[TR] TR4A - Ammeter Issue

[Randall]

> with the shunt option that AAW 
> recommends for keeping the original gauge.

That's interesting, I didn't know they copied my idea <G>  What do they
suggest for the shunt?

> How does one test an Ammeter outside the car?

Basically, run some current through it and see if the needle moves.  In your
case, I would probably disconnect the shunt instead, and then verify that
the headlights won't work with the ammeter disconnected.  Then if they do
work with it connected, and the needle still doesn't move, the ammeter is
bad.  Ordinary headlights will draw roughly 10 amps (15 if all the tail &
marker lights are working).

On the bench, you'll need a source of 12v (a typical battery charger will
do) and something to use for a load.  I keep some old headlight bulbs around
for this kind of testing.  (The low beam filament almost always burns out
first, leaving the high beam filament usable for testing.)  One bulb should
draw around 5 amps, or you can parallel two of them for 10 amps.  Some cheap
alligator clip leads from Radio Shack or Harbor Freight will make the
connections easier.

-- Randall