Hey guys my headlights won’t turn on , the fuses up the dash are all good & all wires seem alright . And when I pull back and put it on high beam they work but that’s it . Any ideas how to get them to work please would be a big help thanks
Joined: Sat Oct 06, 2012 5:49 pm Posts: 1975
Vehicle: Sierras!! SWB and LWB
Posted: Wed Jan 02, 2019 6:05 pm
A few questions to help
Have you checked the bulbs?
How have you checked the fuses, it’s unlikely but they can break without the usual signs. Continuity check with a multimeter will tell you for sure, alternatively replace the fuse. They’re cheap and it’s an easy way to be sure.
Do you have a multimeter? Check the voltage at the plug at the back of the headlight. Then check and see if it has an earth. If you’re not sure how to do this then sing out, we should be able to help
Joined: Sat Oct 06, 2012 5:49 pm Posts: 1975
Vehicle: Sierras!! SWB and LWB
Posted: Wed Jan 02, 2019 8:25 pm
Ok, just gazing at the wiring diagram. It’s a process of elimination and I reckon there’s a lot more info you can give to help us narrow down the problem.
You say when you pull back on the stalk (switch) you get high beams come on, that’s called pass signal. If you have the headlights on and you push the stalk (usual high beam) do the high beams come on then?
Also does the high beam light on the dash come on with either or both? Or not come on at all?
R/W (red with white tracer) wire into the right hand headlight, and W/Bl (White with Blue tracer) wire into the left hand plug is constant 12v +ve.
I reckon if you check the R/W and W/Bl wires at the headlight plug you’ll find 12v is there. If there wasn’t the none of the lights will work, you said the high beams work when you pull the stalk.
If I’m correct and you have 12v there, that excludes everything upstream being the problem. So your power supply from battery is fine, your fuses are fine and the wiring up to your headlights are fine. The problem is downstream.
If you have both normal high beams and pass switch high beams then the problem is downstream of your low beam circuit. That is from the Red/White wires to the -ve terminal of the battery.
If you have pass signal high beams but not driving (normal) high beams then the problem is likely the dimmer switch.
Disconnect the negative terminal of the battery. Test from the Red wire at the headlight plugs earth (not the negative terminal of the battery because you’ve disconnected it) for continuity with the stalk in both the driving high beam and pass high beam positions. Tell us which one or if both have continuity.
You’ll need a multimeter for this, if you don’t have one then a cheap one from auto or electrical places will do.
Last edited by bumstein on Wed Jan 02, 2019 8:51 pm, edited 1 time in total.
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