Another '67 Amp Gauge Question...

[PTighe]

A couple months ago as some of you may recall, I think I fried the amp gauge in my '67 accidently, after shorting a hot terminal on the horn relay to the frame. You guys said the windings were probably cooked on the gauge, and that sounds logical.

Now....I'm still trying to prove to myself the gauge is bad, before removing it for a rebuild. I bought a new Sunpro amp gauge for $12, just to do a couple of tests, so I can understand how this thing works.

First, I placed a continuity tester on the posts of the new amp gauge, on a bench, and the tester needle swung to the right, so I have continuity between the posts. Then I took a 12 volt DC flashlight battery and hooked up the posts on the amp guage to the + and - sides of the battery. The needle went from 0 to about 10 on the + side. When I reversed the connections, the needle swung to the - side. Easy enough.

So I decide to do the same test on the amp gauge in the car; they are both auto amp gauges and the principle of testing should be the same. I disconnect the 2 wire plug from the amp gauge under the dash and hook up some jumper wires to the continuity tester and I have continuity between the posts like the new gauge....hmmmmm. Then I do the 12 volt flashlight battery test like above and the needle doesn't move.

So taking this one step further, I took the cheap Sunpro gauge and hooked up a battery charger set on just 2 amps to the posts and the needle pegs off at 60 amps to the + side, out of control. I just did this for an instant. Why didn't it just read 2 amps, which I set the charger at? The charger is a standard 120 volt AC with a 12 volt step down which is......AC or DC? I don't know.

What I don't get is....why should I be getting continuity between the posts on the gauge if the winding is cooked? I just don't get it. Is the continuity between the posts a separate circuit from the winding?

The car starts and runs fine. The headlights, radio, heater motor all work. I know I should just forget about this whole thing, but I really want to find out the whole story on why this amp gauge doesn't work. Thanks for any more help!!!!

 

[magicv8]

Corvette electronics 101c2

You are looking at the difference between a Sunpro ammeter and a GM galvanometer that measures the voltage difference between the horn relay and the starter. The fact that they labeled it ammeter is irrelevant.

The sunpro should be connected to a car battery when you put the 2amp charger on the meter and the battery (if you want to read 2 amps).

Did you disconnect the GM "ammeter from the main dash harness before trying the continuity test? The galvanometer shunt connected to the main dash harness is a fat red wire with a lot of continuity.

When you remove the galvanometer/"ammeter" and open it up, you will see the reason it doesn't work. It will have a gap in the meter wire winding. Solder it back together, and it may work - if it isn't fused together elsewhere in the winding.

 

[JohnZ]

Expanding on Dave's post, how do the Sunpro ammeter directions say to connect it? Chances are it's a real current-measuring ammeter, but the Corvette ammeter isn't - they're two completely different instruments. Tell us how the Sunpro is supposed to be connected and it will shed some more light on the issue.

 

[PTighe]

Thanks for the info guys. The Sunpro ammeter instructions have about eight different illustrations on how to hook it up, depending on what make and year car you have, but I have learned a lot over the weekend and will eventually solve the problem. Good thing I only spent $12 on the Sunpro!!