Tail lights flickering

A few months back I posted on MC.net about my parking light problem. With the headlamps switched ON, the rear parking lights would flicker at idle. At that time, my cigar lighter voltmeter was showing a weak 10-11V. I installed a 3G alternator and figured my problems were solved…

Tonight, a fellow motorist informed me that my tail lights were flickering… I glanced over at my cigar lighter voltmeter and it was showing a healthy 13.9V.
The lights were indeed flickering when I pulled the car into the garage as the engine idled. I proceeded to switch the car OFF, restarted it, and the lights were fine. I took it around the block, pulled back into the garage, and they were still fine.

What should I be looking for here? Problem seems Intermittent. I have a Cougars Unlimited box in the trunk.


Here is a video I took when I first experienced the problem a few months back.

Joe it’s kinda hard to tell from the video, are the lights dimming or getting brighter as they flicker? I say start with the basics: bad ground? rusted taillight sockets?

Flickering, when it is voltage related, is a voltage regulator issue. Basically the voltage is toggling between the alternator output voltage mad a lower battery voltage. A properly working voltage regulator will never do this.

In the video it looks like the lights are flicker between on and off. This is a connection problem. Since the lights are all doing the same thing you need to focus on the elements of the circuit that are common across all of the lights. For example look to the common power supply lead to see if the voltage is constant. Do the lights flicker when using the brake lights?

Thanks for the replies. I figure the first step is to recreate the problem. So far I have been unable…

Nate, they flicker as if someone was cycling the lights on and off (as Bill stated). In fact, last night all of the rear lights completely shut off for a good second before turning back on.

I believe the 3G alternator is internally regulated. I also have a dummy external regulator from PA Performance which allows the dash charging light to work properly.

I will check to see if the brake lights flicker when the brakes are applied… when I recreate the problem.


It looks to me like you have a broken connection/wire somewhere. Do any lights other than the rear lights do this? May be time to trace the wiring from fuse box to rear lights with a continuity checker. Look for warn or loose connections. I believe that wire harness traverses down the lower DS of the car. You’ll likely want to pull the door sill plate and left rear interior qtr to get a good visual on the wiring.

Thanks for the replies.

Jeff, only the rear lights. I inspected and cleaned the wiring harness a couple years back. I also gave everything a new layer of electrical tape.

One thing I did not touch is the breaker mounted on the tail light panel. What are the chances of that bugger going bad?
I removed one of the wires (notice lower nut removed) and sure enough, all of the rear lights go out.

I suspect that you may have found the problem. Do you need a replacement for the breaker? I am sure I have one.

Thanks for the offer Bill. I will have to check if I have an extra in my spare parts bin.

It looks like it is a 5amp breaker… It is marked Fasco Type 4110.