The temp gauge on my 85 stopped working. The rest of the gauges work fine so I think it has to be a sending unit or wire. Problem is that I don't know where it is. Please help me.

 

I just battled this, mine would read cold when the engine was fully warmed up - the sensor on the block needed to be replaced and then it worked again - resistance goes down as the sensors warms.

Before you replace it, be sure the connection is good - clean the connectors and use dialectric grease to be sure the connection is good. Also make sure there is good connection all the way through the harness if you still don't have it working good at that point.

 

The temp sender is usually a little bullet connector (although some of them are spades) near the back of the driver's side of the block. If you have a beehive cooler, it is only a few inches forward of that, and will be a p.i.t.a. to get to. I believe it's a 12mm.