Let’s slay this dragon…

[Jgonick]

Should both door switches have 2 wires connected to the switch? Driver side had 2 but passenger side only 1.

White wire is ground- both sides should have one. Tan wire is for key left in ign ground (warning ding) - only on driver side.

 

[Jgonick]

Likely a broken wire under carpet drivers side.

Orange wire is taking power to dome light. White wire is ground coming back- it is spliced somewhere slightly above the fuse box with the white wire running to door jamb & to courtesy light. From courtesy light the white wire (sometimes changes to wht/blk) runs to light switch to ground it when you twist the pull knob.

The orange wire (I marked in attachment) coming out of the fuse box should meet up with the white wire and head back down under the carpet.(also marked on attachment)

So if your courtesy light is working- it gives you an idea where the problem might be. Like @fast 99 mentioned- very common for it to be broken under the carpet.

 

[ajdouble]

The circuit has to be complete for the light to burn. if schematic is not helping try working from the receptacle to the point of power. broke wire makes sense. Ohms law comes to mind.

 

[wildgoose]

Orange wire is taking power to dome light. White wire is ground coming back- it is spliced somewhere slightly above the fuse box with the white wire running to door jamb & to courtesy light. From courtesy light the white wire (sometimes changes to wht/blk) runs to light switch to ground it when you twist the pull knob.

The orange wire (I marked in attachment) coming out of the fuse box should meet up with the white wire and head back down under the carpet.(also marked on attachment)

So if your courtesy light is working- it gives you an idea where the problem might be. Like @fast 99 mentioned- very common for it to be broken under the carpet.

Thanks. The white wire from that orange/white pair does in fact run behind the fuse box to above. I can’t see where it goes but assume either the door switch or it’s open ended. There are no courtesy lights installed in this truck.

I also noticed in the owner manual that the clock and dome light is on the same fuse so pulling that fuse today to check it before I pull out seats and carpet.

 

[Jgonick]

I pull out seats and carpet

You shouldn't need to pull out seats. It will run down the side by the driver's door. Usually taking the plastic piece off the lower door jamb is all you need to do to peel back the carpet to see.

 

[Steelbuddha]

This is the Painless Wiring manual for their big-ass 27-circuit harness. It's an excellent reference and explains a lot of stuff: https://painlessperformance.com/wp-content/uploads/2024/02/90627.pdf The color codes are all consistent with original.

I installed one of these in my 1984 K-20 and all electrical problems disappeared.

Re: your question about the green wire, are your reverse lights working?

 

[olnick]

here is a wiring diagram:

X8430_1984_GMC_CK_Light_Duty_Trucks_Wiring_Manual

MediaFire is a simple to use free service that lets you put all your photos, documents, music, and video in a single place so you can access them anywhere and share them everywhere.

www.mediafire.com

I have used this site for at least 10 years now all the downloads are OEM manuals
This will get you out of trouble!!

 

[molus]

Here’s a link to all the wiring diagrams. I printed them out to make life easier.
81-87 cab interior pg1
81-87 cab interior pg2
81-87 chassis and lighting
81-87 front lighting
81-87 v8 engine bay
81-87 instrument panel pg1
81-87 instrument panel pg2
81-87 ecu wiring.

 

[wildgoose]

Alright, alright, alright… on today’s episode of “sh!t you can’t make up” I decided to remove all of the upside down or blown fuses with those nifty blow glows. Figured since the battery is at least 3 years old, may as well pick up a new one. Good to go, right?

What are the frickin’ chances… my voltmeter gauges is now reading 8 volts during the drive home. Cause I was really wanting to stay up and install a battery late at night.

New battery installed. Volt gauge reads 10 with key in the on position. Is that a normal value? Old batt measured 12.3VDC with a meter on the bench and new is 12.6.

 

[ali_c20]

I throw in Volt gauge ground.

 

[wildgoose]

I throw in Volt gauge ground.

I might agree with you but I should’ve said it was reading 8 volts but also varying up and down with acceleration and dropping below 8 with window switches operating.

 

[wildgoose]

Update… alternator was only outputting 11 volts after the new battery was installed. Should’ve known this would turn into a two for one special. New alternator going in now. Just finished priming and painting the thru bolt bracket since it was covered in grease/dust.

As an added bonus… the plastic wire loom that was covering the alternator harness melted to the intake manifold, directly on the EGR blanking plate. The plate cracked near the thru hole so some steel stick putty is nearly cured to drill and reinstall that little widget. Explains the truck sounding and running like crap the last few days.

Fun times.

 

[wildgoose]

Alright so finally got back to one of the original objectives… the pesky dome light. I traced the wire under the driver side carpet. Found no cut wires (but did find some spot rust) and cleaned the connector behind the speaker. After reconnecting, I tested and got 12 volts at the wire before the speaker box. So power is somehow finally making it to the light. Cool. Inserted a bulb and the light worked. The passenger side door switch grounded properly and the light went out. However, shouldn’t the light have stayed on if the driver door is open?

 

[wildgoose]

Further… the dome light also works now when the headlight knob is rotated full left and past the click, but it still won’t turn off when the switch is depressed. Switch tested good for continuity, as expected since it’s brand new.

 

[wildgoose]

These are the wires coming through the door switch hole. White wire is carrying 12V. Brown wire has nothing and fails continuity test. I can’t tell where it goes after the door. There is a similar brown wire going from fuse panel to the left side fuel tank but I’m assuming I’ve followed the wrong wire during my tracing.

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