Brake/ parking light issue

[Haybag]

Have a newly acquired 72 k20 with an electrical issue. When I press the brake pedal the left front parkinglight , marker light and left side directional dash light illuminate. All other lights work properly. Checked bulbs, but does it with taillight bulbs removed. Cleaned up taillights mounting surfaces and ground wires ,but no luck. Any ideas where else to look?

[jocko]

By grounds, I assume you mean the whole light harness grounds, not just the fronts? The rear grounds are common culprits. If you checked all the grounds, time to start unwrapping the black tape and looking for a short. I'd check and re-check the grounds first though, with focus on the rear tail lightgrounds. It's often worth the time to make temporary grounds from the taillights to the frame just to try to figure out where the problem truly lies. Can do this with a long wire w/alligator clips. Whatever you ground, if it works, then you can focus on fixing the actual ground, or adding a ground wire, if needed.

[Steeveedee]

It's likely in the turn signal switch. Brake light and turn signal wires get separated there, and if the one wire from the switch to the left front is making contact with the wire for the rear, those lights mentioned will light up. That separation is just so that the front marker and turn signal don't light up when you're only using the brake.

[Haybag]

Cleaned up grounds and everything was working, took it for a drive and acted up again, but by the time I got home they were working fine again, will have to check the turn signal switch.