When I got my 80 SS Royal Knight, the speedometer and tach did not work, the other four gauges seemed fine. The previous owner had swapped in a 350 and a four speed and the original speedometer cable wasn’t long enough. I took it to a speedometer shop and got a new cable made up, when I got it back, the oil pressure and temp gauges weren’t working.
Since I needed to tear into the cluster to find the tach problem, I researched the threads here on gauge clusters, tachs, etc. and tore into it. (Let me thank all the contributors again for some really great threads on this subject). My circuit mask had a couple of crossed “fingers” where it went into the connecter. That was my tach problem. I sprayed the mask and connector with electronic cleaner and gently wiped the mask down, and lightly cleaned the connector with emery cloth. I stabilized the connector as suggested in one of the posts (also cleaned all bulbs and sprayed the back side silver to make the lights brighter). I verified the continuity from the gauges to the connection fingers and the continuity of ground. I hooked everything back up and no change, I still have a temp gauge that won’t move off zero and an oil pressure gauge that reads 60 all the time! RATS….
Now the part that I need your advise on, do I assume that the mask is bad and replace it?
Since the gauges worked last week, I don’t think the senders are a problem.
Thanks in advance. :???:
Dave

Greetings!
Oil Pressure Gauge - Ignition On....Not Running....Ground the Tan connecting wire at the sender, your gauge should read Zero if it is okay. If the gauge does not drop to Zero when grounded, check for battery voltage at the Tan wire connector at the sender (the thing you just grounded). If you have full battery voltage then the Gauge itself is Bad. If you Do Not have battery voltage at the sender connector then the fun starts. Ignition OFF....Check for Continuity between the Tan wire connector at the sender and Pin 2 at the Printed Circuit Connector Plug (with the gauge cluster removed). If you look really close at the Connector Plug, the Pin numbers are marked on the black plastic plug. If you have a nice unbroken path from the Sender Connector to Pin 2 at the Circuit Connector Plug, then check for Continuity along the Pin 2 Printed Circuit tracing to the Gauge itself. If it checks okay, then you can check from the actual Pressure Gauge pins (where they come through the floppy Printed Circuit) to the "fingers" that would touch Pin 2 (from Sender), Pin 16 (Power to the gauges) and Pin 9 (Ground for the gauges). If the Printed Circuit is fine, then the Gauge is bad.
Next.....the Temperature Gauge.
Craig

Hello Again! On to the Temperature Gauge. Ignition OFF.
Remove the connector from the Temperature Sender on the engine block. Check the resistance across the Sender itself to the Block (make sure it is a clean Ground and not on paint). If it is Infinite or less than 40 Ohms then the sender is bad. (in normal operation the resistance will vary between about 1500 ohms cold and 60 ohms when hot) If the Sender checks okay, then check the Dark Green Wire from the Temperature Sender Connector to Pin 3 on the Circuit Connector Plug. If it has continuity, then check from the actual Temperature Gauge connectors (where they contact the printed circuit itself) to where the printed circuit "fingers" touch Pins 3 (would touch Dark Green connector in the Plug....the Temp Sender wire), Pin 9 (Black connector in the Plug...it is the Ground for the cluster) and Pin 16 (Pink/Black wire connector in the Plug....the Power for the gauges). In this last bit of testing what you are doing is checking the floppy Printed Circuit itself for good paths from each of the gauge's 3 terminals to the "finger" where it would mate with the Connector Plug. If all the paths check good, then the Temp Gauge is bad. However, since the Oil Pressure Gauge shares several of the same paths with the Temp Gauge and if there is a broken circuit path on the Printed Circuit, the Oil Gauge will read High (60 psi) and the Temp Gauge will read Zero (just like the sender reading Infinity resistance and showing Cold). I am betting on a crack in the tracing path on the Printed Circuit. I hope all of this makes sense to you...LOL
Craig (confusing America for decades)

WOW! Great inforormation Craig - thanks for taking the time and effort to write all that out for me (or "us", as I'm sure this will help many folks with similar questions).:You_Rock:
Dave

Great write up Craig, but I think when you ground the tan wire at the oil pr sending unit the gauge will peg to high and disconnected the gauge will show zero.
If I'm wrong I am sure lots of somebodies will exuberantly jump in to get in my s&&t.