dr bob

Thanks again, Earl. I suspect that we'll have a good "map" of the cable by the time my little project is finished.

Lots of folks comment on "low charging voltage at idle", and resort to new/rebuilt alternators, swaps to bigger/ better/ whatever/ don't-really-fit Delco high-current "conversions", chasing the same symptoms I am looking at. I confess that I also replaced the alternator a year or so ago with a new Bosch unit, even though the meter diagnostics said it wasn't really the problem. The new unit came with 14.4 volt regulator too, and the slightly higher available charging voltage partially masked the symptoms, as did another new battery shortly after the alternator.

I'll put together a deceptively simple diagnostic plan that will help others identify this problem quickly, using any DMM and a length of wire to extend the test leads. I have the method well defined at this point, but a few pictures will surely make the process safer and easier to understand. Some has been discussed previously when we were looking at engine-to-chassis ground cables failing. I plan to work on the car next weekend, and will report results as always.

vze2jshn

I believe there is a difference between 1 gauge, 2 gauge, etc., and 1/0 gauge and 2/0 gauge, etc., cable sizes.

dr bob

There is a significant difference in those sizes.

The routing of the factory cable is very well defined by channels that hold the cable where it follows the contours between the battery box and about a foot forward of the rear wheel, From that point the cable is held in place along the tub with P-shaped retainers that are anchored with small screws. At the front, the cable goes back towards the starter just aft of the front left wheel. It's bundled for a short distance with the wiring from the front of the engine, including the lead from the alternator and the trigger wire for the starter solenoid. I'm not keen on bending the channel open for a fatter cable. The little tongue tabs that keep the cable in place are fragile per Rob, and the factory replacement P clips are NLA. The channel provides a certain amount of heat shielding, plus there are addition sleeves placed strategically along the cables length where extra protection from heat or abrasion are needed. Hence the referral to the new factory cable as a realistic option for many.

For most owners, a factory cable or a new fabricated 2-gauge replacement cable is more than adequate. Maybe folks that have monster audio units tied directly to the battery can take advantage of a bigger cable. For the rest of us, the cable needs to carry starting current to the starter, then carry charging load plus fuel pump load plus cooling fan load when the engine is running.

Joe F

Dr. Bob,
I have an '83 Euro and the clamps that hold the cable are nylon blocks that needed to be hogged out with a dremel to accomodate the 1/0 cable that I used to replace the factory cable.

I too hotted up the alternator. I went to some off-road guys shop in Portland and they built one for me. I now can sit at a traffic light with lights on, defroster on, radio on and wipers going and the inst. lights no longer dim with each flash of the turn signal.

It was a bit tough to install, but well worth it. Good Luck.

danglerb

I think most problems are due to the connectors or corrosion on the wire near the connectors, not the size of the factory wire.

2 gauge should be plenty big. Amps for the stereo are going to be wired directly off the battery clamp, all we need to worry about are factory bits unless some huge fan has been added.

Whats the best way to hook up the secondary power lines to the battery clamp that go to the CE panel, stereo amps, etc?

Alan

The best way is very different from stock. I think ideally you have one extra large wire bolted to the battery lug that goes to a fuse panel right in the battery box that directly fuses anything else that needs to be fed directly - this should include the direct CE panel feeders - that go unfused through the car stock...

Porsche did a very bad job on that IMO...

Alan

danglerb

Would something like this 4 circuit 15 amp fuse block from Summit work, or do we need more amps and a lug instead of a clip?

Alan

Something like that would probably work - but check the amp ratings. You'd need to make up a buss bar for the power side to go to a single big wire to the battery lug and then find a way to protect it - say wrap that side with a plastic cover.

I did something similar with a 30A per circuit Hella 6 fuse bank and a steel strap buss bar with holes drilled for each quick connect terminal - soldered into the strap - the strap can take a single bolted on ring terminal to connect back to the battery lug. I also wrapped that side of the fuse bank with a plexiglass cover.

Alan

Rob Edwards

One more cable length data point, I measured one at Mark's today, Pichai said it was from an S4, for whatever that's worth. I got 11' 11" from the center of the hole in the battery post end to the center of the hole for the starter lug bolt. The cable had taken quite a set in some places, so it is likely an inch or 2 longer than what I was able to measure.

