Derrick Reynolds

My battery gauge started behaving like the alternator was dead. Slight discharge going down the road, bigger discharge when turn signal is on, or brake lights on. I tested voltage at the battery when idling, and got 12.0v, so I changed out the alternator.

Tested the voltage at the battery at idle today, 14.5 volts, so the new alternator sounds good. But the battery gauge is still showing a discharge when I step on the brakes or use the turn signal. Any ideas what to check?

7T1vette

How old is your battery? Checking car battery with a voltmeter is pretty useless of evaluating viability unless there is a dead cell in it.

Peterbuilt

Put a load test on the battery.

Derrick Reynolds

Battery was replaced in September of 2017.

cardo0

Wow that ammeter wiring is one of the most confusing I have ever seen. I wiring diagrams I looked up on line were for "early" 1970 so there maybe a difference with yours. But both ammeter leads connect to the horn & buzzer relay. So I have to assume the ammeter is actually a voltmeter that shows the polarity and amount of differential across those wires using the resistance in those wires to generate a voltage drop somehow but I truly can't explain it as they seem like electrically the same connection.

So for your problem I would try a new horn & buzzer relay. Next I would inspect your wiring for the ammeter to see if any has been changed from stock wiring and changing the resistance for the ammeter circuit.

Hope this can help.

Peterbuilt

You right! Both ends of the ammeter wires connect to the same horn relay terminal, but the BLACK continues on and connects at the battery terminal on the solenoid.
The gauge scenes electricity flowing to or from the battery.

https://docs.google.com/viewer?a=v&p...2ViOTE5OWQxMjA

Derrick Reynolds

I don't have a load tester here, so I pulled the battery and brought it to the local Advanced Auto Parts where they test them for free:




Battery tests as good under load.

Peterbuilt

OK, the battery is good!
It's important to have a charged battery when checking for electrical problems.

You might want to check and clean all the wire connections, like at the horn relay, alternator and at the starter.
Let's leave the back of the gauge alone for now and do the easy ones first.

NOTE:
Do this with the battery disconnected.

Derrick Reynolds

Done. All look good. There is a wire disconnected from the horn relay, but it has been that way since I bought the car. It is black with a brown stripe, and it is my understanding that it is for the key buzzer. The connector that is on it doesn't fit the place on the horn relay that it looks like it is supposed to go, so I have left it there for the last almost 10 years. All other connections in those two places look good.

Rescue Rogers

I believe yours is wired the same as my 68 was origianlly. Do you know the output of the alternator you have?. I know the stock ones were only about 63 amps. The car didnt use too much power so it had small amp output. With my original alternator my amp gauge acted just like yours. It deflected to show how much load was on the system but I didnt pay attention to the numbers as they arent really calibrated, they just show a general indication of whats going on. Mine never really went positive, it stayed near 0 and deflected towards negative under load.

If you need a more precise measurement you'll want a voltmeter. Most people here have gone to them. I like the amp meter because it was stock. I may go to a voltmeter under the dash or install one on the pillar.

This winter I added a 100amp alternator for an electric cooling fan and that really screws with my amp meter. Now it deflects slightly in the correct direction (neg) when I turn on lights and signals but very slightly since everything except the headlights is LED. But when the new engine cooling fan comes on it jumps to the positive 30 to 35 amps+. I dont think it likes high amperage loads or how its wired into my system. Atleast I know when my fan kicks on.

carriljc

Which alternator did you get(amps capacity)? Sounds like it is undersized.

My 68 also did the same thing with the stock alternator. About the only time it did not indicate in the Negative (when idling) was if I wasn't using anything but the engine and the radio. If I turned anything else on it would go negative unless I was rev'ing higher.

I upgraded from an externally regulated 10si, to a 94 amps 12si, and finally to 140 amp CS-144. (I added a bunch of loads A/C, EFI, Elect Fuel Pump, Mark-8 fan).

Take a look at your alternator and/or other info you have on it and share that.

Derrick Reynolds

The stock alternator was part number 1100884, rated at 61 amps. The replacement one is a CARQUEST unit rated at 63 amps.

Rescue Rogers

In my experience, everything seems normal then. If you want a more accurate reading, you will want to add a voltmeter

carriljc

This really sounds like the same situation I had with my old 63 amp alternator. You may have received a slightly under-performing rebuild so it's just not able to keep up. I suppose you could ask them for different rebuild...however...
(search the forum and read up on alternators and alternator conversions)

I would suggest just moving up to either a 94 amp 12si alternator OR up to a CS-144 140 amp alternator.

The 7127 should be a 10si alternator.

It's easier go to a 94 amp 12si, but I ended up at the 140 amp CS-144 anyway(if you do not plan on adding a bunch of electrical loads the 94 amp 12si should be sufficient).

Here is some alternator info, read through it and you will note that it is easy to "re-clock" the alternators and to change the pulleys (in case you need to swap a serpentine pulley for a v-belt pulley).
http://www.madelectrical.com/electri...elcoremy.shtml

You can also bounce around that website for additional useful info.

Derrick Reynolds

I talked to a guy I have known for a long time, sort of a friend of a friend, and he said he would take a look at it this morning for me. So, I get in the car, and drive over to his place, and the gauge is working just fine. The only thing I can figure is that when I disconnected the battery to change the alternator, when I put it back, I did not get a good connection. Then, when I took the battery out to be load tested, and put it back in, I did get a good connection.

Anyway, I'm back on the road! Thanks for the help!

PK

calwldlife

or the battery was charged up for the testing and that was it.

Derrick Reynolds

I keep the battery on a "maintainer" whenever I think I won't drive it for more than a few days. The battery should have been fully charged, or nearly so, for all of the driving I mentioned above.

nearflack

battery and alternator are both new. It just started doing this before I changed them out. Had be working fine previously