My dash has a sweet spot between the center vent and the little vent for the temp sensor which, when you whack it just right brings my instrument lights back to life for a few moments, then repeat as required.

Now, is there a goofy ground or something right at this one location?

Seemed odd that power comes back from hitting a spot so far away from the instrument panel itself..

If nothing is loose then check for shorts against sharp edges on a harness. Failing that I fear a fractured wire in a harness.