I mentioned this in another posting, but now I know of another motor with this issue, so I thought I'd call it out separately.

I've seen some nice rebuilt motor shots recently, where like I did with my motor, the fan shroud has been powder coated. And hey, while we're at it, let's coat everything else, right?

Well, be careful, because your alternator's ground path may be degraded. If you don't remove the powder coating from the interface between the fan shround and the case, and between the alternator brackets and the case, there's no ground path, and you'll develop a back voltage that you can measure at the D- connector on the relay plate.

The solution is to remove the coating and make a clean path to ground. Even under the best conditions, the path from the alternator to chassis ground is pretty long:

Alternator case => Brackets => Fan shroud => Engine case => Tranny => Tranny ground strap => Chassis ground

You can improve the alternator ground path by running a wire (use the same gauge as the alternator B+ connection to the starter) from the alternator case to the chassis ground that's by the relay plate (run it up through the same grommet along with the voltage regulator cable).

I did this on my car after my rebuild. At first, when I measured D- on the relay plate with the car idling (about a 6 A load), I was reading -1.2V. This means my charging voltage (or system voltage) was only about 12.3V, and my battery was only reaching 50% charge at best. After cleaning away the powder coating, and adding the additional ground wire, even with the lights on and a 22A load, I only read -0.06V at D-, a vast improvement. My charging voltage is now 13.6V and my battery is always at 100% charge (12.75V).

I also added an additional ground connection (6 gauge) from the chassis ground at the battery to the nut in the engine compartment that's on the starter motor top bolt. With a fully charged battery, and this improved grounding, my car cranks a lot better than it used to. I suspect that many of the problems people have with their starters not working when hot may in part be due to these type of grounding issues, leading to undercharged batteries and poor current path under heavy starting loads.

You need to do that even with painted parts.

I am sure you are correct about the grounding. Paint or power coating will make a good insulator. I removed an alternator once and had a terrible time with the long bolt. It was so corroded where it went through the hole in the alternator. This corrosion was white and hard. I felt that maybe there was some electrical connection problem that caused the corrosion. Maybe it was because of dissimilar metals (the bolt is steel and the housing is aluminum) I was tempted to install an additional ground strap at the alternator to the engine.

Hey, I'd better post this before Captn' Krunchy chimes in - there are plenty of 914's on the road with no aux ground wire that are working fine. I think the issue only comes up when we go overboard and coat everything in an insulating layer. That said, the alt ground setup isn't optimal, and can be improved a bit by adding a direct ground wire.

It's easy enough to test if you have a problem. Just start the car, let it idle, and switch on the headlights. Take off the relay cover, and use a digital voltmeter to probe the voltage on the D- terminal of the plug on the side of the relay board (connect the ground side of the meter to the chassis ground next to the relay board). The negative voltage you read here reduces your charging voltage by a like amount. If it's significant (e.g. -0.5V or more), your ground isn't optimal.

Sorry guys - another reason why I am NOT proponent of powder coating!

I powder coated all my engine tin, I didn't powdercoat the fan shroud, the alt. bracket was powder coated. Even painted parts have to have the coating removed to make a good ground.

Care to share some of the other reasons? I have coated the tin on my bug and love it. It is durable and looks great. I am about to do the same to my 914 tin...unless you convince me otherwise!

i had mine done with a textured finish. has held up very well.

I painted my fan shroud with a nice silver basecoat/clearcoat, and I had this very problem. My quick, get-to-the-track-this-weekend-it's-not-a-concourse-car remedy was to drive a screw between the case and the shroud. The threads tore through enough of the paint to complete the circuit.
Next time I have the engine out I'll pull the shroud off and clean the areas where it contacts the case.