Charging question on a 914-6 Options

[db9146]

Well, I have made a temporary conversion of my -6, inserting a rebuilt 2.7S with ITBs, MS3, and distributorless ignition in place of the tired 2.0L. Before putting the engine in, I decided it best to install a new alternator along with a new engine/alternator wiring harness.

The alternator is for a 1965-1977 911 2.0-2.7 that uses an external VR.


and here's the new wiring including a new ground strap to the engine case.


The large red cable goes to the starter, the smaller red wire is D+, the black is DF, and brown is D-.

I thought the problem might be the battery because of its age but when I checked the output of the charging system at the battery, there was none. I replaced some of the dash lights with LEDs but made sure not to replace the GEN warning light, which is not coming on despite the alternator not charging.

Should I next pull the D+, DF, and D- plug and check for alternator output across DF and D+ momentarily?

If there is output, what then?

If not, what's next?

[db9146]

This is getting screwier by the moment......at least in my mind.

Tonight, before I started the engine, I measured battery voltage (new Bosch AGM, Group 48)...it was 13.11. Then I started the engine and idled it up, turned on the headlights and measured again....12.89. Turned the lights off, measured again...12.88. Hmmmmm.

I was about to pull the VR and jumper between DF and D+ when I jumped over and read this doc. (http://www.ratwell.com/technical/ChargingSystem.html#vrtest) on charging system testing. In it, it specifically states not to run this test as it can damage sensitive electronics such as ECUs!!! I''m running MS3x so I'm glad I read that...whew. But I did figure out a way to get a measurement at D+ below.

In the same doc, it gave measurements for ohms across, D+, D-, and DF terminals of the VR:




Next, I checked the alternator harness since I had built it new when I installed the new alternator in the engine last year. It checked out fine as well. Then, with the engine running, I pulled the alternator 3-pin connector loose from the circuit board just enough that I could get a multimeter probe under the connector housing and touch the spades for a direct measurement.

On the D+ pin at idle, I measured 13.7V. On the DF connector at idle (750 RPM), I measured a stable 7.4V, But when I idled up the engine to about 1800-2000, I measured the same 13.7V on the D+ pin and an erratic 3.7 - 4.? on the DF pin.

I believe the D+ pin should be reading the full output of the alternator before the voltage regulator, should it not? If so, then why was I only getting 13.7V? Shouldn't the reading have been closer to 15-16V?