Carl Fausett

We've made some nice additions to our engine wiring harness that I want to tell you about:

We had a wiring manufacturer make a run of Porsche-correct color striped wiring for us.

We have upgraded our loom to use liquid silicone-rubber over fiberglass material. Stronger, more flexible and yet more abrasion resistant than the OEM loom. Plus, we now seal the ends of the loom with vulcanizing tape that bonds with this new loom to make a water-tight seal.

Our harness, as before - has larger wire in the critical alternator output runs from the alternator to the starter and from the alternator to the forward battery post. The stock wire size there is 10 mm(squared) and the wire we use is 13 mm(squared). This is a benefit to anyone fitted with a larger, more modern alternator or anyone who thinks they may be installing one in the future.

This is in addition to adding more German connectors in stock - all our connections are crimped AND SOLDERED wherever they can be (there are three crimped and shielded connectors that cannot be soldered, otherwise they all are).

...and, I have been able to keep our prices unchanged.
$585 for 16v and $729 for 32v

More information here: https://928motorsports.com/parts/wiringharness.php

FredR

Carl,


Nice kit- not wishing to pick any "fly sh*t out of the pepper" here but a polite enquiry as to whether you may have a "typo" in your post- as I am aware the stock cable from the alternator to the "hot post" is 16mm2 on my model year at least- it then splits into two 10mm2 cables as it leaves the post back to the central electrics. The cable feeding power to the ABS unit is 10mm2 - maybe that is what you refer?

Rgds

Fred

Carl Fausett

I'm glad you brought this to the front.

I should have clarified that when we are talking about the 10mm2 alternator wiring, we are talking about 1978-1986. We use 13mm2 welding cable in it's stead, as the welding cable is more flexible, has more strands, and better abrasion resistance.

According to the WSM, they started using 16mm2 alternator output wiring in 1987. I would have thought that the larger alternator output wires would correspond to the end of the 90 amp alternator in 1984 and the start of the 115-amp alternator in 1985, but it doesn't.

FredR

Good stuff! I know mine is made from 16mm2 cable as I was looking for a means to crimp a connector to make my own as it were but found a place in town that can do it as and when needed [probably 5 years ago!]. FYI - I was thinking of beefing it up to 20mm2 there or thereabouts to fit an auxiliary fan or two.

Rgds

Fred

Carl Fausett

The next common step-up for 16mm2 wire is 21mm2. We are testing it now - fitting the 21mm2 wire into the starter lug and the alternator lugs are no problem. But fitting it into the lug for the forward post is a bit of a bear.

Then there is the question of whether an upgraded wire size to the 16mm2 wire is even necessary...

FredR

I can imagine a potential issue with the bigger cable lug that may need some easing [1mm?] of the receptacle with a dremel.

Both my 928's [90 S4 and 92 GTS] have the auxiliary a/c unit fitted that has a fan. What I noticed with my S4 10 plus years ago was that during summer season at nights with the full beam, full a/c blowers & fans running flat out the voltage needle would run at a debit until the motor hit about 3k rpms suggesting the system was "stressed". Add to that I had a chunky amplifier fitted by my PO and one concluded that the system was stressed.

I studied the wiring diagram and saw that most of that power was running through the 16mm2 cable except the fans that have dedicated cables. Thus adding extra load from the hot post might be questionble. To be fair on the GTS I have not seen these signs but then I do not use the rear a/c [my daughters are fully grown and doing professional jobs so the rear seats no longer used] and I do not have a hairy amplifier to drive. If one were to fit some LED headlamps then a bigger cable would probably not be needed but if one wants to add 20 amps to the stock loading for an additional fan then it becomes more questionable. Interestingly this very issue came up in a recent thread in which Dr Bob pretty much confirmed the same thing when wiring such so figured I must have been on the right lines. His lateral thinking suggested running a fan cable from the starter motor terminal- never thought of that one but easy enough to do!

Rgds

Fred

Alan

When you are running... and if the alternator can keep up(?)... all the current comes from the alternator over these cables - so bigger is better. The remote feed fans come separately from the battery on S4+, but until the voltage drops below ~12.6v - all the current is still coming from the alternator, so the alternator feed to the starter AND to the jump post over this loom are both critical.

Porsche undersized the conductors slightly - copper is (& was) expensive.

Alan

Carl Fausett

if you think that a 150-amp alternator puts out a constant max-output, but it doesn't. Given under-hood temperatures and the closeness to the exhaust manifold, the alternator will be producing less than its SAE bench-rated output numbers always. Secondly, no load should so high that it would require max output from the alternator for very long.

I bet they sized the wires for most likely rated amp load, plus a safety margin of 20%, which would be typical. Saving weight was more likely their goal and not the cost of the wire, but that's just my opinion.

Remember Porsche was calculating based on all new electrical parts and wiring. We aren't so lucky and the impedance in the system is climbing with age.