Topic: '67 Amp Gauge -- Overcharging

[drummingrocks]

I've been driving my '67 coupe daily over the past few weeks, and it's recently developed a new problem (in addition to all the problems it already had).  Over the last week or so, the amp gauge needle has stopped staying in the middle of the gauge and has started staying on the above normal "charge" side.  It's very noticeable when the car is first started, and then it slowly eases back down into the normal/middle area as the car warms up.  However, more recently, it's stopped even doing that and the needle almost always stays on the overcharging side of the gauge.

I suspected either the voltage regulator (clearly not the original, but a parts store replacement) or the alternator.  I pulled a known good VR off of my '65 convertible, but there was no change.  I put a mechanical gauge on the battery, and it was receiving around 14 volts.  Every now and then, it would charge above 14 volts, but not excessively.  Finally, I swapped a known good alternator off of another car, and still, no change.

At this point, am I correct in thinking it has to be in the gauge or wiring?  I really don't think the charging system is charging as hard as the gauge indicates, otherwise the battery would boil over.  I thought maybe the instrument voltage regulator on the back of the dash had gone out, but if it had, wouldn't it make all of the gauges read incorrectly?  The fuel and temp gauges are reading fine and don't fluctuate while the car's running.

Any ideas, or suggestions on where to go from here?  Prior to this problem developing, the amp gauge needle always stayed perfectly in the middle.

[midlife]

OK...here goes.  I believe it is a wire---specifically a molded connector, likely at the starter solenoid.  While the car is running and someone looking at the gauge, examine where the main harness wire attaches to the starter solenoid.  Tug the wire relative to the molded connector and see if the ammeter goes back to normal.  Another location is where the ammeter line attaches to the headlight or alternator harnesses.  The ammeter lines are solid yellow and solid red. 

What's happening is that the resistance at the main power line has increased, allowing more of the current to flow down the ammeter side of things.  The ammeter system is responsive to fractions of an ohm difference between the main power feed to starter solenoid resistance and a similar pick-up point closer to the ignition switch.  As I said, a fraction of an ohm can cause the ammeter to go wonky.

[drummingrocks]

Thanks, Randy, I was hoping you would see this thread.  I'll test it out and let you know what I find.

[drummingrocks]

Randy, I tried the test you described, and the gauge reading didn't change at all.  It does seem like the gauge is reading progressively higher.  Whereas it used to creep back into the middle/normal range as the car warmed up, it's now pretty much staying maxed out on the gauge.  The needle fluctuates a little when going from idle to say 1500 rpm, but aside from that, it never moves from the extreme right of the gauge.

Any other ideas on what I can try?

[67gtasanjose]

Any other ideas on what I can try?

A tach dash with an alternator light!

I don't recall any of those guages ever working correctly! Randy's answer seemed to make the most sense so maybe there is another issue within the harness. Has anything electrical been changed around since last it worked normal?

Richard

[drummingrocks]

A tach dash with an alternator light!

I don't recall any of those guages ever working correctly! Randy's answer seemed to make the most sense so maybe there is another issue within the harness. Has anything electrical been changed around since last it worked normal?

Believe me, if I had the cash to spend on it, I'd love to do a tach conversion on this car.  It's gonna be a LONG time before I have $799 to spend on something that doesn't make the car run or look better! 

Nothing had changed when this problem first started.  I drive the car fairly regularly, sometimes even daily, and it just started doing this one day when I cranked it up leaving work.  I used a manual gauge on the battery back then, and it wasn't charging much above 14 volts max.  I next swapped in a known good voltage regulator--no change.  I swapped in a known good alternator--no change.  Other than parts swapping, nothing has changed, and none of what I've done so far has affected the gauge reading.

[67gtasanjose]

Maybe you can do a voltage test at different areas around the car (Key on, engine off and again testing the same places, key on, engine running)...like at the ignition switch accessory post, alternator main post (output), fuse panel etc. You should be getting about the same voltage on your meter at all the locations, battery voltage with engine off and obviously around 14-14.5 with engine running, but all within say 1/2 a volt of one another. This might narrow down the problem some.

Richard

[midlife]

OK...sounds like one of the ammeter wires or their connectors are bad.  The main connector from the headlight harness to the underdash harness is a two pin yellow molded plug.  First disconnect the battery, and then disconnect the plugs.  Inspect them, tug on the wires back from the molded plug, and reconnect.  Then connect battery and test.  If still the same phenomena, disconnect battery and do the same on the 12 pin plug between the underdash and the dash cluster.  Check to see if that helps.  If still the same, check for the 90* connectors on the back of the dash cluster going to the ammeter.  With the battery disconnected, measure the resistance between the yellow and the red 90* connectors: it should be 0.5 ohms or less.  If so, and the problem is still there, my suspicion would then go to the main power line near the starter solenoid and the connectors to/from the alternator.  I believe in 1967, the red ammeter line has a ring connector that bolts directly to the starter solenoid.  Clean all of the starter solenoid rings well and try again.

If still the same, time to send it in to me.  I can convert to tach for $295 both the dash cluster and main harness, but you have to buy the tach-headlight harness as repro.

[drummingrocks]

Thanks for the suggestions, guys. I'll try to get it tested this weekend and will report back with what I find.  Randy, I had no idea the tach-equipped cars used a different headlight harness.  Now I'm beginning to see why the various tach conversions for these cars have always cost so much!

[drummingrocks]

Not to get off topic, but one more question about tach cars: Did the tachometer option also include the speedometer with trip function?  Or was the trip speedo still a separate option?

[67gta289]

Those were grouped together.

[67gtasanjose]

Thanks for the suggestions, guys. I'll try to get it tested this weekend and will report back with what I find.  Randy, I had no idea the tach-equipped cars used a different headlight harness.  Now I'm beginning to see why the various tach conversions for these cars have always cost so much!

Yes, all wiring under the hood (except the hood harness, if you have that option) is different, even the engine feed wiring, alternator, with or without fog lamps as well as the under dash wiring (that as Randy said, he can convert them) The other harnesses cannot really be converted very easily nor are they ever in good enough condition to consider that most of the time. About the only option that doesn't descrimiinate under the hood is the hood lamp wiring connector. It is there on all headlamp harnesses, irregardless of other options.

Richard

[midlife]

Yes, all wiring under the hood (except the hood harness, if you have that option) is different, even the engine feed wiring, alternator, with or without fog lamps as well as the under dash wiring (that as Randy said, he can convert them) The other harnesses cannot really be converted very easily nor are they ever in good enough condition to consider that most of the time. About the only option that doesn't descrimiinate under the hood is the hood lamp wiring connector. It is there on all headlamp harnesses, irregardless of other options.

Richard

The engine gauge feed harness (oil, temperature, coil) is the same for tach and non-tach, but differs between engine sizes.  The oil pressure sending unit must also change from gauge (non-tach) to indicator light (tach dash).