Mark Anderson

For some reason Porsche shows a somewhat low list price of $148 on the 90-95 positive cable compared to the $332 on th 87-89.

dr bob

Mark--

Can you tell a difference? My '89 has a slightly different positive battery termainal arrangement compared to the picture Rob shared of his '90 piece. The later part looks more substantial there. Otherwise, same battery location and same starter location so I'd have to speculate that the lengths are the same. I'll be looking at the aggravation $factor$ for making a cable, and might be down to grab the later one if it will work.

Rob--

Your measured number matches nicely with the 12' 3" length that Earl shared.


I do have several pieces of surplus welding cable in various lengths-gauges-colors available, a crimper, plenty of shrink sleeve, a lift, and a car that isn't as reliable as it needs to be. In 14 years of ownership it's only stranded me once, and that was in my own garage when I was gone for a couple months and the battery gave out. The episode at the hospital a couple weeks ago was the closest it's ever come to not getting me home. All over a tired battery cable. I have to count my blessings, and pray again to the preventative-maintenance gods who watch over me and guide me in my ownership journey.

Mark Anderson

Sorry but I do not have either in stock and I just checked with Porsche and the 90-95 is NLA

dr bob

Just my luck-- almost free whenever there aren't any and I need one.


Looks like a trip to West Marine is in the cards for Friday.

dr bob

So I made it home late last evening from my little east-coast project. Decided a good recovery-day activity might be to get a few cables and connections made to do the "how-to" on diagnosing the battery cable fault.

Without touching the car or even lifting the cover off the car, I fab'd a charging harness with fuse in ten-gauge for the battery well. Also made an extended cable that plugs in there or in front just because I had the cable and the soldering station was plugged in. Then carefully, without disturbing anything but the bolts on the battery cables, I installed the charging harness. Lifted the car, pulled the pans, connected the volt meter to the starter terminal and the battery end via the new harness. Reconnected battery ground strap to frame. Look at meter, turn on parking lights. Should be about a 5-Amp draw, and measure a similar 5-Volt drop exactly as it did a few weeks ago. But Noooooo. 15 MilliVolts drop. Head-scratch. Raise car again, with meter attached and parking lights still on. Wiggle and flex the battery cable at the starter end, the Most Likely Place for flex failure. No change. Ditto the cables in the well, and also the ground strap just because. No change. Move meter to front cale, the one from the starter to the jump post. 35 MilliVolt drop, as expected with the smaller cable.

I've been chasing this erratic voltage-drop problem for a few years now, per my battery-purchase log, so getting the diagnostic meter reading right after the last episode is hopefully the guidance I need.

Course of action: I'll get a new cable made tomorrow, along with some (15 I think...) larger cable P-clips if needed for 2-gauge cable. On my S4, these are metal strap type with the rubber-hose-style 'grommets', rather than nylon blocks that Joe F reports from his earlier car. If there's a way to put a 1-gauge cable in there (guide channel width limits OD) I may go that route just because, and I'll replace the ground strap at the same time even though there's no evidence it has any problems. Looking at the positive cable routing, I'm thinking a couple hours should be enough to get the old one out, new one in and dressed up nicely.

More news when it happens.

waynestrutt

If you are making your own positive battery cable it is better to use a cable with as many strands as you can find (ie welder cable, 27 strands or more) rather than household 1/0 6 or 8 strands .Current whether ac or dc tends to flow on or close to the surface of the wire rather than through it. Multistrand wire thus will have more surface area to allow electrons to flow easier without resistance and creating heat which can lead to melting insulation and worse ….Auto wire, as we all know, is multistrand not to make it flexible, although that is helpful, but to make it capable of handling 15, 20 or 30 amps.
Another reason the alternator cannot handle the current demand is the fact it never gets enough cooling air. Heat increases resistance in a conductor and the windings in the alternator are affected and the voltage regulator cuts out sooner. Check that the cooling hose is clear, not crimped and routed properly. An additional heat shield between the exhaust manifold, the block and the alternator will help. Also, as all have noted in many other posts ,the ground strap and all the scattered other grounding points on the chassis need to be checked and made secure.