Just pulled a 70 satellite convertible out of a very long term storage. The car hasn’t really been driven since the mid 70’s except for a spin around the block here and there. The lights flicker when the car is running but are fine when it’s not running. When running, the ammeter shows a normal charge, but will go to a quick slight discharge and back to a charge. The flickering seams to be periodic occurring every second or two.

Any suggestions on where to start?

Maybe check the ground on the regulator ??? Also, is your battery ok ??

What lights? When you say flicker is that dim to bright, or dim to out? Do all accessories do this including radio as example? Could be harness connections, Voltage Regulator, Alternator, bulkhead connection. What you have stated so far leads me to think charging system is flickering for some reason changing voltage.

"When running" indicates the alternator and/or regulator are involved in the flickering, and I'd lean towards the regulator.
Should be easy to check with a multi-meter.
Good time to check, clean & tighten ground connections, bulkhead connectors, and power cables.

Could be most anything with that description. Wiring harness, grounds, charging system, etc. Spend a little time cleaning connections and then check things with a voltmeter and you'll find it.

I had a buddy who had a Mustang with flickering lights. He had his alternator tested and replaced. He replaced the voltage regulator, charged the battery, replaced battery cables, replaced the headlight switch, etc. Finally replaced the headlight wiring harness and that solved the problems. Evidently the factory wiring harness had broken just enough wire strands that the lights flickered when he drove. Just about drove him batty looking for that flicker.

Put a full charge on the battery and see if the lights still flicker.

As noted put a full charge on battery first. If flickering still present, check diodes in alternator. Diode failure can introduce alternating current into the direct current electrical system, creating all sorts of havoc.

regulator if it is an electromechanical reg & if not then the alt as mentioned

Or it just could be normal.


Lets begin here.
When the engine is not running, power for the lights comes from the battery. The battery has a pretty big reserve of power. If the battery goes to 12.5 Volts when the lights are turned on, its going to stay around 12.5 volts for quite some time. So as long as all the connections from the battery to the lamps are good, everything is going to stay pretty steady. Of course eventually the battery will lose enough power that you will notice the lights dim.



The voltage regulator will attempt to keep system voltage around 14 Volts. At 14 Volts, the lights will draw more current than at 12.5 Volts and they will burn brighter. Some headlights are more sensitive to this than others, but all lights do it.

But at slow idle, the alternator can't produce a lot of power. It should be enough to run the ignition and a little more. Turning on the headlights and stepping on the brake pedal can sometimes max out an alternator's power at 650 or 700 rpm. If in addition to that, the battery is still recharging, and the alternator is already maxed out, system voltage will drop. Then the battery takes over for a little bit and you see it ammeter showing battery discharge, then charge, then discharge. So that's one common scenario and was pretty normal.



Same as the others. Make sure the battery is fully charged using a charger.

Then after starting, let the battery recharge. When the ammeter indicates the battery is nearly recharged (or at least less than 5 amps charging), then try the headlights while holding the engine speed up around 1000 - 1200 rpm. If it still flickers and the ammeter still drops back to discharge, then the alternator is not producing nearly what it should.
First check the belt tension.
Then if that's not is, check for a bad diode or open winding in either the rotor or the stator.

I disagree with your analysis that the alternator can't keep up with lights and ignition at idle. My 70 37amp after sitting a month or more, will start, and have no issues recharging battery, running ignition, and lights without flickering. There is plenty or magnetic field generated. Remember the pulley ratio. Current drawn from the alternator is based on the load, and it was sized to handle basics at idle. Flickering is not normal in my opinion.

Well its bordeline at slow idle - with brake lights lit. And we don't know how low the battery is. That's the point and why I don't want to condem equipment when not knowing the full picture.

As far as your not experiencing that, I beleive you.
Perhaps its because your car still has the correct equipment on it (not randomly rebuilt replacments) Or perhaps it because I drove a lot of /6 a-bodies. Only the /6 cars (maybe only the slant 6 a-bodies) got the lowest rated alternators as standard equipment. But I used to see this a lot when stopped at a light at night, especially with the wipers or heater on. I don't recall that in our '69 B with 318 and a/c - but it's been a long time and didn't drive it that much in bad weather. We replaced the starter on it, but as far as I can recall, alternator lasted its entire life.