Pulsating/Strobing Lights Problem

iaragon

Registered User
Hello All,

I've found a few posts regarding this problem but have not found anyone mentioning a fix for it. I have a 91SC that recently (at least I just noticed it) began to suffer from an odd electrical problem. Both exterior and interior lights are strobing when the motor is running. My mechanic said it had to be the built-in voltage regulator in the alternator has gone bad (I've read this mentioned in this forum as well) but I replaced the alternator and starter relay at the same time. I did the relay because I hadn't replaced it, and it wasn't too expensive. Anyway, the strobing/pulsating is still there. I've checked all the grounds I can get to including the one on the motor mount and all seems secure. Now, I did replace my battery about 4 months ago, but like I said, I just noticed this strobing in the last 3 weeks.

Could the battery cause this type of problem? I can easily have the battery tested and it is still under warranty but I was just curious if this might be it?
Thanks.
 
You need to have someone check the ouput of the alternator. Something is either intermittantly putting excess load on the alternator, or your alternator is intermittantly outputing variable power levels.

Measure battery voltage and record figure. With engine operating off idle and all secondary electrical systems turned off, regulated voltage should be no greater than 2.5 volts above recorded figure. Turn on headlights and set heater blower to high. Regulated voltage of idle should be no less than 0.5 volts above recorded figure.
 
HI Mike,

Thanks for the input. I measured the items you described and all fell within those tolerances. Nothing new has been added to the car as far as electrical components.

Any help would be appreciated.
 
Try this..

I had a similiar problem with my '94sc. They didnt strobe bad, just dimmed a little and brightened. Upon checking the engine compartment we found a ground strap off between the motor and chassis. Once we fixed it the problem was gone...hope this helps...Jeff
 
Hi Jeff,
Thanks for the tip. Can you tell me where in the engine compartment? Driver side, passenger side, by suspension, etc...

Thanks.
 
Hi Jeff,
Thanks for the tip. Can you tell me where in the engine compartment? Driver side, passenger side, by suspension, etc...

Thanks.
 
There are two main ground straps in the engine compartment. One goes from the passenger motor mount forward bracket, to the frame, and the other goes from the drivers motor mount forward bracket to the frame.
 
On a 94 SC

On my 94SC it is located on the passenger side, on the frame directly down from the compressor. But something tells me on my 90 it was in a different place. If not on frame look on firewall, just in case your not sure what the ground cable looks like. It could be one of two choices..first being a flat cable with eyelets on each end or the braided cable with eyelets. hope that helps...Jeff
 
i have this same problem

i have been experiencing this problem for a while now...ever since i installed my 148db stereo. but i tracked it down to a 140amp draw of my amp. hehhe. just addin a little bit of humor here...or trying. later. steve.
 
iaragon said:
Hello All,

I've found a few posts regarding this problem but have not found anyone mentioning a fix for it. I have a 91SC that recently (at least I just noticed it) began to suffer from an odd electrical problem. Both exterior and interior lights are strobing when the motor is running. My mechanic said it had to be the built-in voltage regulator in the alternator has gone bad (I've read this mentioned in this forum as well) but I replaced the alternator and starter relay at the same time. I did the relay because I hadn't replaced it, and it wasn't too expensive. Anyway, the strobing/pulsating is still there. I've checked all the grounds I can get to including the one on the motor mount and all seems secure. Now, I did replace my battery about 4 months ago, but like I said, I just noticed this strobing in the last 3 weeks.

Could the battery cause this type of problem? I can easily have the battery tested and it is still under warranty but I was just curious if this might be it?
Thanks.

When your lights (both interior and exterior) go off, do they flash on and off fast making a clicking sound?

If so, it's most likely your headlight switch. They are known to go out on these cars when you use the fog's. A replacement for the switch is around $40 without autolamps and $50 with....pretty easy to replace it as well.
 
No, I've dealt and fixed that problem. And yes, that turned out to be the headlight switch that many others of have had problems with too.

This problem is not related, there is a subtle strobe/pulsation of the interior and exterior lights. All you have to do is open the door while the engine is running and notice the dome lights and floor lights pulsate. I have not had time to get underneath to check the grounding straps.

Another odd thing happened, my right front headlight bulb died about a month ago so I replaced with a new pair. This morning while driving into work, I noticed it was out again??!! The bulb broke apart inside the housing after only a month. So, I am thinking this might be related to my electrical issues.
 
I've already replaced the alternator. My mechanic was pretty sure the voltage regulator was the problem, but I did that and nothing changed. At this point with the suggestions that have been posted, I need to take a better look at the grounding straps and any other grounding points that may have been missed after I got the motor rebuilt.
 
Look at the ground strap just under front right side. The wires that go to the starter are run in the same place. Check that gound strap. The alt cured my problems on my 91 and 94. Lights would pulsate at idle only
 
When you replaced your alternator, did you fully recharge your new battery BEFORE driving it. The new alternators are not built to recharge a low battery. The alternator will quickly burn itself out trying to recharge a weak battery.
 
SCBird1, the voltage regulator is inside the altenator and yes it is serviceable, I replaced mine myself.

iaragon, You say this happened after you had you motor rebuilt? Well I had my motor rebuilt and I now have this exact same problem, my lights do the disco strobe too. I Took my altenator in to get bench tested and they said that its fine, and told me to bring the car in. So, I took the car in and they tested the altenator and said that it was generating A/C power :confused: , which to me sounds like bad diodes in the altenator. Then I had the altenator bench tested again by a different mechanic under a high load and he said that it was operating fine.
So, since youve replaced your altenator and have the same problem still, im pretty sure that my altenator is fine too (by the way, ive also recently replaced my headlight switch).
To test your grounds try this: jump neg. battery terminal to a good engine ground; jump good engine ground to good chasis ground; and jump good chasis ground to neg. battery terminal; all with jumper cables (you may need 3 pairs, or if possible, 2 pairs). Then start the car and take the cables off one at a time, when the lights start flashing again (provided that they stopped flashing with all cables connected) youll know which ground is hooped.
I havent had chance to try this yet, but i did clean all of my ground strap connections and still have this problem.
Let me know what happens
 
It would be beneficial to isolate the lighting circuits from any accessory circuits. Can you see any erratic movement in the guage needles? Anywhere you can tap a line with a voltage meter to check for variance?

Was the alternator you replaced yours with a new unit, or rebuilt? Was it stock? Who made it? Sometimes the regulator is not replaced in a rebuilt unit.

Does your ignition switch act at all strange? These can be the cause of a lot of problems..
 
I wouldnt mess with that japanese part. Take the thing back and tell them you want another one. I am almost positive your problem lies in altenater. When they test these they looks at how many amps and voltage at a higher RPM then when your at idle.
Good luck
 
SCbird, what your saying does make sense, but under high rpms i still have electrical problems. my amp cuts out when rpms get higher but the lights do seem to be ok.
if i step on the gas and gradually increase pressure to slowly climb rpms, i can get to about 4500 rpm without the amp cutting out. but if i punch it hard the amp cuts out way sooner, about 3000-3500 rpm. im thinkin that the draw to power the injectors at high rpms and a bad engine to chasis ground is causing this.
any thoughts?
 
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