Got an 84z and my tach and oil pressure gauge hasn’t worked since I’ve had the car. The tach did bounce sometimes at certain speeds but it would eventually just peg out at 7000. And the oil pressure gauge pegs all the way up. Well I bought a new board from Cajun Tach with the LEDs and installed it and the red LED light does come on to signal power to the board and the green LED light he put on the board also lights up to signal the board is getting RPM signal. All other gauges work. Well, the tach now just stays pointed down at all times and the oil pressure gauge still pegs up. I have replaced the oil sender and it didn’t fix it. I haven’t followed the wire to see if it’s corroded or damaged so I was gonna look at that soon. But what could make the tach still not work? It’s getting power and signal? Any ideas? Thanks.

 

I recently solved the problem of my tach stopped working. It turned out to be a bad wire on the tach filter. It works perfectly now.
Try temporarily connecting it without the tach filter and see if it works.
If it's already getting a signal from the distributor but still reading zero, I would suspect you got a defective board from Cajun.

The oil pressure gauge requires grounding to read zero. Your wire or connector could be bad. And yes, it is entirely possible these days that a new sending unit could be bad right out of the box. Touch the wire to the engine and turn the key On. The gauge should immediately move to zero...