My classic sti has got a probem... when you turn on the ignition the temp guage needle goes off the scale and then when you start the car it drops back down to lowest but then it doesnt work?? Anyone any ideas plaese

 

I expect the -ve earth connection to it is buggered(?)

 

Could be the sender, could be the earth, but there is only one wire to a classic sender.

Look under the alternator: there are TWO senders facing forwards and one facing down, (ie: two screwed in HORIZONTALLY and one VERTICALLY).

The vertical one is the oil pressure.
The other two are for water temp.

Now ONE has only one wire to it, the other has two.

You want the one with ONE wire.

First, try touching a wire from it's base to battery earth. If this doesn't help, check the wiring especially the connector on top which may be corroded/dirty.

If it needs an earth, I'd unscrew it and screw it back in with a large ring terminal under it, connected to earth, but wind some PTFE tape around it first to ensure a good seal.

If this doesn't help, you may need a new sender, but be warned, they are over £40 new