Nottingham15

Following on from my ongoing throttle position sensor problem on my 2000 XJ https://www.cherokeeforum.com/f2/tps-fault-198130/ my electrical gremlins are spreading.

The instrument panel voltmeter gauge is now showing 9v, "Check Gauges" is showing on the dashboard and the Jeep won't start.
But a digital voltmeter reading off the battery is 12v.

Any ideas where the voltmeter gauge gets it's reading? I can't find it on my wiring diagrams.
And does that reading prevent the Jeep from firing up, even if it's a false low reading?

I'm hoping that cleaning up all the ground connections will sort this out, but any advice is very welcome.
I really don't want to find myself searching miles of sensor wiring for the bit that's chafed off the insulation.