Faulty light/dimmer switch? Need help.

[Hottytoddy06]

Good morning, all. I recently completed swapping a 6.0 in my square. Controlled by Holley Terminator X Max.. anyways the other night I noticed that I turned the key to the off with the headlight switch to the "on" position and the truck continued running. At first I thought I was crazy, but was able to replicate the issue again today. This is not always the case when the lights are on, but it seems when I turn/adjust the cab/dash dimmer switch the ECU is getting switched 12V power. I can even have the key in the off position, turn the headlights to the on position and adjust the dimmer switch and it will send power to the ECU. The high/low beam selector seems to work properly on the column.

The ECU (12V switched power) is controlled by it's own fuse/distribution block with relay triggered by the old pink coil wire coming out of the original fuse block.

Any thoughts or recommendations? I'm thinking bad dimmer/light switch.. I'm just not that familiar with the schematics of said switches.

Thanks for your help!

 

[Matt69olds]

Pull the dash light fuse, see if that eliminates the problem. If so, I’m guessing you have the ecm wake up wire on a dash light circuit.

If that doesn’t solve the issue, pull the taillight fuse.

You don’t need a relay to power the wake up wire for the ecm. It takes very little voltage and current to trigger a relay.

 

[goldpack]

I wonder if you could use one of these (something new, and different
than whatever is crossed from the new work. or just 40+ years old)

https://www.lmctruck.com/electrical/wiring-components/gm-heavy-duty-headlight-harness

for conversation of others:
what do you have in lighting / ignition that is 40 years old?

in lighting / ignition what do you have as new stuff (or parts or off a 6.0 donor) ?

 

[goldpack]

On a similar note. I am looking for some lighting pics/ videos of a 1986 column dimmer switch location.

I have been looking for Dimmer Switch videos,...plenty of them for swapping the older 70s floor mounted dimmer, but none that I can find for the 1986 variety.
(looking for it, but trying not to pry open fragile plastics that are intact more or less,...not sure if at the stalk,...under the dash at the base of the column). can't find it on any of the folios I can get hold of,
not sure if https://charm.li/ has it,...(zip file is out of service for download until Nov 1st, 2025,...the links hosted on our own board are a old 1985 book of descriptions but not pictured or described fully ).

not affiliated with this guy, but he does show the main light switch,...and discusses the swap and its issues / what happens to it as it ages, he does have a 86 like mine,...and yep fragile stuff he's not breaking.

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[edgephoto]

Are these what you are looking for? I had these from when I rebuilt my column a couple weeks ago.

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[goldpack]

Can someone Identify what this is that the screwdriver is pointing to. Not sure if it's oem gmc 86, or goes with the tekonsha 2030 mark 12 brake control. ...

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[legopnuematic]

That is the wiper delay module, oem @goldpack