T25 - Temp light

[dub dub]

The temperature light is intermittently coming on. The light flashes and the needle goes up with just the ignition on, before the engine has even run.

Today I have cleaned the sensor on the expansion tank in the back, the sensor had a bit of sludge on it. I've cleaned the spade connectors on the thermostat housing, and the coolant is at the correct level.

I then started the van and let it idle, after about 10 min sat on the drive at idle the light started flashing and the needle came up so I put the dash fan on, then the needle went down and light stopped flashing.

I'm not sure what to try next, anybody have any ideas?

[marlinowner]

If the gauge is going to max even before starting then there is a problem with the temperature sender or the associated wiring. A problem with coolant level circuit will only move the gauge needle slightly.
Try disconnecting the wires to the sender on the thermostat housing. If the problem then goes away I would suspect the sender. If the problem is still there then there is a short to ground somewhere between the gauge and the sender.
If the engine is actually getting too hot after idling for a while then maybe the thermostat is stuck.

[dub dub]

Thanks for the response, much appreciated.

The fault was with the dash wiring, the copper tabs on the plastic printed circuit board.