So my new-to-me '01 1500 everything works as it should with the interior and electrics- except the high beams. When you pull the stalk for brights the fuse in the "parking light" socket instantly blows. Low beams and parking lights work as they should (even with the park light fuse blown). There is no high beams or indicator. Both the L and R headlight fuses are fine.

I probed the park light fuse socket and did find a very low resistance circuit to ground when the high beams are turned on. Not purely shorted, reads like 70 ohms, but plenty to pop the fuse instantly. I tested the multifunction switch per the shop manual, and it seems to check out, at least it is connecting the pins the manual says it should, although I suppose it could be shorted internally and also connecting to ground.

This truck does not have factory foglights. The "quad beam" fuse sockets are empty (no terminals), and the "quad high beam" relay socket is also empty. Far as I can see the wiring underhood is unmolested- no evidence of cobbled in aftermarket lights or anything like that to blame spotty wiring on. Headlight connectors and harness all look completely original, and the bulbs check out also.

I read a suggestion here about wires chafing along the steering column so removed the column shroud and the kick panel. I see see one wire from the multi switch (a solid blue) that had a wrap of tape around one spot, and under that it looked like it had rubbed through or got pinched, the insulation was scrunched up exposing copper and someone already hastily repaired it. I cut the damaged bit out and used a sealed splice connector for good measure. I inspected all the rest of the wires and didn't see any other evidence of damage, it all looked 100% original. No random splices or anything for prior accessories or mods. They were all routed through a plastic guide sleeve clipped to the column.

Any other thoughts of where to check/look? A new MF switch isn't terribly expensive aftermarket, or I could go to the local pick-a-part and steal one off a junker, but I hate to just throw parts at problems. All other functions on the stalk work as they should. I read there's a lighting control module or something behind the dash that can go bad, any real way to test this? Or just "replace with known good" as seems to be the diagnosis for most computer modules?

 

with dtrl lights as not? sure which diagram to use

to clarify: the park lamp fuse f blow when you turn on the highbeams even though the headlights are on their own separate fused circuits fuse c and b?

 

No, this truck doesn't have DRL's.

Yes, the park lamp fuse blows as soon as you pull the stalk for high (does now blow if you just turn on low beams). The L and R headlight fuses do not blow. Yet, the parking lamps all still work properly whether their fuse is blown or not.

With the switch in high beam position, the headlights are off and no high beam indicator. The taillights and parking lights are still on. Pull the stalk again and the low beams return.

 

their should be no connection in the park and headlight circuits .....to test...disconnect the battery...remove the park fuse f, headlamp fuse c and b...do an ohms check across the park and healight fuse pins(you must be on the side of the fuse pin that leads to the switches).... with the dimmer on high and headlight switch on....should be open/no continuity. if you have continuity...shut off the headlight switch and recheck....then dimmer on low and recheck. post back the results and we can go from there.

 

Thanks, I'll give that a try tomorrow and see what happens.

 

The only place where the parking light and headlight circuits are somewhat close are at the headlight switch. That's another spot to look at, could be the switch internals, or maybe the wiring connector. What makes this worthwhile to look at it is that the switch works by connecting the headlight bulbs to ground but the parking lights get 12V from the switch. So there are +12V and ground connections present at the switch.

 

its a ground controlled circuit
power goes from the fuse to the headlamp at all times....the switch provides the grd to complete the circuit. to me this says everything before the switch is fine...or else it would blow regardless of the switch position.

 

Agree, and I'm somewhat puzzled that the low beam circuit seems fine while high beams cause the issue. Downstream from the multifunction switch there's only one wire going to the headlight switch.

OP: Try to remove the headlight switch and jumper the connector for the parking lights and the headlights. If the issue persists it's not the switch. It also gives easy access for using a multimeter.