Temp gauge issues

[PharmD]

Sorry to bother you guys reviving an old thread, but I have been following a couple of these threads trying to solve my temp gauge problem. I have a 98’ Chaparral 2130 SS with a Mercruiser 5.7L carbureted Thunderbolt. SN: L056178. When I bought it, the temp gauge didn’t work. I tried grounding the sending wire and got nothing. I tried grounding the threads on the sending unit and still got nothing. I removed the temp gauge and tried to put power to it using a 9V battery and got nothing. The light in the gauge wouldn’t even light up. I went to O’REILLY auto parts and bought an Iequus temp gauge that most closely resembles the original guage. It has three prongs on the back. One says “S”, another says “+” and another has some kind of symbol resembling a sensing unit. When I hook the tan wire to the “S” and the purple wire to either of the other 2 prongs, it pegs all the way hot. If I ground the sensor wire at the motor, the needle goes down. It’s completely backwards. I’m at a loss because I’m not very electrically inclined and I am not sure what to do from here. Any help would be greatly appreciated. Thank you so much for your time and help

 

[Candy Gramformongo]

Instructions for installation are here link. Tan is standard color for sensor, connect to S. Purple is standard color for 12V ignition on, connect to +. The symbol you say looks like a sensor is actually a ground symbol. Find a way to ground that terminal, there is probably a black wire available for that. Now when you ground the sensor wire at the engine, it should peg high.

 

[tank1949]

There are differences between temp sender and switch. The sender must be compatible (ohms) with gauge display at helm. The switches, not so much... Also, do not use excessive Teflon sealant on threads. Excessive tape reduces grounding. My boat's former owner had some crazy wiring too. I could never find switch leads going to helm. I had to run separate wires from helm alarms (hot side) to switches.