Dicecal

I'm thinking there is somthing wrong here: With no electrical stuff on I always have slight negative discharge on the ammeter (battery Gauge). With the headlights, radio, heater and coupe rear ventalation fan on the ammeter reads -20 volts in idle..does not get much better while driving. I've checked the alternator, voltage regulator, and the battery; they all check out good. Whats up here? Any ideas? 65 327-350 Base Coupe with no power accesories, 37A alternator.

62Jeff

Assuming the gauge is OK...

Sounds like one of the 2 wires going to the back of the ammeter isn't carrying much voltage. The meter measures the difference in voltage between the 2 wires. Chances are a broken or bad connection somewhere in the circuit of one of those 2 wires.

richbopp

Check where the ampmeter wires go through the firewall. These connections can become a little less than pristine and cause all kinds of ampmeter readings. Here's a quote from JohnZ, and with his permission:

"Chances are better than 9 out of 10 that you have a disconnect or corrosion between the terminals in the mating multiple connectors on the engine compartment side of the fuse block; both of the battery gauge sense wires (12-ga. black and 18-ga. black/white) go through the connector closest to the engine. Carefully remove that connector (don't break the lock tabs) and clean all the terminals."

he's the man, so look here first......

Dicecal

Thanks guys, I'll take a look at the wiring/terminals.

bweaver999

Interesting, mine is pretty much the opposite. At idle with nothing on, it's at 0. Brake lights take it to -10 or so. At 3000RPM with nothing on, it's usually at +20. It's a 67, not sure what alternator. Should it read near 0 when running down the highway or is +20 normal?

What about idle?

Seems this might be normal as it measures the difference and the battery should be 12-12.5 volts and the alternator runs at 14.5 volts at speed. Or is the battery gauge calibrated to read 0 with the difference?

The alternator has been re-built, the regulator replaced. I suspect I may have a weak cell in the battery, if I let it set for 2 or more weeks it needs charged to start. Since I got the battery tender, it seems to charge for a day or so before it goes to no charge (red to green light).

Dicecal

I'd be interested to know what "normal" battery gauge readings should be as well...

magicv8

The battery meter is a galvenometer, a simple coil of wire with a needle pivot assembly in it.

At one end of the meter coil a wire runs to the starter solenoid. At the other end, a wire runs to the red harness line connected at the horn relay (roughly reading the alternator output to the red wire splice).

The wires to the meter are always live. When the alternator is off, both wires should have the same (battery) voltage, and the meter should read zero. When the alternator runs, the battery meter should twist clockwise indicating current flowing through the harness to the starter solenoid battery connection. Most of the current goes though the harness (fat red) wires. Less than 1 amp goes through the battery meter. If the fat red wire burns, all the current goes though the battery meter and it dies - a good reason to have a 1 or 2 amp fuse at the meter connections.

Dirty battery meter connections at the bulkhead, horn relay, solenoid, battery, or alternator will effect the meter operation - as will modifications to the factory wiring harnesses.

What the meter tells you is arbitrary, depending on the condition of the harnesses, the load, and the size of the alternator. That's why I replaced my battery meter with a voltmeter.

JohnZ

After cranking to start, it will show a +10-20 charge rate for a minute or so (or less), then drop back to just slightly positive as you're driving. If it shows a consistently high charge rate, the battery may be weak or have a dead (or dying) cell.

Dicecal

Thanks John. Everything I have checked, has checked out good. At this point I believe I may have a bad ammeter gauge. While trying to take the negative battery cable off (to change the points), I accidently touched the positive battery post with the wrench while it was on the negative battery post as well. Quite a spark, now I think this action may have fried my battery gauge. You think that would fry the gauge?

richbopp

Ooooooooh Yeahhhhh. That could fry it for sure.

Have you tried an external ampmeter connected to the +/- of the connector that goes to the amp guage in the cluste and see what you get?

Dicecal

Yes, thats next..had trouble pulling the connector off. I'll grab it with some pliers and give it a good pull. Anyone know where I can get my battery gauge rebuilt?...lol

blubu

VetteInstruments@aol.com aka Jason

toddalin

Too bad it's not a '63-'64. Those gauges are a cinch to rebuild yourself using (if I recall correctly) about two dozen turns of magnetic wire. (Just count the number of turns on removal). It may have gotten tougher when the gauges went flat.

You can test the gauge in-place. Just remove the plug, put two alligator clips on the gauge pins, and touch them to a 1.5 volt battery. That is enough to make the gauge deflect in either direction if it is working.

wombvette

Carefull John, Some around here dont believe you can tell the condition of a battery by the ammeter. You are on thin Ice.

Dicecal

Thanks, I'll try that too!

bweaver999

Thanks John!!!!! Nice to know what it should read normally. Figured I had a weak cell in the battery.

Curious, is it calibrated to 0 on the difference in voltages? Seems if the alt is putting out 14.5 and the battery is at 12.5, it should always read on the plus side.

wombvette

Thats exactly what it does. It reads a small voltage difference between two points in the circuit. The reading is an indication of how much current is flowing to and from the battery. So if the alternator is supplying enough voltage to make a positive reading, you know that at least to things are happening. There is enough voltage and enough current supply to power the system and keep the battery up. The correct steady state reading is just slightly positive. If the charging system gets weak or fails, you see a negative indication. If things are good you should get a positive indication according to the demand. As John so dangerously indicated, you may be able to tell the health of some of the components of the system, if you know what to look for. When you have a new battery and a good charging system, you will see a rather long and deep charge when the car is first started. Over time this cycle will become short and shallow. This is an indication that the battery is ageing. You can see the instant demand of certain components and see the regulator take care of the that demand and then settle down. If you see odd indications such as short dips in the reading as you drive, it indicates something is happening in the system. I even look for my turn signal and brake light signal by watching the meter.

magicv8

No - the voltage regulator cuts the alternator voltage back when the battery is charged. A battery meter with good clean connections will then be centered. If the regulator didn't do that, the alt would fry the battery.

Dicecal

Well folks, I've checked just about everything and still the same result. I bought a new battery, the alternator and voltage regulator both checked good. While the battery meter could use some calibration, it delfected the same amount right and left when running a 9 volt battery thru it in both directions. So wth the headlights and blower motor on, the battery gauge deflects to -20 and pretty much stays there and does not get much better with engine rpm. With no electrical load, the battery gauge pretty much reads zero. I'm out of ideas......

62Jeff

Sounds like a bad wire.

Have you measured the voltage coming out of both wires that go the amp gauge? One of those wires may have a bad connection and not working well under a load.

Then again, I may be talking out of my rear. Less than a year ago MagicV8 had to carefully explain to me why my own gauge was going wonky.