Topic: Pulsating interior/exterior lights when engine is running.

[priceless]

I remember sometime back reading a discussion about this problem. I can't remember which forum I read it on. I also tried the search here with no luck.

When the Mustang is started, all lights interior and exterior, pulsate from bright to dim rapidly. I'm no electrical guru but my instinct tells me its in the voltage regulator.

Any help would be appreciated.
 

[67gtasanjose]

OE style VR's pulsate on-off fairly regulary and can cause this...a battery not up to snuff might add to how frequent and how pronounced this might be.

[CharlesTurner]

Good upgrade for driving to go to an electronic voltage regulator.

[priceless]

OE style VR's pulsate on-off fairly regulary and can cause this...a battery not up to snuff might add to how frequent and how pronounced this might be.

It won't cause a fire would it? The battery is fairly new (repo Autolite) and has 14.12 volts sitting still. Should I go ahead and replace the VR?
Thanks for any info.

[69cobrajetrugae2]

My car did the same thing. With the lights off and running it was about 14 steady. With the headlights on it varied wildly between 13.8 to 14.2, which explained the flashing lights.

There is an unused bolt hole located in the back of the passenger side head. I attached a heavy duty copper strap with a tin coating from the head to the blower motor stud. The voltage is now steady with no flashing lights. Extra grounds increases the reliability of any circuit. My car must have been hunting for a ground under load.

The other possibility is that the battery has blown out one of the diodes in the alternator. The alternator will charge, but when placed under a load it begins to give up. A Battery can fail in a number of ways. Intermittent shorts between the cells is the worst. A battery in this condition may start the car, but as the battery vibrates the sulfates can partially bridge the positive and negative cell grids and hammer the diodes in the alternator.  If I remember there are 3 diodes in our alternators.  By the way, the diodes are now made offshore as far a I can tell.

My suggestion is to remove the alternator and have it bench tested at a shop. If it is good then try the ground strap.

The other possibility is a loose wire or connection. Using a volt meter with a needle, otherwise known as a D'Arsonval movement, attach it to the battery and start the car. First observe the reading with the lights off. Then turn on the headlights and high beam and very slowly and carefully disturb the connections at the voltage regulator, alternator, and ignition key plug under the dash to start. Your assistant must watch for any change in the meter movement.  If the assistant notices a change they yell STOP!  At that point you have found a problem. It may not be the problem you are looking for, but it most likely will be. If your assistant is not diligent in observing the meter, don't bother doing this test. Be very gentle on the wiring, just a little tug and wiggle, ever so slight, is all you need.

Mechanical voltage regulators can exhibit this condition. I wouldn't worry about it if that's the case. If you have a solid state regulator then try the aforementioned tests. Good luck.

[priceless]

Mechanical voltage regulators can exhibit this condition. I wouldn't worry about it if that's the case. If you have a solid state regulator then try the aforementioned tests. Good luck.

I bought the voltage regulator from a mustang vendor sometime back. How can I tell if it is a mechanical or solid state?

Would it be best to just convert to electronic? I'd like to keep the original look of the VR. Would I do this by switching the VR cover onto an electronic unit?  I've heard people doing this. But, I'm not going to put the 2 pop rivets back in place, I would just use screws.

[69cobrajetrugae2]

Here is both with a typical circuit diagram for the mechanical.  Give me the voltage drop reading across the battery with the lights on and off.

[Texas Swede]

I used to have a similar problem and found out that the reproduced voltage regulator was
built to work with original alternators but the reproduced alternators by various vendors has    about 60 amps while original alternators for 289 was 38 to 42 amps. I bought an electronic regulator and put an original cap on it. Worked fine since then on both my cars.
Texas Swede

[priceless]

Good upgrade for driving to go to an electronic voltage regulator.

So, if I go to a parts house, what voltage regulator do I ask for to get the electronic for my 69 Mach1 that will bolt into place?
I would be using my cap. I'd just drill it off then just screw it to an electonic VR.

[drummingrocks]

I remember sometime back reading a discussion about this problem. I can't remember which forum I read it on. I also tried the search here with no luck.

When the Mustang is started, all lights interior and exterior, pulsate from bright to dim rapidly. I'm no electrical guru but my instinct tells me its in the voltage regulator.

Any help would be appreciated.

Several of my cars do this; some are worse than others.  The '69 Mach and my '65 convertible aren't bad, but my '66 fastback and coupe pulsate noticeably.  I'm fairly sure the '66 coupe has had the original VR replaced with a Motorcraft replacement.  I always assumed there was a ground that wasn't making good contact, but I never had time to track it down.

[Brian Conway]

 author=priceless
So, if I go to a parts house, what voltage regulator do I ask for to get the electronic for my 69 Mach1 that will bolt into place?
I would be using my cap. I'd just drill it off then just screw it to an electonic VR.

I went to O Reilly auto and got the #2VR2 $17.00.  Brian

[69cobrajetrugae2]

The instrument panel gauges and other electrical devices ground to the forward bulkhead. When I had the dash out repairing the tach I cleaned and reattached them. There was one or two. For this reason there is a ground strap from the frame to the engine. The ground from the battery is attached to the engine block. If there is a loose rivet or spot weld in the inner support panels then the ground is interrupted. Adding extra grounds is always a smart move.

A device that is hunting for a ground can overheat and can be damaged, possibly causing a fire. 

The first thing I learned in advanced automotive is that Japanese cars have redundant grounds, unlike American cars of that era. The Japanese cars a up to a dozen grounds and American cars had 3 or 4, if I remember correctly.

This is one reason Japanese cars attained a reputation of building quality cars.

[priceless]

Thanks Brian for the PN and Thanks to all who have responded to this thread.

I'll find the root of the problem, but first, I will try the electronic VR way.

[Brian Conway]

Another picture with the cover off.  Don't forget the two screws holding the VR body to the fender wall are also the grounds.  Brian

[priceless]

Another picture with the cover off.  Don't forget the two screws holding the VR body to the fender wall are also the grounds.  Brian

Cool, thanks a bunch for the info