to build your relay harness like normal. When done, wire the DRL wires to the headlamp side of your relay harness. So just like the stock setup, one of your headlights will have 5 wires going to the harness. A ground, a high and low beam from your relay power, and a high and low beam from the DRL module.

Now when the lights are on they go through your relays. When off, the DRL module powers the lights as it always did with PWM voltage to get dim driving lights.

thrashingcows

Sweetness! Thank you for taking the time to update this thread....always appreciated!