Temperature gauge showing "right" number, but then decreases

[Oday32-CC-LA]

Happy Friday,

I just installed a new temperature gauge and sender unit.
When starting the engine the gauge doesn't seem to work or move at all.
However, when I turn the engine off and then the ignition on, the gauge moves up to a number which looks right. If the engine is then started, the gauge goes back all the way to the left (0) after a couple seconds.

Has anybody experienced something like this before? What could the issue be here? What have I done wrong?

Thank you all,
Sascha

[Dave Neptune]

Sascha, you may have the gage wired to the "start" wire to the starter and not on the "run' wire position or often times the + post on the coil. These are the "key switch" positions.

Dave Neptune

[Oday32-CC-LA]

Thanks Dave,

I will double check that.

I assume that the "start" wire has NO energy running when running the engine, correct? I am sure that the same wire I used is also connecting the electric fuel pump. Since the engine actually runs and is not turning off, I am thinking that I am using the "running" wire --> no energy on the fuel pump, no fuel, no running engine...

[Dave Neptune]

When the key is in the start position the "start" wire and the Ignition (coil) wire are both hot. When the engine starts and the key is relived to the run position the ignition is still hot and the start wire should be dead.

Dave Neptune

[sastanley]

If your boat has any colored wires back there behind the panel (which I hope it does!), the purple wire is usually the "+12v while running for gauge power" and is usually daisy chained to all the gauges.