SOHH the gauges in my El Camino work intermittently

[Flipper_Purify]

I have an '86 Chevy Elky. The cluster of small gauges (temp, oil pressure, fuel, and battery) works intermittently. My mechanic told me that the head unit is broken. I'm thinking that it's just a loose wire, because speed bumps make it work again, or not work again.

How can I solve this myself? I don't wanna take it in to the shop, and they do unnecessary work.

[The Bilingual Gringo]

When it comes to electrical problems, especially on older cars, there's usually no choice but to take things apart and go digging yourself, or pay someone to do it.