Griff2002

My ammeter has always been at around -10 (to left about halfway to the first mark) with the headlights on. It's been like that since I've owned it - maybe even a little worse before I replaced the alternator. With headlights off the needle is vertical, or a bit to the right (i.e. charging) if I haven't driven it for a while. It hasn't caused me any problems, but I don't drive much at night. Parasitic drain is minimal.

Is this normal. If not, where / how should I look for a problem?

Thanks

theandies

Mine runs just a tick to the right of center with the headlights on, almost unnoticeable. '71

Alan 71

Hi G,
What does the gauge read with the engine off, but the headlights on?
Even further to the left?
Regards,
Alan

Griff2002

Alan,

I just did some checks and an interesting thing happened.
Engine off
Parking lights on and adjust rheostadt dim to max. -0 to -5 amps
Headlights on -10 amps
Brights on -20 amps

Engine on
Next I started the engine to double check the ammeter. Interestingly the meter stayed positive when I gave it a little gas. That is different than what I see when driving (typically needle to left). I'll check to see if the belt could be slipping but I don't think that's the issue. Going to need to do some more experimenting on this to understand under what conditions the draw occurs.
p.s. it did this with my old alternator and with a replacement I put in a few months ago.


Thanks

7T1vette

Somewhere between 5 and 10 amps discharge for headlamps. The ammeter is not meant to give "accurate" readings. It is intended to allow you to interpret the fluctuations from normal reading when running (which should be "0"). If the gauge shows 5+ amps discharge with engine OFF and lights ON, it's working as it should.

Alan 71

Hi Griff,
I'll be interested in hearing what you learn from your experimenting.
If you haven't yet, take a look at the description of ammeter's function, and how to interpret it's indications, in the Owner's Manual.
It's interesting!
Regards,
Alan

Griff2002

Thanks Alan. I read the manual and the ammeter charging system appear to be working as they are supposed to. I was concerned the discharge with the lights on was too much, but according to 7T1 it is in the normal range. Still curious why there was no discharge when I tested late yesterday - I'll keep checking and let you know if I figure anything out.

theandies

Here is my '71 with the headlights on and high beams on.

BLUE1972

The meter is not a "true" in line reading of the amperage.

I had some strange readings on my 71, when I first got it home. Used a meter found it was charging. Started to check some of the connections and found a few not so clean terminals. Problem solved.

lionelhutz

It should always read positive or charging. The amount depends on the battery charge.

7T1vette

Well, the word "should" is the operative word in the prior post. There are many cases where the ammeter shows discharge....even when running. These instances generally indicate some 'problem' with the electrical/charging system:

1. car idling with lots of electrical 'stuff' ON; alternator can't provide adequate charge at idle

2. alternator has at least one failed diode or other significant problem

3. wiring connected to [or with] ammeter system has a problem

So, the ammeter is useful to show that system is charging properly...OR NOT! And, when it is NOT, that's exactly when you NEED the ammeter.

And, most of the time, the ammeter should be running near the ZERO mark. When the system has fully recharged the battery following an engine start, there will be a slight charge present; but the amount will be so little that it hardly shows on the gauge. Getting that indication (most of the time) is what you want to see; and that's another reason to have the ammeter.

theandies

Good explanation and as indicated in the picture I posted.

Griff2002

Well the ammeter seems to show that the charging system is working ok most of the time, but that something is intermittently wrong when I turn the headlights on since I sometimes show a large discharge when I turn them on. I'm not sure where to look for the issue though.

7T1vette

If that is with the engine running, then I suspect that the power line for the headlamps is being shorted to ground somewhere. Since it does not show up when they are OFF, the problem is in the line[s] somewhere AFTER the switch. You could use an ohmmeter to find a power line which is partially shorted (battery disconnected, of course); or you can just visually inspect those power lines after leaving the switch.

P.S. It is also possible that your alternator is not putting out much charge when running. That could be a problem with the alternator, or it could be a problem with its wiring.

Griff2002

Thanks for your help. It's interesting that I tried again last night and did not experience the problem. Perhaps fiddling with the light switch eliminated the issue. I'll have to go for a longer drive and see if it reoccurs.

I've seen the issue with both my old and new alternators, so I don't think that is it (unless it's a loose or shorted wire). I think I may also want to check the bright light switch for a possible intermittent short.

I assume your suggestion for testing the power line is to check the resistance from the power line to ground (should be infinite unless there is a short)?

