trouble shooting an ammeter

[Robert M.]

The ammeter in my 67 coupe shows no movement no matter what is turned on or after a start. I don't thin it is working. What is the easiest way to check it? Thanks

[Ed S.]

Re: trouble shooting an ammeter

Robert,

Your question got me thinking - I may have the same problem. My ammeter indicator never moves. I just did an internet search for "troubleshooting an ammeter". Got a lot of hits, one in particular caught my attention. The URL for this word document is: www.ncrsmac.org/garage/Troubleshooting Corvette gauges.doc. This URL will take you to a word document titled "Trouble Shooting Corvette Gauges". There are no credits or author's info on the word document. If you scroll down you will find some tips on troubleshooting ammeters. I haven't read the entire document - looks like it might be useful and worth saving. It obviously is derived from an NCRS file somewhere - if anyone can shed some light on the document it would be appreciated.

By the way - I obviously cannot endorse (or criticize) the technical accuracy of the advice in the document.

[Stuart F.]

Re: trouble shooting an ammeter

The Ammeter in my 63 hardly ever showed any movement for many years until I had an alternator failure (broken pigtail led to diode failure). I replaced my alternator with a new spare that I had that was mfg. in 1969, and had a slightly higher amperage rating. I also changed out the regulator with an aftermarket piece (a Sorenson). Since then, my gauge reads out a charge after a long crank and shows a step down as the engine warms up (naturally).

Point is; it may not be entirely the fault of the gauge.

Stu Fox

[William C.]

Re: trouble shooting an ammeter

Bear in mind that an "ammeter" in a mid-year Corvette is not actually an "ammeter in the true sense in that it doesn't measure amps flowiin out of the battery (or in) but it actually is a very sensititve voltmeter that measures the voltage drop across two ends of the feed wire into the main harness. You can see this clearly if you look at the wiring print hard enough. Normally an inop ammeter is due to corrosion or loss of contact at the front of dash connection between the fuseblock and the engine compartment.

[Dennis O.]

Re: trouble shooting an ammeter

I am somewhat of an expert on this, having just gone through the exercise of tracking down the cause of the non-operational ammeter on my '67. First thing is to do is determine if it's the ammeter itself or the wiring. At first glance this looks like a daunting task. By taking out the seat and steering wheel (pretty easy), I was easily able to get my 72 year old, 240 lb, arthritic body into the car and was able to easily access the area under the dash. Use a couple of jumper wires with alligator clips on the long screws out of the back of that alternator and a "AA" battery to check the operations. If it moves, it's good, if not it must be replaced, which is a big job. If it responds, as mine did, there is a problem in the connections. Next, I used my multi-meter to check the resistance between one side of the ammeter to the main power connection on the alternator. This should be quite low, I think around .25 ohms. If it is, the next thing is to check the resistance between the other post on the ammeter and the connection on the starter solenoid. To do this, I would have had to get the car on a hoist or at least up on jack-stands. Being the lazy guy I am, I decided to see if I could get around this task. Knowing what I know about "bulkhead connectors", my next step was to turn the head lights on and then apply pressure and a slight twist to the bulkhead connector from under the hood while an assistant watched the ammeter. Sure enough, I got lucky, and when I held the bulkhead connector in the proper position, it read a discharge. As a matter of fact, it even worked properly for several seconds after I started the car. This means that the problem is in the bulkhead connector, which is not unusual. When I get back from Florida next spring, I am going to disconnect and clean the bulkhead connector. From threads I've read, this can be an easy task or a difficult one, because the components involved are quite delicate. When I get back next spring, I'll have been Corvette-deprived for 6 months and will have the ambition and desire to dive into this and fix it properly. Until then, I bought one of those $1.98 voltmeters that plug into the lighter so I know I'm charging. Life is good.

[Gary B.]

Re: trouble shooting an ammeter

I agree with waht Dennis said. But, you can also take a volt /ohm meter, set on Ohms, and read across the two terminals of the amp gage, after you disconnect the wires. If you get a Ohm reading, the gage is good. Looking at the wire schematic for a 67, one side of the gage goes out to the horn relay. The other side, a solid black wire, goes out to the large battery post of the starter solenoid. Some people, mistake this wire for a ground wire (being black with a large terminal) and they will ground it along with the other ground wire in that area, that fastens to either the bellhousing or starter bolt. That will cause a direct short of the amp gage, letting all the white smoke out of the wires and filling the gage with nice white smoke....
I just fixed a 67 roadster and that is what was causing his gage not to work.
Moral of the story, check the wiring before you replace the gage. Otherwise, you may fix the gage twice... Just set the volt ohm meter to Ohms, put one wire of the meter to a ground, and see if either amp gage wire goes directly to ground. Quick check.

Gary Bosselman