'74 911 electrical gremlins (video)

[Hotwatermusic]

1974 Porsche 911 electric gremlins - YouTube

Figured it was easier to film it so you guys can see it than try to describe it. Basically upon start-up my tach went nuts, radio cut in and out (you can hear it doing so) and my e-brake light flickered. All this, along with an odd drop in the idle every second or two. Only after I rev'd the throttle did it seem to settle down to normal. Any idea whats going on? Thanks!

[timmy2]

If you are lucky and car is still stock, it is just your remote mounted voltage regulator, if unlucky it is your alternator.

[Hotwatermusic]

Car is not "stock" per se. It has an 83 SC motor in it. But that motor is stock. What are the other symptoms of a bad alternator? I thought the alt light NOT going off after 2k RPM was the first sign? My light always goes off. Also, if I have a 74 chassis and 83 SC motor, would the remote mounted voltage regulator be something that would have carried over after the engine swap?

[Hotwatermusic]

About that remote mounted voltage regulator, this is the first I've ever heard of one on a 911. Where would I find it on my car?

[timmy2]

Look beside the CDI box in engine compartment, original VR if being used will be mounted there with wiring coming from engine harness. I'd assume the '83 alternator has an internal VR unless it was changed out.

[Walter_Middie]

Where would I find it on my car?

#6 is the voltage regulator with a 3 prong plug. As timmy2 says, the 3.0 probably has an internal voltage regulator. Make sure you aren't using both the internal and the #6 external VR.

[johnman001]

You need to check grounds. Since your tach is bouncing erratically, check the ground wire on the back of the tachometer. If the wire broke off at the female spade connector, it could cause a floating ground for the tachometer and it will bounce around and be inaccurate.

I really feel you have some grounds that are not properly grounded.

[pete3799]

If your alt. is over charging the idiot light won't tell you.
Put a volt meter on the battery or plug one into the cigarette lighter socket.
High voltage spikes could be causing this.
If the alternator is internally regulated you may still have the external reg. in place but not plugged in.

[manbridge 74]

Multimeter for the facts!

[Amochosto]

Originally Posted by pete3799

If your alt. is over charging the idiot light won't tell you.
Put a volt meter on the battery or plug one into the cigarette lighter socket.
High voltage spikes could be causing this.
If the alternator is internally regulated you may still have the external reg. in place but not plugged in.

What voltage would be worrisome in this respect?

[pete3799]

Anything much over 14.6 or so.
If it spikes over 15 volts i'd get it checked out.

[Amochosto]

Originally Posted by pete3799

Anything much over 14.6 or so.
If it spikes over 15 volts i'd get it checked out.

Thanks Pete.