First I will start by declaring that I am a known electrical idiot. I do have a basic understanding however I have thoroughly confused myself.

I have noticed that my car is often dead when it sits there for awhile.

When I converted my car to a 2.7l /6 I had to replace the alternator. I am not sure if my alternator works. It has been awhile however I believe that all I did to hook up the alternator for my conversion was to run three wires from the alternator and connect them to the corresponding posts (D+,D-,DF) on the stock relay board- in addition to a ground wire. I am not certain that this is correct.

Here are some thoughts about problem that I might be having-
-Installed incorrectly?
-bad alternator?
-I possibly just don’t drive the car enough and the battery slowly dies
-maybe I have too many accessories which pull more than the alternator can produce (all I have is an msd 6al and about 10 gauges. I never drove at night so my lights are never on-unfortunately my voltmeter is broken)

Can someone help guide me- either to help me wiring the alternator properly, or help me figure out where my issue is?

I have the same engine in my 914-6 conversion — alternator has voltage regulator in its case — with three wires attached: positive power thick cable to battery (+ve.), thick wire to engine case(ground), and blue thin wire to dashboard alternator warning light ( exciter wire).
My car has a modern digital radio which draws some power when the ignition is tuned off - enough to run the battery down over a few days of no driving. I installed an isolation power switch to provide power to the radio only when I want to listen to it.

Get a VOM (Volt Ohm Meter)....they're cheap at FLAPS. See what voltage you're getting at the battery terminals with the engine off--should be about 12.5 or so. Now with the engine running the voltage should be above 13.5...try it at idle and at 2000 rpm. That will tell you if the alternator is charging the battery or not. If not, then you have a problem with the alternator or possibly the regulator & need more electrical help.
If it's charging OK (meaning 13.5v or more with engine running) then check to see if there's something draining the battery while the car is sitting turned off. Check for voltage across each of the fuses with the fuse pulled out--should be zero if that circuit is not draining the power. If a circuit is draining power track it down step by step. Post what you come up with....

Something's not right here. IF the 2.7 alternator has it's own regulator, but you connected the wire to the original relay board/regulator, something is likely to go up in smoke. Does the relay board still have the regulator on it?

I would recheck your wiring first and confirm the new setup has the built-in regulator. You should be able to run the hot/charging lead right to the battery and take voltage measurements at that point.

I also have a 2.7 in my conversion -6, and the original alternator does use the external voltage regulator (as did the previously installed -4). I’d start by checking and cleaning your connections at the board for the voltage regulator as an easy first step. Assuming your charging light is functioning, I’d start and run the car to see if it goes out while running the car. Another easy, inexpensive test is using a plug in voltmeter that fits into the cigarette lighter socket to see the actual voltage reading. However, if the alternator was swapped out with an internally regulated one, the external regulator should not be used and wiring modifications should have been done. In a -6, I think an externally regulated alternator is a better choice as the alternator is such a pain to replace.Click to view attachment

This is the voltmeter I have mounted in my 911. Purchased off Amazon.

Click to view attachment

Thank you for all of the replies. My alternator has an external regulator. I am going to check things further when I get home tonight.

When I looked at old pictures to see if I had an internal or externally regulated alternator, apparently I looked at old pictures. I completely forgot that I changed my alternator. I just took it out to find that I have an internal regulated alternator. I have three connections: big + wire that goes to the + side of the starter (the starter also had a big + wire coming from the battery), ground wire, excite wire however it’s not hooked up. Unfortunately it’s not charging. Does that sound like it’s hooked up correctly?

The idiot light has to be connected, that's what excites the field in the alternator.

Well, I have made the same temporary conversion to my -6, inserting a rebuilt 2.7S with ITBs, MS3, and distributorless ignition. 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
Click to view attachment

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

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

If there is output, what then?

If not, what's next?

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