Cluster lights mystery

Howdy all - Looking for some brainstorming help with my 86 2.0.

I'm having an intermittent issue with the warning lights in the cluster - turning the key to the on position, I'll get the seatbelt chime and light, but no other lights (battery/oil/egr/etc). After starting the truck, I'll have a faint glow from the charge indicator light.

Sometimes, turning the key on, everything works as expected (warning lights come on, then go away when the engine starts, etc).

Truck starts and drives great.

Alternator is working fine (seeing 14+ volts when running). Everywhere I've tested voltage with the key off looks good - 12.75v or so. I'm assuming there's a voltage drop somewhere prior to the cluster though. I'm just stumped on the intermittency. I've replaced all the fuses and cleaned the fuse folders, plus any other connectors I can access. I can't seem to make the condition change with any wire wiggling.

Any suggestions on where to look from here?

Update: discovered that if I give the dash a good thwack right above the cluster, the problem goes away. Thoughts?

It will either be one of the harness sockets going into the back of the cluster or the circuit board on the cluster is suspect.