Gauge questions

I've read a lot of threads on gauges and I am trying to narrow down a way to go about troubleshooting. My oil pressure gauge reads 45 psi. My voltage gauge (engine running) is 17v. My temp gauge (engine warmed up) reads 145*. My gas tank gauge reads at about 2 o'clock. I know that there are no resistors on the back of the gauges. Should all the gauges have resistors installed behind them?

I received 2-5w 90 ohm resistors today. Should I install them on the fuel and voltage gauges?

I would start out by ensuring the gauge cluster is properly grounded. On older trucks it’s a black wire grounded to a post on the emergency brake mechanism, and on newer trucks there is a ground bar/ ground point mounted up under the dash above the pedals.

Then start checking the wires to each sending unit. For example, ground the wire for the temp sensor and the gauge should read full hot. With high resistance (3k ohm?) it will read low and with your 90 ohm resistors it should be about 240-250 degrees. However, GM changed the gauges and senders over the years, so yours may need a different sending unit to read correctly.