alternator dance

[mercoupe50]

I have a problem with the charging system in that it has wide swings pos/neg as seen on the amp guage. 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. Could it be a grounding problem??

[flipscobra]

Check your grounding mine was doing the same thing. found out they had it grounded to the fiberglass fender instead of the frame or motor

[JBCOBRA]

Hi Mercoupe50
I was having an Alternator problem last week. Scroll threw a few pages of Club Cobra and find the thread "I need some electrical advise please". There are a lot of great ideas in there for Alternator problems.
JB

[RICK LAKE]

mercoupe50 If this is at idle, you have too much of a load on the charging system. What is the ampage of the ALT? Make sure the battery terminals are clean and tight, Make sure you have a good ground between the motor and the frame of the car. You said a 460 race motor, are you running MSD or other ignition hi output? These suck alot of amps from the charging system. If you are running under drive pulleys, the ALT is not spinning enough to charge the system. Raise Idle to 1,000 rpm is the problem gone? If yes idle or pulleys driving the Alt too slow, If not regulator is going bad. There is no 100% way to check the regulators and Alt's, except under heavy loads for long periods of time. Start with the main connections at Battery and Alt. wiggle them, make sure there is no movement then goto what's listed above with the rpm's. What other loads are on the electrical system when this happens? Lights, Coolant Fans, Heater Fans, Radio, AC system? you get the idea. Come back with what you find. Good Luck Rick L.

[mercoupe50]

The problem shows up at fast idle and at highway speeds. Sometimes truning the lights on makes it better and sometimes makes it worse. I will check all the grounding at let you know what I find. It will happen when all accessories are off.
Thanks,
David

[mercoupe50]

The cobra has been in a museum for a few years and I am back to trying to chase the problem.

I havei checked the ground wire from the battery to the frame. I have run a wire from the frame to the motor. I ran a wire from the motor to the regulator thinking the alternator might not have a good ground. The alternator and regulator have been replaced.

If the battery is low I don't get the dance while it is charging. Once the battery is charged, I get the dance, more at fast idle then slow. If I turn on the headlights on high beam the dance goes away for a period of time on fast idle. It later returns but not as bad. So with a load I don't get the dance?

All ideas are welcome.

[lvhdude]

I had a similar problem on an unrelated vehicle. Problem was the signal wire to the Voltage regulator was not seeing actual battery voltage. The solution was to run a wire directly to the regulator from the battery. It's in an RV, and I didn't want to chase the wiring all through the coach to find the source of the problem, but that solved it, after haveing the alternator (w/built in regulator) rebult once, and replaced once. Might be worth a try just as troubleshooting.

[madmaxx]

Open your trunk, pull carpet up behind battery box it will be glued down, disassemble ground connection from frame you will probably find the end connection on gnd cable from battery severed or close to it. Exact symptoms I had!

[mercoupe50]

I was back out in the garage working on the Cobra today since it is starting to get relatively warm outside.
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 pickup the frame ground although I know that there must be a place.