Alternator Dance help needed
 

I have a problem with the charging system in that it has wide swings pos/neg as seen on the amp gauge. The lights go bright and dim suggesting that the voltage is actually fluctuating. The alternator belt is tight and not slipping. I have changed the alternator and the regulator and still have the problem.
The problem shows up at fast idle. Turning on the headlights and everything else to make a load makes it dance less.
It does not happen when the battery is charging when the battery is low. As soon as the battery comes up the needle dances again.
I checked the wire going from the battery to the frame. I found that ok.
There is a heavy gauge wire attached to the frame outboard of the starter that runs to the block. It is ok as well.
In the dash wire loom there is a ground wire (brown) that appears to be about 12 ga. or so. Where does that wire pick up frame ground? I really can't find anyplace where the brown wires pick up the frame ground although I know that there must be a place

Contact Blas at Windy City Cobra Club for wiring diagram specific to your serial number range--------

Open trunk, pull up carpet by battery, remove ground bolt from frame, inspect connection. You have to remove to inspect.

I did remove it and it is ok.

What is you chassis number? I know we talked before. Thought you found the problem back then...

The chassis number is 0159. No I didn't fix it but it got too cold to work on it. I do have a wiring diagram but I don't have any idea on where the earth ground connects to the frame.

Did you check the ground in the front of the car: drivers side, near the bottom (left) of radiator. Might best be seen from engine compartment and accessed from front wheel well. There are also a bunch of grounds behind the dash, near the accessory plug. Did we add the new temporary ground to the voltage regulator housing?

No I did not. I will check it. Where does it go? From to?

Had the same issue. Cleaned all the connections I could and the bounce was much reduced. Ended up replacing the ammeter with a voltmeter.

Did your voltage actually fluctuate as seen in the headlights going bright and dim? If I changed to a voltmeter I am sure I would get voltmeter dance.

Isn't the ammeter more reliable when using a generator and you have an alternator which calls for a volt meter?

I think they put amp meters in because it was original equipment. Anyone have grounding points to the frame for me?

Yes, but that was due to the alternator output dropping off at idle speed. I upgraded the alternator to a high output single wire which eliminated that issue.

I don't know a lot about charging circuits but it seems to me that If I get an alternator with a higher output, my problem will get worse since it now gets worse at higher RPM? Am I missing something?

The ground I mentioned is the front loom ground, which includes the ground wire on the voltage regulators case

Regarding a higher output alternator, while many owners have gone to 100-120AMP alternators, your cars wiring design is really not designed for that increased level of power. And the AMP meter is only rated for about 50AMPS too.

A properly performing alternator/charging systen will only 'produce' the amount of current it 'needs' to feed the electrical needs users requesting power, plus a little more to keep the battery fully charged.

FANS = ~6 - 25 AMPS
ELECTRIC FUEL PUMP = ~3 - 6 AMPS
INSTRUMENT PANEL (7 x 0.27AMPS) = ~2 AMPS
BRAKE LIGHTS = ~3 - 6 AMPS
RUNNING LIGHTS = ~3 - 10 AMPS
MSD 6 OR 7 SERIES IGNITION CONSUMES APPROXIMATELY 1 AMPS/ PER THOUSAND RPM.
LICENSE PLATE BULB (2 TOTAL) = ~0.33 AMPS
F/R TURN SIGNAL BULBS (4 TOTAL BUT ONLY 2 USED AT ONE TIME) = ~4.2 AMPS

Keep in mind that you have a very early chassis too, so your wiring is approaching 20 years old.
I don’t remember all the details of what you have done to fix the problem so far.

Are you using the same alternator that was on the car for all the years is was a museum piece? And did the car just "sit" for years or was it driven occasionally?

I assume the battery in new?

Get a short piece of brown 12ga wire, put two alligator clips on the ends, clip one end to the case of the voltage regulator and the other to the mounting bolt for the alternator, any difference in the movement of the AMP meters needle?

An AMP meter in a properly operating system will jump when headlights, turn signals or fans initially turn on, but should settle down and steadily register approximatley 1 to 1.5AMP more than the total AMP draw being used by the cars electrical system.

There is a red indicator light just above you ignition key, when does it light up on your car? Is it on when you turn the ignition key to the 1st position? Does it ever glow a little bit when the car is running?

Blas,
The car was in the museum for a few years but driven occasionally. I changed the alternator and the regulator. The red light does come on sometimes (flickers) at low idle when cold. The car was built in 1996 so it is old but not ancient. Yes the battery is new. I will check the other things this afternoon and let you know. Thanks for your help. It is really appreciated.

Red light flickering on at low RPM's is normal. Any glowing on the red light indicates a problem with one of the trio of diodes in the alternator...
Keep me posted regarding our phone conversation earlier today.....

Blas,
The red light does come on when the key is turned on but not started.

The jumper didn't make any difference in the needle movement.

The voltages are as follows:

1000 rpm 1200rpm 1400rpm
Alternator 12.65v 13.44v 15.75

Solenoid 12.23 13.09 15.25

Battery 12.29 13.22 15.48


It seems that If I increase the rpm above 1400rpm, the voltage doesn't stop climbing to over 16 volts. A bit high?

I did locate the ground on the drivers side front.

The rpm columns need to be shifted to the right.

another thing that may or may not be related but I will mention it.
When I bought the car, I found a connector mid-lower dash that contained one red wire and one brown wire about 12 ga. The connector was toasted and the red wire was burnt. The battery was bloated as if it received a heavy charge. I stripped back the red wire and put sleeve connectors on the hot and ground wire. I noticed today that the red wire gets pretty hot while the car is running. The amp meter dance was there when I bought it. I didn't notice it when I bought it however. I talked to the guy who had it on consignment at a dealer and he said that his mechanic said if it settled down it wasn't a problem. smoke smoke smoke. Periodically when driving on the road it would settle down. I haven't driven it much so it hasn't been a top priority until lately when I would like to sell it but I won't sell it with a problem.

Ah...the plot thickens......
Yes, 16 is "WAY" to high... you definately have a charging issue, perhaps just the regulator but maybe the alternator too.
High 13's is normal, maybe even 14.0 .... (I like to see 13.45)
I would start there... VR first then do voltage tests again....
You could toast the harness's and battery with your current voltage readings.

Regarding the burnt wire....
Bad, Bad, Bad.....
Can you send a photo of it to me.
Also the wiring on the alternator... send a photo
Can you determine where the damaged red wire ends go? I assume the one end you fixed is just isolated and tucked away now. but where does it originate from in the harness?
Do you have an accessory plug (lighter) installed on the car? It was an option in the early days...
It should be located between the 2 up-right supports on the tunnel close to the one on the passengers side....
Is that the area where the 2 tosted wires were/are?
Bloated battery is serious overcharging or total discharge and then freezing and expanding the case....
My email address in below.
ADD PHOTO OF BACK SIDE OF AMP METER IF POSSIBLE SHOWING WIRING

More thoughts:
I recall someone hooking up the alternator incorrectly with problems similar to this.... I think it was the ground wire...

OK... Went thru a couple hundred emails...
Similar problem solved when:
1.) Crimps on 2 AMP meter connectors were found to look ok with black isolation sleeves on them but loose when removed and recrimped.
2.) Alternator miswired - ground & stator wires switched.

Still Thinking