Jim, that's ihe voltage regulator for your gauges doing that. It's a common Ford deal,my 88 t-coupe does it too(scares the hell outa me).The regulator is a small rectangular unit plugged into the printed circuit on the back of the insturment cluster It;s silver and the connections kind of remind you of the terminals of a 9 volt battery.It's function is to pulse a low voltage(5volts or so I think) to the fuel,oil press. and water temp. gauges.I've changed any number of them on Fords over the years including 2 on the 88 and they still act up sooner or later for no apparent reason.They're pretty much junk in my opinion but short of aftermarket guages we're stuck with 'em.
