Join Date: Mar 2002
Location: Austin, TX, USA
Re: 69 Console temp gauge
You say you checked continuity on the green wire. How did you do that? Did you take a resistance measurement? If so, what was your reading. The reason I ask is that a bad connection will flow current - just not very much current. Bad connections are particulary frustrating because with small loads, they appear just fine, but when the load increases the voltage disappears.
Let's also be sure you have a gauge sender and not a temperature switch used for an idiot light. You should be able to measure the resitance of the sender when cold and see it change considerably as the engine warms up.
Assuming your ohm test of the green wire is good, and that you replaced both the sender and the gauge leaves me to think one of two things is at fault. Either you're not getting power to the gauge or the ground between the gauge, battery, and block is bad.
Use a volt meter to measure from a known good power source to the power terminal on the gauge while the electrical system is powered up. You should see less than a few hundreths of a volt drop in the circuit and also be able to measure full system voltage to ground. Next measure from the block to the gauge ground. Again you should see less than a few hundredths of a volt with the circuit powered up. Keep in mind that the battery (-) pathway to the gauge is important for powering the meter, while the ground path between the block and the gauge is used for the sender return power. It's been reported that too much teflon tape on the sender can insulate it electrically from the block. Measuring the voltage drop between the sender body and the block would reveal the problem - expect less than a few hundreths of a volt drop if all is well there.
One of these tests should point to an open circuit somewhere I suspect.
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI