Greetings and welcome aboard the CF, jpgriffin.
Testing Temperature Gauges:
1. Disconnect Tan Sender Wire from Gauge (Terminal “S”) and turn Instrument Power ON.
The Temperature Gauge should indicate ZERO Scale (< Low Temperature).
2. Short the Gauge Sender Terminal “S” to Ground Terminal “G”.
The Gauge should deflect to FULL Scale (> High Temperature).
3. Measure Resistance from Tan Sender Wire (disconnected from Gauge) to Ground.
American Temp. Senders will read: 450 Ohms (Engine Cold @ 100F)
or 29.6 Ohms (Engine Hot @ 250F )
European Temp. Senders will read: 281 Ohms (Cold @ 40C) and 22 Ohms (Hot @ 120C)
4. Disconnect Tan Wire from Sender on Engine
5. Test continuity of Tan Wire.
Zero Ohms from Block End to Gauge End - If not, repair or replace Wire.
6. Measure Resistance from Sender Terminal (on Block) to Ground on Block.
Should read as per (3) above - If not, replace Sender.
See ➥ Basic Engine Gauge Theory and Testing