New to forum: Have a 1986 C30 Light issue sat from 2008 untill now!

[SFR7771]

I'm having a lighting issue on my 1986 c30:

    Working: Headlights, front blinkers, cab lights, and the left rear blinker.

    Not working: Tail lights, marker lights, dash lights, and right rear blinker.

    I’ve checked all the fuses, wiring, the fuse on the red wire under the hood, and the wire block.

    I’m also getting no power at the 5-pin trailer connector in the bed.

Is there anything else I should check? I’m trying to get this fixed before driving to the C10 Nationals tomorrow.

[Captkaos]

Are you getting power at the rear light sockets? power at the cluster connector?  Power at the rear light harness connector?

[bd]

You didn't mention whether you checked for the correct bulbs and the filament integrity.  Verify the lamp grounds and ensure the bed is grounded to the frame.  Check the wiring harness for melting, abrasion, pinching, and/or severing where it passes over the rear axle near the exhaust pipe; the harness plastic retaining clips fail, allowing the harness to sag or fall away from the frame toward the exhaust.

Regarding the dash lights, see Diagnosing Inoperative Dash Instrument Lighting.

For reference: 1986 GM Wiring Manual

[SFR7771]

No power at rear on anything but left blinker, no power marker lights. Bulbs are correct...

[bd]

Verify power on the rear lamp wire harness where it exits the firewall bulkhead connector along the driver (left) side of the connector.  If you have power there the fault is rearward.  Typically, the rear lamp wiring runs through corrugated loom along the left frame rail.  Wire damage/separations can be difficult to locate when hidden inside the loom.  Be patient.

If there is no power through the bulkhead connector, use the diagram of the headlamp switch connections (previously linked) to test power through the pins of the switch.

[SFR7771]

Thanks much appreciated

[bd]

Sitting for that long the problem could be rodent damage.

[SFR7771]

Suprizingly, the truck is solid, and all wires are in tacked no signs of and chewed up wires...

[SFR7771]

Did some testing on the rear wires out of the left driver's side block with not much luck, traced wires over tank and lost them, but everything looks solid.

How big of a part does the light switch play in all this wiring issues?

[bd]

As long as power reaches the headlamp switch, it distributes that power to the various running lamps (except for the brake/turn lamps, which are powered through the turn signal switch).  The headlamp switch has two power inputs: one strictly for the headlamps via a fusible link, the other for all the running, dash, and cabin interior lamps via the fusebox.  The issue is probably inside the cab if you don't have power through the firewall bulkhead connector.  Verify power to the headlamp switch, then check power on each switch terminal.  If the switch operates properly, move to the wiring between the switch and the bulkhead connector.  Follow the links I provided; all of the information is there.