The Temperature Sender that uses a single yellow wire running from the gauge does not read correctly!

For the sender and gauge to operate correctly, the sender must be threaded into something that is grounded to same grounding source as the Temperature Gauge. The ground path for the sender is the sender's mounting threads. Use Teflon PASTE on the sender threads to make a good seal while maintaining a good ground connection. Do NOT use Teflon TAPE (Teflon tape will not provide a good grounding connection)!