Replacement gauges
 

I replaced the gauges in my Bombay Clipper. The new gauges are reading incorrectly. Do I need to get the replacements from Moyer or how do I correct the readings on my current gauges?

The sending units are not compatible with the gauges. You need to replace the sending units with ones from the same manufacture as the gauges. There are some "universal" sending units; I don't know what they are or if they would work with your gauges.
What brand of gauges did you buy?

ex TRUE GRIT

Welcome to the forum

Edit: Also resistance in the wiring sending unit -> gauge will cause false readings.

Most USA standard sensors are 33-240 ohms. If the sensor and gauges are both 33-240 ohms units, the 0 to full scale will still work. The tricky part is the range, a 0-80 PSI sender on a 0-150 PSI gauge will show 75 PSI when it really is 40 PSI. Hooking temp to oil pressure and vice-versa will give nonsensical results.
In the case of old unknown senders that may have issues and perhaps no one knows the ranges, it is easier to get them all as a package ;)

Thanks John and Joe! The gauges that I purchased were Sierra Gauges from Defender Marine. I bought the heavy duty gauges. Would either of you know about the sending unit that I would need. Sierra is only showing a unit for 80 psi dual station oil pressure.

I am 99% sure Sierra is all 33-240 ohm, so most standard senders will work. The dual gauge sender will NOT work right with only one gauge hooked up to it!
Moyer sells appropriate senders usually, but they seem out of stock right now. This one from Amazon would do if you need it right now:
https://www.amazon.com/Sierra-18-589...1386259&sr=8-3

Or here:
https://www.fisheriessupply.com/sier...enders-18-5899

You could call Moyer and see if they have any, the website shows sold out.

Defender has these that would work:
https://www.defender.com/product.jsp?id=1566892