98 GTP No headlights , common problems?

[LC-x]

Daytime running lights work
As soon as the light sensor detects dark conditions or you manually switch on the headlights , daytimes go out and there are no headlights.

Highbeams don't work when flashed either

Any common issues?

Thanks

[BNaylor]

Is that both low and high beams not working properly?

Common issue could be the multifunction switch (MFS) stalk.

[LC-x]

[
Ok now i have the full story ....

Daytimes- Only the orange markers work and when in dark conditions dashlights come on but no headlights (high or low)

The manual headlight switch only makes the markers/tail lights come on and nothing else

highbeams flash does not work, Very occasionally if i try highbeam flash they seem to work once or twice but if you try them again they don't work again.

[CrazyHorst]

I would first check fuses. I can't say whether the vehicle uses a heavy-duty manual switch or a relay somewhere. I would lean towards a relay because there's two "inputs" which are attempting to control the voltage to the lamps.

The "auto-on" circuit is a parallel "bypass" to the manual-switch (these are the two "inputs"). It sounds like "auto-on" is working correctly if it is turning the marker lights on.

With a 12v test lamp/probe or a DC voltmeter you should be able to check over the manual switch and see what's going on.

[BNaylor]

Make sure the headlamp circuit breaker hasn't popped located at the instrument panel fuse box. The one located by the glovebox. If you get the high beams to flash confirmed visually or see the the hi-beam indicator at the instrument panel (IP) you can skip this step.

The common point since your headlamps are not working in both low or high beams to include flash to pass and abnormal in both auto and manual modes is the MFS (dimmer-stalk).

Also, what do your fog lights do when you switch to high beams or flash to pass.

[LC-x]

I never thought to check what the foglights do when flash to pass.

But i seem to have all the correct feeds and grounds going into the DRL module and it clicks when turned on, but the blue wire (to the headlights) has no power. If i jump 12v to the blue wire the headlights work in low beam.

Another thing the flash to pass function of the MFS works fine when the ignition is off, but with ignition on it does not work. This is the reason i went for the DRL module, opening it up i realise its solid state so i have to find another one to check it.

[BNaylor]

I guess the DRL module is possible but how are you troubleshooting this? Are you using a meter (DMM) and GM FSM headlamp circuit wiring diagrams or justing hoofing it? I would be careful arbitrarily jumping stuff in that circuit.

What do you have at the dark green wire (pin D) input of the DRL module which is the 12 volt input from the headlamp switch via contacts in OFF?

When you jump 12 volts at that blue wire (pin E) DRL output for low beams all you are doing is bypassing the multifunction switch so that explains why you get the low beams when doing that. Also, you are applying 12 volts direct to the DRL diode which is forward biased to pass a positive voltage such as the 12 volts.

[LC-x]

The fog lights go on and off with the pass/flash on the MFS

[UKtech]

Then it sounds like the MFS is working , check you have all the correct inputs into the DRL , its the same one in all W-bodies.....and as stated above use correct circuit diagrams to diagnose