Vintage Mustang Forums banner

1 - 13 of 13 Posts

·
Registered
1968 Mustang Fastback, 289, T5-5 speed
Joined
·
306 Posts
Discussion Starter #1
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?
 

·
Registered
Joined
·
10,321 Posts

·
Registered
Joined
·
37,647 Posts
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.
 

·
Premium Member
Joined
·
7,400 Posts
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.
 

·
Registered
Joined
·
502 Posts
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.
 

·
Registered
1968 Mustang Fastback, 289, T5-5 speed
Joined
·
306 Posts
Discussion Starter #7
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.
 

·
Registered
Joined
·
21,329 Posts
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.
 

·
Registered
1968 Mustang Fastback, 289, T5-5 speed
Joined
·
306 Posts
Discussion Starter #9
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.
 

Attachments

·
Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
Joined
·
21,360 Posts
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...
 

·
Registered
1968 Mustang Fastback, 289, T5-5 speed
Joined
·
306 Posts
Discussion Starter #12
Installed a new voltage regulator tonight. Problem seems to be fixed!


Sent from my iPhone using Tapatalk
 
1 - 13 of 13 Posts
Top