Patrick:
as Dennis said, "How about a bad ground under the dash?"
My first thought was that your dash lights, etc, are only earthing through your wiper motor!!
>my gauge lights started dimming..
1 All the gauges illumination shares a common earth, which loops from
instrument to instrument then
to one connection to the dash metal. It's a black wire. You might have a
dodgy contact or broken wire there somewhere.
>then the tach maxed out,
2 well, on my ser III, the (mechanical) tach is only earthed through the
same lighting earth as the rest of the guages. I'm not sure how the ser V
tach is earthed. check it !
>high beam indicator which was now flashing
3 its supplied from the footswitch hi-beam supply, but, again, its earthed
directly to the gauge
so if the gauge isn't well earthed...
>temp and fuel gauges will drop to zero...
4 these are the two instruments supplied (green&black?) via the voltage
regulator. check it (by substitution?), and check it's earthed well by its
screw to the dash metalwork.
its under the dash somewhere, don't know exactly where on a LHD ser V. it
should look like an
inch long, inch wide metal cylinder. There should be +12v on the
green&black with the ignition on.
of course, the reg won't work if it aint earthed.
>with each beat of the wiper
5 if I remember correctly, the wiper has a constant ignition-fed supply
and the *earth* is switched: the motor contact is normally earthed as the
wiper sweeps most ofthe screen and if the switch is closed, the motor is
earthed as the blades reach their parked position and off they go again.
Check the earth wire and contact on both sides of the wiper switch.
excuse any mistakes, its been a few months since I sorted my electrics, and I don't have a wiring diagram to hand.
Anyway, I'd start by checking all you earths. clean up the contacts and the metal they attach to with some sandpaper. And let us all know how you get it sorted. good luck.
Andy (Enough electrics, already. Get on with that welding, will you!)