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Generator light issues
Posted: Fri Jan 10, 2025 9:07 am
by leewiffen
Morning all
1977 911S The red light in the rev counter continues to glow faintly despite the alternator being reconditioned
It doesn't glow more brightly when revved, although it does when you stall the car and the engine goes to cut out
The alternator is charging, and was charging prior to it being reconditioned which I was advised would solve the problem
Some £800 later, the problem persists
Any good Auto Electricians in Surrey?
TIA
Re: Generator light issues
Posted: Fri Jan 10, 2025 2:14 pm
by PeterK
You haven’t fitted an LED bulb have you ?
Do you have an internal or external regulator ?
Re: Generator light issues
Posted: Fri Jan 10, 2025 2:40 pm
by Bootsy
Mine always has for 20 years in my early car - had the output tested and all is well.
Re: Generator light issues
Posted: Fri Jan 10, 2025 3:42 pm
by Bruce M
Worth remembering how that light works. It is connected between the battery positive & the regulated output. If the alternator is at zero volts (engine off) juice flows from battery positive (via ignition switch) through the bulb. The bulb will also light if the current flows the opposite direction due to alternator voltage being higher than the battery voltage. So check with a multimeter to see what the voltage difference is each side of the bulb (at source or at gauge). Poor connections can cause a voltage drop along the way, resulting in a voltage difference across the bulb.
Re: Generator light issues
Posted: Fri Jan 10, 2025 7:02 pm
by leewiffen
PeterK wrote: ↑Fri Jan 10, 2025 2:14 pm
You haven’t fitted an LED bulb have you ?
Do you have an internal or external regulator ?
No LED bulb fitted and currently checking to see if there is an external regulator
Re: Generator light issues
Posted: Fri Jan 10, 2025 7:04 pm
by leewiffen
Bruce M wrote: ↑Fri Jan 10, 2025 3:42 pm
Worth remembering how that light works. It is connected between the battery positive & the regulated output. If the alternator is at zero volts (engine off) juice flows from battery positive (via ignition switch) through the bulb. The bulb will also light if the current flows the opposite direction due to alternator voltage being higher than the battery voltage. So check with a multimeter to see what the voltage difference is each side of the bulb (at source or at gauge). Poor connections can cause a voltage drop along the way, resulting in a voltage difference across the bulb.
Somewhat above my pay grade this Bruce, but it makes sense that despite the expensive alternator refurbish, I still have the problem. I'll be looking for someone who can do the checks you suggest
Re: Generator light issues
Posted: Fri Jan 10, 2025 9:07 pm
by Gary71
Mine does the same, I worried about it, even bought a replacement alternator and regulator…
Stayed exactly the same…
Now running the original alternator again. Charges absolutely fine over many thousand miles of running with lights, wipers and a heated screen running!
Still annoys me when it glows, but I’m learning to ignore it
Re: Generator light issues
Posted: Fri Jan 10, 2025 10:11 pm
by jtparr
+1….am fairly sure mine stops glowing when you boot it….. 8…..does glow more when at idle…seem too think it glows all the time at night time when you can see the lights’more….I have ignored it for 20 years and with a refurbished alternator…so I just assumed it was kind of normal
Sure doesn’t stop the fun once you get it over 4500….
J
Re: Generator light issues
Posted: Fri Jan 10, 2025 10:13 pm
by jtparr
Or 5,000………5,500….6,000….6,500…7,000….7250……..