I have weird problem with the passenger side low beam headlight on my '01 Dakota. A couple weeks ago it started flickering, then progressed to turning off a few minutes after I had turned the lights on. I discovered that if I activated the high beams, then went back to lows, it would work again for a few minutes then go out again. Now it won't work at all, although all the other lights on that side work. Changing the position of the steering wheel makes no difference either.

I have tested for power at the plug, and there is none there for the low beam wire. Fuses are all good. What should be my next step? Do I have to undo the wiring harness and try to trace back to find a possible break in that one single wire? Or is this more likely in the power switch or dimmer switch.

 

You can rule out the headlight and dimmer switches. Both headlights are on the same "sense" circuits. The headlight switch and dimmer do not directly control power to the headlights - the CTM does.

First thing, check the headlight grounds. G112 is used for the passenger headlight, it is located on the RH fender front just behind (engine side) of the radiator support and near the cruise control servo.

But, since you say you don't have power at the plug I'm thinking the CTM itself may be the cause and it is a common failure.

 

I had a problem with my turn signals that turned out to be a junction plug under the truck that was bad. I direct wired everything and resolved the issue. Not saying you have the same type of problem, but see it there are plugs along the way between the headlight and other parts of the truck. May not be but worth a look. 00DakDan knows more than I do so I defer to his knowledge, just offering a possible easier fix.

 

Thanks much Dan. That is a relief about the switches. I have done practically nothing with wiring on vehicles, so don't want to get more involved than I have to. But I'm curious about how the wires run to and from the power switch and dimmer switch to the fuse box and then to the lights. Where do they split to go to each light? At the fuse box?

I will check the ground, but wouldn't the high beam also fail if the ground was bad?
Also, forgive my ignorance, but what does CTM stand for? Assuming something, something, module. What does it look like and where is it located.

 

Here you go.

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CTM = central timer module.

Thank you Magnethead for posting the schematics. Big, the feed for the lights is direct from the CTM. No switches involved.

Check the bulb too. Who knows, maybe the filament is doing something weird.

A bad ground can still be intermittent. It's cheaper to fix than replacing the CTM which may ultimately be what you need to do.

 

Ok, I am very confused now.
I checked the ground, seemed tight and good, but disconnected it and just to double check, turned the lights on. The lights all worked as before, no low beam, even though the ground was disconnected. What??????

Also took out the CTM and cleaned it gently with baking soda as I saw someone else had done, but it didn't work for me.

My father-in-law had an 01 Dakota and ran into a similar issue. He ended up just running a wire from the working driver's side to the other side of the truck and that fixed it. Any reason I shouldn't try this rather than spend the money for the CTM?

 

are you sure you pulled the right ground? Each corner lamp assembly has it's own ground as shown above- 113 for driver and 112 for passenger. 113 is also the ground for all of the taillights (strange but whatev)

You could run a jumper but it might eventually overload that driver circuit. Not sure why they couldn't just use relays from the factory.

G112 "right fender side shield", 10mm nut next to access opening
G113 "Near Battery", 10mm nut next to the access opening

Can you backprobe the connector at the CTM for a signal?

 

Yes I am sure. Only one on that side of the truck that any wire from that bundle connected to.

 

All I can think of is that it somehow grounded through the high beam wire.