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"Strobing" dash lights and headlights

595 views 9 replies 7 participants last post by  ErikBerglund 
#1 ·
Hey Peeps. '87 560sl.

Once every 5-20 minutes the headlights and dashlights will vary up and down rapidly as to brightness. Usually only lasts three to 15 seconds, but varies.

May be RPM-dependent, but don't really want to pop it in neutral at highway speeds and test it out.

Belts are great (new alternator belt; nice and snug), battery is new: is my alternator going?
 
#4 ·
Yeah guys, probably not the battery. But really appreciate your input and time.

And I hear what you're saying about instrument grounding, but that wouldn't carry over to the headlights. Pretty sure it's system-wide rapid fading in and out of power (but just substantial dimming back and forth--nothing goes on or off).

What I'm wondering is: is this what happens when an alternator goes on a 190k mi car? Just did the belts and the bearings seem fine and it spins fine, but can the magneto die on the inside or do they ever act like this when an alt goes bad?
 
#9 ·
Measure your voltage when engine idling, light and AC on. You should have > 13,5 V. If low, the voltage regulator on the back of the alternator is a wear item and is easily changed. At your mileage I would change it anyhow if you don't have previous records.

Also check for corrosion on fuses.
 
#10 ·
Thanks mate. This (and all other) replies were very helpful. Voltage to battery barely upped at all at engine off versus idle or 3k RPM.

Thinking voltage regulator is it. This is, alt pulley seems to spin fine in the hand with belt off, but had a weird issue with a new alt belt being thrown for no good reason with a bit of melted plastic on the inside of the pulled only 100 miles ago (quite possibly accumulated from belt, but could not tell once it was thrown/damaged).

Thinking at 190k mi I just go with (a lot) more cash for a reman'd Bosch alt. Or--as the alt seems to spin flawlessly at low speed and I can't trigger any hesitation/bad signs from the bearings, should I save $175 and just to the voltage regulator first?

Best (and thanks again),

Erik
 
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