BLUE1972

Take a battery reading with the car off - then start the car with the lights on should be 13 to 14.8 with the engine running. Check the amp meter. If not check the output of the Alt to see if it's charging.

Drive the car and check the voltage when the meter starts to show discharge. If the voltage at the battery dropped, check at the back of the Alt. to make sure it's still putting out - if it is still putting out then there is a wire problem.
The ALT senses to charge from the horn relay. So I would make sure that post is very clean. There is a very slight possibility that the alt. is seeing the alt output but not the draw on the other wires on the relay.

I just helped a friend with headlights that would "flash" after 1/2 hour of driving.
The new IMPORTED HEADLIGHT SWITCH OF THE FINEST CHINEESE QUALITY was overheating and opening the contacts / cooling and then closing.

Rather than taking the dash apart I put relays in so the switch only sees low amperage draw. (one for high and one for low with a feed directly from the battery)

Griff2002

I've done some more experimenting and learned a few more things.

1) drove with headlights on. Initially, the ammeter was just right of zero indicating normal slight charging. However a few minutes later the ammeter gradually shifted to a slight discharge. It seemed like the alternator was charging, because the meter would move when I would go off idle.

2) today I drove without the headlights on. Everything seemed normal, with a slight charge (needle just right of zero). I turned on the lights and the meter stayed slightly right. However again, after some time the meter moved slightly to the left. Turned the lights off and everything was normal.

So it seems like something is causing a slight discharge after the headlights have been on for a while. Wonder what might cause that?

Have not had time, but next step is to follow your suggestions to inspect wiring, and check voltages (will do when cold and hot to see if there is a difference).

Griff2002

I've finally had time to check some more things to diagnose my problem. As a reminder, the issue is that the ammeter usually shows a significant discharge with the lights on and the engine running (on rare occasion the meter shows a positive charge).

Recap:
Engine Off Current Draw per Ammeter (cumulative)
Parking & Instrument lights ~ 6-7Amp; less if dimmed
Low Beam Headlamps ~ 13-14 Amp
High Beam ~ 20 Amp (sometimes more like 40 but if I click bright switch on and off it goes back to 20)
Alternator is fairly new (less than 500 miles). My old one died, and I was seeing the same issue with the old alternator.
Wiring seems relatively stock. Appears a couple of new lines were run for the electric fuel pump relay and horn relay to starter. Other than that wiring is unmolested.

Yesterday I drove ~ 5 miles with parking lights on. Ammeter stayed on discharge. Voltage at alternator when I got home:
Engine running / Lights off - 14.5 V
Engine running / Lights on - 14.3 V
Engine off / Lights off (i.e. battery voltage) - 13.6 V
Note that alternator seemed very hot.

Today I disconnected the battery, removed the taillight lenses, and checked resistance across the light socket contacts (i.e. powered contact to ground). My meter leads have about 0.6 ohms resistance so the readings below are probably high by that amount.

Left taillight contact 1 to ground contact - 1.9 ohms; contact 2 - 1.3 ohms
Left backup lamp 4.7 ohms
Right backup lamp 1.8 ohms
Right taillight contact 1 - 1.8 ohms; contact 2 - 1.8 ohms

Turning on headlight switch does not seem to make a significant difference in the resistance (remember battery is not connected).

I was expecting infinite resistance between these contacts. Do these results indicate a short, or am I doing something wrong? All the headlights, gauges, etc. are working. Only issue is the apparent discharge with the lights on - even putting the brakes on moves it to discharge side.

Would appreciate any further insight on the problem and / or how I should proceed. My plan is to check the resistance on the headlight terminals to see if the same issue is there.

Thank you.

Griff2002

I checked the resistance between the ground and hot leads of the front headlight connectors, as well as one of the front parking lights. As with the taillights, there was only about 1-2 ohms resistance. Again it seems like there should be infinite resistance between these points. Does this mean there is a short? Could this explain why my ammeter usually shows discharge with the headlights on? If there is a short, any suggestions on how to track down where it occurs? Seems like a daunting task as it could be anywhere. Again, all the lights work fine, but I fear I will either destroy the alternator or run the battery down if I run with the lights on for an extended time.

Thanks

lionelhutz

The extra wires have probably re-routed the current path. The path is now likely to the starter solenoid on a new wire and then back to the dash on the original wires. This would make the ammeter show the current being drawn by the original electrical system instead of just the current flow to/from the battery.

Your testing showed the alternator is keeping up ok. I would not worry about your meter tests. An actual short would blow fuses or burn the fuseable links or cause the headlights to flicker by tripping the headlight breaker.