Lights are dimming/pulsating. - Vintage Mustang Forums
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post #1 of 13 (permalink) Old 09-19-2019, 08:02 AM Thread Starter
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Lights are dimming/pulsating.

My interior lights (courtesy) are dimming up and down (pulsating).

They seem fine at idle but as soon as I rev up the engine a little the lights very noticeably pulsate.

I think maybe the headlights are doing it as well. It's a little hard to tell when driving.

The car runs great, starts great everything works. Not an old battery. I'm assuming the alternator is charging as the battery always has power.

Could it be the voltage regulator?

1968 Fastback, 289, 3 speed.
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post #2 of 13 (permalink) Old 09-19-2019, 08:31 AM
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Could it be the voltage regulator?

Yes.
You probably still have an original mechanical style regulator instead of a modern electronic style.
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post #3 of 13 (permalink) Old 09-19-2019, 08:58 AM
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Agreed, voltage regulator. Make sure to clean and re-seat all battery, cable and ground connections as well.

Buy a top quality Standard or Motorcraft electronic - everything else is junk. I've also heard that the NAPA Echlin unit is good.

https://www.rockauto.com/en/moreinfo...32333&jsn=3465

https://www.napaonline.com/en/p/ECHVR440
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post #4 of 13 (permalink) Old 09-19-2019, 09:20 AM
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Ditto on cleaning up and checking all the connections. It could be the regulator, itself, or the "radio noise canceling" capacitor hooked to the regulator mounting screw is bad. I have also seen this type of activity caused by a battery with a failing cell.

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post #5 of 13 (permalink) Old 09-19-2019, 09:30 AM
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For another check, use a VOM to check ALT output at idle (no loads), then, increase idle and apply a load, such as, turning on HD lights and or heater blower. These are basic ALT tests for output.
What do you consider "not an old battery"? Successful results from a reload test on the battery will rule it out.

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post #6 of 13 (permalink) Old 09-19-2019, 09:44 AM
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Mine did the same thing until I upgraded to a Standard electronic voltage regulator. One of the best upgrades I have done. Like everyone else, I removed the old tall cover from my original mechanical VR and installed it on the new one for a OEM look.

Cliff
1966 Blue Hardtop. 200 CID with 3 Speed Trans
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post #7 of 13 (permalink) Old 09-19-2019, 11:24 AM Thread Starter
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thanks guys I'll order a good quality one from Rock Auto and give it a try.

I'm not sure if mine is original. I'll have to check. For some reason I think I changed it 20 years ago with a cheap no name one from the local parts store.

1968 Fastback, 289, 3 speed.
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post #8 of 13 (permalink) Old 09-19-2019, 11:36 AM
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Ditto on checking grounds. Especially on the voltage regulator if it's electronic. Electronic needs a good ground for a reference. Check that before buying a new one.

Tom

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post #9 of 13 (permalink) Old 09-19-2019, 01:18 PM Thread Starter
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This is what I have right now. If it's not original then I may have changed it 25 years ago when I built the car.
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1968 Fastback, 289, 3 speed.
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post #10 of 13 (permalink) Old 09-19-2019, 01:29 PM
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Quote:
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This is what I have right now. If it's not original then I may have changed it 25 years ago when I built the car.
You have a modern VR already. I still think it could be bad but, as others have suggested, check your grounds.

Cliff
1966 Blue Hardtop. 200 CID with 3 Speed Trans
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post #11 of 13 (permalink) Old 09-19-2019, 01:40 PM
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I had a different brand vehicle doing that. It would also noticeably flicker the headlights a little. When looking I shortly noticed there was a ground strap from the back of the alternator to the engine and one end had broken. And it was fixed just that quickly. It even kind of surprised me that it did as the alternator (like our old Fords) was bolted to a metal bracket bolted to the engine. You'd THINK it would ground fine through all that, but...
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post #12 of 13 (permalink) Old 10-07-2019, 09:43 PM Thread Starter
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Installed a new voltage regulator tonight. Problem seems to be fixed!


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1968 Fastback, 289, 3 speed.
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post #13 of 13 (permalink) Old 10-07-2019, 10:54 PM
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Installed a new voltage regulator tonight. Problem seems to be fixed!

Thanks for posting this. Many people never respond as to what advice they tried and if it worked or not. They just leave everybody hanging.
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