Wavering/flashing headlights - next step?

[jstein]

I'm having a (gasp) electrical problem with my newly acquired '79 911SC. The entire 12V electrical system seems to be oscillating - most noticeable while driving at night when viewing the reflection of the headlights - they waver considerably (~2Hz). The battery reads 13.6V when the car is off.

I did some searching on the forums here and decided to try and replace the regulator (external to the alternator). I was told by the PO (well, actually indirectly from the PO regarding what his PO told him) that the alternator had been rebuilt recently.

(As an aside, I believe the car I have used to belong to a previous forum member that goes by the name of "pops" - if anyone knows how I can contact him, I would be grateful).

The new regulator didn't seem to help. Putting an oscillisope on the output of the battery, I note that the voltage before (and after) the regulator change oscillates from ~ 14 to 16v (average on a DVM is 14.9V) Ocassionally (once every 5 seconds or so, the reading on the O'scope hits maybe 16.5 or a bit higher).

These readings were done at idle ~1000 RPM, but don't seem to change much when the engine is running faster.

I have a couple of questions:
1) The regulator I received from Pelican is a single silver unit about 1"x3" with a flange and two mounting holes (see first picture). The unit I replaced was a two piece thing - one was approx. the same size as the new unit, but black plastic - connected to that via a bolt connected to the flange was another (much smaller) silver rectangular can. From this can a three conductor wire connected to the Black larger unit - the charging system plugged into this smaller silver can (see second picture).

This is not at all how it looks in my Bentley manual for an external regulator – in fact, they say to replace it just pull the unit out and pop in a new on. In mine, the assembly has to be removed with a bolt.

Question: Does anyone know what the deal is with the two-piece assembly that I replaced, and if the (new) one I currently have installed is adequate?

2) What to try next? Are there tests I can do on the alternator to see if it is OK?


New Regulator installed:




Old regulator resting peacefully on my driveway:



Thanks in advance!

[jstein]

just rehashing...

[john walker's workshop]

no chance that the alternator is an internally regulated model, eh? most folks remove the external reg when they do that, but not all. only way to tell is to check if it still charges with the regulator unplugged, or unstrap it, pull it out and remove the inner plastic housing over the wires. it does sound like a regulator problem though. maybe that one's not up to the task.

[jstein]

Do you have any idea why the regulator I pulled out has two seperate pieces, while the new one is a single unit?

I don't see any other regulators for my car listed on the pelican site - am I just looking "in all the wrong places"?

[john walker's workshop]

the smaller item is just a noise supressor. you can leave it out of the system. in fact, they often cause a charging problem.

[jstein]

Great - perhaps I'll try re-installing the old regulator without the noise supressor. The older unit it physically larger than the new one, so may indeed be a 'better' one.

As an aside, I notice that the 911 I purchased has been serviced by your shop (John Walker's Workshop) - do you keep records of the service you have done?

[john walker's workshop]

if you have the PO's name, and if it was within 2 or 3 years.