Hi.. I have what seems to be a common issue; the bouncing temperature gauge. It seems to go back down to normal operating temp with a swift smack of the dash. I thought I would try to add the extra ground behind the dash that many forum members have had success with. My question is.. what gauge of wire should I use for this ground? Thanks.

I would guess it has more to do with the connections, not the gauge of the wire itself. But I haven't worked on that car so I shouldn't speculate about the wire gauge.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra

I've just replaced by temp gauge - it was doing exactly what you have described. Plus giving inaccurate readings.

The worst problem with the gauge was it was reading hot so I needlessly replaced a lot of items which didn't need doing

Thanks for the replies. I'm going to give the extra ground wire a shot this week.