Blinking headlights

[donut]

Vehicle in question is the '86 C-30 in my sig.

When I turn on the headlights, they start intermittent flashing. They'll come on for about a minute, and it seems when they "warm up" they start flashing. low beam, and low-high together. Marker lights and turn signals appear to be fine, the flashing doesn't effect them.

I have changed the light switch, (sight search seemed to indicate this could be a problem). I have cleaned any grounds I could find, and traced wires from the firewall to the last light in the chain and found no breaks, nicks, burn spots etc.
It'll also do it if all 4 headlights are in or just 1, no difference.

Truck has been like this for a few months and now I'm at wits end. On top of it all, I'm not sure which direction to proceed.

Nothing major electrical has been done to the truck just years of neglect.

[VetteVet]

According to the wiring diagram I have, your headlights are fed by a yellow wire from the headlight switch to the high-low dimmer switch. It doesn't show any relays but there are probably two of them. I don't know whether the dimmer switch is on the floorboard or the steering column but if your yellow wire is making a good connection at the headlight switch then I would suspect the connection at the dimmer switch, or a bad switch. The relays could also be cutting out after they get warm.

this is the 86 with the yellow wire and below is the 85 with the light blue wire.

[donut]

Thanks for the diagram, much easier to read than the one in the Haynes manual. (don't even need the magnifying glass, lol)

Dimmer switch is on the column and it's been replaced. I do suspect it's the relays getting hot (one in the headlight switch that I know of) Switch does get a little warm, but not hot. Just enough to question it. The switch connections looked clean, no obvious signs of burning.

While typing this, sometimes I just need to jog my brain a little, I think I'll try to disconnect the rear lights and take them out of the equation. It did have a trailer connection that was all corroded and busted up, maybe there is a cut wire somewhere back there. This post reminded me that before I "fixed" the rear lights, the fronts worked. It's been several months, so my memory may not be the best.