[Roadsters] Instrument regulator test

[John F Sandhoff]

On Sat, 18 Oct 2008, Gary Boone wrote:
> ...I've pulled the regulator out and want to test it before just
> finding a new one...  How does one bench test this regulator?

Connect a voltmeter - or a small (like a dash light) 12 volt bulb
to the case and to one of the connectors. Then connect 12 volts
(polarity does not matter) to the case and the other terminal.
You should see voltage (or the lamp will light) for a few seconds,
then it will go out. A few seconds later, the voltage MAY come
back on.

For these results to be accurate, you must have the voltage
indicator connected BEFORE you apply the voltage.

If you NEVER see voltage: The regulator is open (i.e. no good).
You MAY be able to open it and clean the contacts, but it probably
won't last.

If the voltage PULSATES (on... off... on... off...) the regulator
is GOOD, and you have it wired correctly (the terminal you applied
voltage to connects to the 'hot' lead from the ignition switch).

If you get voltage ONCE and then it stays off, you have the regulater
connected backwards. Disconnect power, Move the indicator to the other
connector, apply voltage to the now-available connector and you should
see on... off... on... off...

Important troubleshooting tip: If your gauges momentarily start
to move when you turn on the key and then drop back to zero, and
you've been mucking with the wiring, you probably connected the
regulator in backwards.

If your gauges read way too high, possibly off the scale, the
regulator is either bad... OR the ground is bad. Unscrew it, clean
the screw, case, and body contact point (small wire brush) and
reattach.

"next lesson will be on how this simple box acts as a temperature
compensator so the temperature-sensitive electric gauges are
(relatively) accurate regardless of it being zero degrees or a
hundred degrees" (or check the archives :-) ). In other words,
you can't just replace it with a constant-voltage regulator.

-- John
     John F Sandhoff sandhoff at csus.edu  Sacramento, CA