Alternator/VR issue?

tkosier · 12-03-2010, 12:59 PM

I guess it's my turn with electrical problems.

With key turned to acc., no alternator light. Engine starts and idles fine, tach reads 0 rpm, alt light remains unlit. Blip throttle, engine light comes on, tach works but reads about 200 rpm low at idle. Voltage at battery is 13.9 at idle.

From many other posts I assume I have a voltage regulator issue. Ok to replace VR, or should I replace both alt and VR?

Did notice that when checking connections, the wires connected to the side of the positive battery were pretty lose. Could that have caused VR issues.

Thanks in advance.
Tom

wwest · wwest's Garage

With the battery located so far away from the VR/Alternator even a few milliohms of resistance, on either side, + or -, can be detrimental.

Bob Kontak · Bob Kontak's Garage

I am not seeing a problem with your alternator or regulator based on the information you are providing.

You have an issue but not necessarily what you are thinking.

Did you check the light after you tightened the battery?

tkosier · 12-03-2010, 02:55 PM

Tightened all connections, symptoms the same.
Kinda strange that once started, it will idle for as long as I let it with no alt light coming on, and the tach reading zero rpm. As soon as I blip the throttle, the light comes on and the tach starts to work.

Bob Kontak · Bob Kontak's Garage

Does the 13.9 volts stay real steady at idle? If so the alt/VR are ok.

Actually the 13.9 should be steady as you rev the engine too.

If not then V reg should be replaced.

Edit - I went through an alternator change - and trouble shooting a couple of weeks ago. Lots of data but the reasons for symptom where the alternator gets brighter was not well explained - they would say "voltage drop" which was not real clear. I just bought a rebuilt alt/V reg and that took care f the problem.

Edit #2 - I am going to double check my car when running - I think 13.9 is ok but this post says below 14 is not good.......... Not what I remember (checked - Volts at battery are 13.98.)

1985 911 electrical issue - alternator or regulator?

tkosier · 12-03-2010, 03:57 PM

After reading a bunch of posts, went out to garage and wiggled switches, checked connections, etc. Found a blown fuse - number 11 which services instruments. Replaced fuse and everything works as it should.

Now, why did that fuse blow?..
Thanks

Bob Kontak · Bob Kontak's Garage

Fuse 11 on an SC includes the reverse lights. FWIW.

Glad you found it.