Dear fellow 911 owners,

After installing a rebuilt alternator from Vertex Auto and a new Interstate MTP-93 battery, I still have slightly dim headlights/instrument lights at idle. Is this a common problem with the 911 3.2 and how is it typically resolved? Forgive me for reposting the same question, it seems some board members didn't realize that I had already replaced both the alternator/regulator and the battery. This is a very annoying problem and I was wondering what steps I could take to tackle it. Thank you very much in advance.

 

Can't help you on the repair- but my 85 DOES NOT dim, even just a little, at idle.

 

Lights dimming at idle does indicate a problem.

Test the voltages in or system. The battery should be around 12.5 volts with all loads turned off and the battery charged. When the engine is running, the voltage should be around 13.5 volts. If you don't get 13.5 at idle, rev the engine and see if the voltage comes up. The easiest place to measure is the terminals on the small fuel panel in the engine compartment. If these tests don't check out, you might have new parts but you might not have good parts.

Another issue, do you have any high load electrical accessories, like a mega-sound system or lighting modifications?

 

Hello

Well it is somehow normal for a old car with old partial oxided contacts in the wirelooms and old bulbs and other little items. This all adds up to little anoying things who are not really a problem. I would just go trough the fuse board and clean the contacts on the lightswitch.

Grüsse

 

It is strange that AFTER replacing your alt you are experiencing dimming of the lights. What is your idle set at? Did you adjust you fan belt correctly to avoid slipping?

I would take Roland's adive. I can't remember a time he was wrong. These cars are getting old. Everyone takes very good care of them, but I had heard of performance increases with the replacement of wire looms. These wires are getting old. But that does not mean yours is bad. Clean all the connectors and fuses. Make sure your idle is set correctly. Check the output on the alt. It is common for the cars to slightly dim at idle and the red indicator light to glow at idle. It is really nothing to worry about. Just do some housecleaning od all connectors.

 

Thanks for the advice, gentleman! The fan belt tension is correct and the alt light does not glow at all. I do suspect that the idle speed is a bit slow but I figured that the battery should compensate for the alternator at idle. It's set at about 950 rpm. Is that about right? Also, someone told me today that he was certain this problem was related to a bad battery ground wire. What are your thoughts on this? Thanks again.

 

G'Day Fassi.
I had replied to your earlier post on this, thinking the dimming was acceptable/normal. I too had replaced the alt, volt reg and battery and still the headlights dimmed a bit.
Well, just this weekend I replaced the indicator stalk due to headlight blackout as I flicked on the high beam or indicator. Poor contacts in the switch assembly I was informed. I looked for about 15 seconds at the suggestion of tweaking the contacts - too bloody complex for me with no guarantee that I'd rectify it. So I purchased a new stalk switch assembly $$$!
As the wiring for this is connected to the dash light switch I decided the very least I could do was pull the wires from that switch and clean up and tighten up the contacts. There's a gaggle of them and they were pretty cruddy.
Anyway, I'd reckon Roland and pbs911 may have it about right. I dunno if it was the dash-switch or the stalk-switch, but after the reassembly my bonus is that I don't get dimmed headlights any more!

Cheers,
Sean.
1980 Hellblaumetallic SC Targa.