[Eli]

At the last DE the alternator on my SC went out. After doing some troubleshooting and with Noah's and Chris's help we tracked it down to the faulty VR.
Ordered and replaced the VR (internal), the light stays on getting brighter with increasing RPMs. While running under 2000 RPM the draw on the battery is approx. 13, over 2000 RPM closer to 14-14.2 Ordered a Bosch replacement alternator, put it in last night. Now the dash light is solid red , does not get brighter of dimmer with increasing the RPMs. The 9V battery in my voltmeter is dead, so I wasn't able to check the draw...
I've checked all the connections to the alternator, and replaced the ground wire from the block to the housing, as it was very brittle. Crawled under the car, the ground strap on the transmission is in good shape, so are the wires going to the battery terminals. The battery is brand new interstate T-91 (I believe), and is fully charged....
Any ideas?

[Eli]

This is the only reasonable explanation I can come up with....towards the bottom of the thread there is a bulletin stating one must install a resistor for the bulb in the dash....

http://forums.pelicanparts.com/showt...rnator+and+img

[Jazzbass]

Well, battery was going to be my first comment - make sure the the battery is full charged.

What's the voltage in the car when running? Does it change with RPMs? Do you think the car could go on a 15 mile drive? I'd like to get it to my house and we can start troubleshooting from there. Let me know. I have a vested interest in getting this car running .

[VaSteve]

Originally Posted by Jazzbass

I have a vested interest in getting this car running .

Hmmm....

[Eli]

I'm going to check the voltage tonight, couldn't do it last night as my voltmeter batter was dead...
The more I think about it the more I'm inclined to say it's the 2 watt bulb in the dash, but will confirm tonight by checking the draw on the battery

[Trak Ratt]

Jase007 had a similar problem with the Alt. light staying on after getting his Targa back from body shop. Turned out to be a bad “suppressor” for the radio. His thread is still relatively new.

[Cliff Claven]

Originally Posted by david riley

Jase007 had a similar problem with the Alt. light staying on after getting his Targa back from body shop. Turned out to be a bad “suppressor” for the radio. His thread is still relatively new.

Here it is (scroll down to his post beginning with "HA!"): http://www.dorkiphus.com/porsche/sho...0&page=2&pp=10

[Eli]

Being that my regulator is internal where could I find this "suppressor"?

[kimlangley7]

I have a 80 911SC and have had several "issues " with alternators.

After the origional alt went kaput [think it was a Marchal??} > and I didn't want to spend the mega-bucks for a OEM exact replacement > I opted for the Bosch replacement that had the built-in voltage regulator.

There was a resistor that you had to install across the indicator light with the "new" alt or else the voltage reg ligght would actuate.


Have also had the light come on for overvoltage ... tach went crazy too..

[Jase007]

Eli:

What year is your SC? I ask b/c external regulators were used until / through '81. The VR and the RNS [radio noise suppressor] are on the left of the engine bay where the wire from the alternator comes out of the harness. Typically, this wire goes into the RNS [three wire plastic male piece] and a short connector goes from the RNS to the VR, again with a 3 wire press in plastic male & female connectors.

If your SC is '82 / '83 and / or someone has replaced the alternator with a Bosch before ... you rsetup may be different. If it had already been converted to an interal VR and was a Bosch then you need to reference the technical update to add [solder] the diode or resistor [I think] on the wiring behind the guage with the always on red alt. light.

That interstate battery is a MPT - 91. The 91 is the group. Just replaced my redtop optima and the temporary "economy" I was using in the '76 with the same battery. Have you seen the size of the MPT-93 Interestate that is technically "supposed" the be in there . No thanks.

From the other thread:

Lorenfb on PP BBS [www.systemsc.com] had suggested,


Quote:
The noise suppressor blocks (in-line to regulator) have been known to be intermittent (open to alternator) causing a no-charge condition. So, leave
them off, if noise is not a problem.



Also thought this quote of his was interesting:


Quote:
Internal reg. alt. is a mistake! Buy two if you go ahead with the internal reg. one. [in reference to the Bosch units] Keep one as spare in the trunk. That is the worst alt. Porsche ever used. It's just 5 amps more than the original one. They tend to intermittently overcharge. Get the original rebuilt properly, and it will last another 100K + miles. Also, if you have a reg. problem, it's easy to replace with an external reg.

Good luck with your troubleshooting and be patient...

Jase