[VetteVet]

Well you threw me a curve with this one. I thought you were talking about a 67-72 gauge.
As you can see the bottom silver post is grounded to the cluster and you stated that you thought was Pos. Which is why I said you might get into trouble.

If you ran a positive wire into a grounded post then you'd have a short and trouble.

So what cluster do you have? the 67 to 72s were the same and the 73 to 87s were about the same. If you have an 84 cluster you can just follow the circuit board wires to the gauge to see which is positive and which is the sender for your 84 gauge.

You might be able to get a better answer on the 84 truck forums, but if you use an ohm meter. and check continuity then you can tell which post is the ground post for the gauge.

Most all the gauges use a green wire for the sender to the cluster plug and a pink wire to the power (pos) post. I looked but I didn't find a circuit diagram or temp gauge that showed the back with the correct wiring. I will keep checking because I am curious.