914 Alternator

[DocG]

Pelicans,

I have a 1973 914 with a 2.0. When driving on the highway at relatively constant RPM we have noticed that the headlights are flickering. I measured the voltage across the battery with the engine off. It measured 12.5 V. With the engine running at low idle it measured 12.0 V. When the RPMs were increased to 2000-3000 the voltage increases to 13-14 V. I am trying to understand if it is an alternator or voltage regulator problem. I understand there is a way to short the D+ and DF to see if the alternator is functioning correctly but I am uncertain how to do this. Any help would be appreciated.

[darrin]

can you measure voltage when the headlights are flickering? On 911s, the "flicker" is usually caused by high voltage spikes (16-18 volts) that correlate to the flickers and are indicative of a failed voltage regulator.

Unfortunately, the spikes can be very transitory and the alternator would generally show 13-14 volts at rpm like you're seeing. Amazon/etc sell voltage meters that plug into the cigarette lighter socket for constant monitoring, or, some of the better voltage regulators will record high reading spikes if left connected for a while

[colingreene]

Regulators are cheap, I would replace that first.

[30westrob]

I have seen this issue before and VR replacement corrected the problem. You know your alternator has output since you are getting 13-14 V at running speed.
Rob

[porsche930dude]

and a new voltage regulator will be solid state which is nice

[darrin]

At least with 911 alternators, a failed VR was generally also complimented by worn brushes and slip rings (both fixed through an overhaul by an alternator shop) -- no clue if similar issues exist with a 914 alternator/VR and/or whether the 914 has an internal VR (like my later 911) which requires alternator removal to replace.

[porsche930dude]

Originally Posted by darrin

At least with 911 alternators, a failed VR was generally also complimented by worn brushes and slip rings (both fixed through an overhaul by an alternator shop) -- no clue if similar issues exist with a 914 alternator/VR and/or whether the 914 has an internal VR (like my later 911) which requires alternator removal to replace.

Nope the VR is on top on the relay panel and simple to replace. The alt on the other hand is quite the opposite in both regards