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Dr. Hamman
Dr. Hamman, Technician
Category: Classic Car
Satisfied Customers: 2436
Experience:  I have 30 years experience repairing, restoring, and customizing cars, and pickup trucks.
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I'm working on a 1971 350SL Mercedes (107 043). The

Customer Question

I'm working on a 1971 350SL Mercedes (107 043). The charging light on the dash is glowing, dimly, while the engine runs. With the key on, engine off, the charging light is normal brightness. But when the engine runs, the charging light does not go out.
Rather, it glows, dimly and constant, but does not go out. The dim glow appears to be the same at most rpms. Battery voltage with ignition off is 12.3v. A quick voltage check of voltage with the engine running is 12.3 to over 15v, depending on the engine rpm
(tried up to about 2500rpm). I had just replaced the alternator and stand-alone regulator. Charging system/charging light behaved fine for a while; i.e., the charging light went out normally. The steering wheel had been removed for some unrelated work. When
the strg whl was reinstalled, and the car was backed out of the shop, the horn would honk as the wheel was turned; i.e. without pushing the horn button. One of the carbon brushes had broken, apparently causing the horn malfunction. However after the horn brush
replacement the charging light glowed with the engine running. Related? Don't know. Horns themselves work, fuse 5 is good. I would guess that there's something wrong/different about the new regulator. How do I handle this problem? Thanks
Submitted: 2 years ago.
Category: Classic Car
Expert:  Lou P. replied 2 years ago.
Here I am. Let me know if you want to proceed later. I have to get my old manuals out. Don't have them at the moment.
Customer: replied 2 years ago.
Hi Lou. I've ordered another voltage regulator, but it was only an (educated) guess. Would still like your input.
Expert:  Lou P. replied 2 years ago.

Ok I'll get with you later and see what we can figure out.