Gauge issues. 85 C10

[Zach079xxx]

I've posted on here about my gauges before but no luck, so lets try it again.

Working gauges

1 - Clock
2 - Speedo
3 - Gas (after new sending unit was installed)

NON-Working gauges
1 - Oil pressure ( pegged )
2 - Temperature ( pegged beyond max )
3 - Volt ( Also pegged )

Heres my baby, last week at a car show / parade
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Off topic, but I also made some custom armrest trim too! What you guys think?!

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Guessing its a bad ground, but I have no idea where/how the cluster grounds. Can I add a manual ground, like some sort of wire..? Ever since I've had the truck the gauges haven't worked. I installed a set of mechanical gauges 3 days ago, but I really want my cluster to work. And honestly, if it is a ground, I hate to drive it knowing it could go downhill and burn. What should I look for? What color wire, if it is a wire, is the ground wire? How hard is it to remove the whole cluster without screwing up the speedo cable and all that goodness..

Any help would be greatly appreciated, thanks guys.