1. Several years ago, I replaced the battery in our 84 with a new one from AutoZone. I had the "guy at the counter" confirm the correct amperage of the battery. The result was a battery with proper specs, but which was significantly smaller than the previous battery.

2. Upon placing this new battery in the compartment, I discovered that the OEM ground strap was not long enough to reach from battery post to the ground point in the back hatch. So I purchased a longer, generic ground strap. The strap is not tape-like - more like a cable.

3. I have, in the past couple years, been one of the multitude who has posted here with electrical problems. Notably, I have had voltage fluctuations. Most recently, I've had voltage drops.

4. Recently, I discovered something about the conductivity of this ground strap in conjunction with the hatch ground point. Even though I've scrubbed the ground point, I cannot get electrical to come on just by touching the ground strap to the ground point. The electrical only comes on when I insert the wingnut bolt through the aperture in the ground strap and then insert the bolt into the ground point screw hole. What's more, the aperture in the ground strap is 2-3mm wider than the diameter of the wingnut bolt, and if the inner edge of the ground strap aperture isn't touching the bolt, I get no electrical.

So now I'm wondering if my blips have been caused by the iffiness of this connection. At the point I realized this a few weeks ago, I made certain to tighten the wingnut bolt such that it was in good contact with the inner rim of the ground strap opening. Since then, I've had steady voltage.

Thoughts?

Thanks folks.

Tim

 

Battery Rule No 1 - always fit the LARGEST physical size (of correct spec otherwise)that will fit in the hole.
Then you should be able to use the factory earth lead...
Have you tried cleaning the face of the new strap's connection end? Is it painted or something that would prevent conduction? You need the largest possible surface area in contact with the earth pad, IMHO the strap edge to bolt contact will be way too small for starting current to f low well. Do you know if there is any heat produced at the earth point while cranking?
jp 83 Euro S AT 52k

 

I recommend you purchase the correct size battery and ground cable for that year car. If one is not available from a local or online supplier, you should be still able to purchase one from Porsche.

The battery terminals should be coated with dielectric grease to promote a long service life and the battery voltage should be maintained above 12.6 volts by frequent driving or by using a battery charger/maintainer.

 

WOW... interesting!

Last summer, I jumped in the car (84 928S) to head out and she was dead, not even a door light. Guys on rennlist suggested that it might me a key / ignition issue, though before I could resolve, the electrics came back on by itself and I thought perhaps the key / ignition issue was a freak accident of some kind and forgot about it.

Last fall, I left the lights on all night and ended up with a dead battery. I jumped it the next moring and drove 3 hours to Watkins Glen where she stalled with a dead battery again. After testing everything, the alternator appeared to be shot and I replaced it.

A month or so later, i head out for a spin, and again, much like the first time, there is no current at all, not even a door light, nada... so this time i grab the multimeter and start testing... the battery is strong, so i start testing grounds, and sure as hell there is no connectivity from the battery to the end of the grounding strap... WTF... looks like the strap is shot.

I replaced the strap with a standard cable, though as described at the start of this thread, it does not fit well to the grounding wingnut and circular copper plate. I stored the car for the winter a few days later. A couple of weeks ago, the weather was decent so i decided to take her out for a spin... unreal, my dash voltage meter is bouncing back and forth from zero to 15 and the lights are dimming out all over.

I am thinking that I may have got a bum alternator, though I bet it is that f'n grounding cable connection! So, YES, this connection is very tricky indeed. I bet this screwed the 1st alternator too... I will replace this connection on the next warm day.

 

As JP says, size of the battery is the #1 requirement, unless you're into weight reduction mods. From your description, the strap you have is questionable; you shouldn't have to go through those gyrations to get a connection. I'd say replace it for now with a better quality generic, but when the battery needs replacing get the correct size with a proper OE ground strap.

OSP, you probably fried the alternator on you 3 hour trip to Watkins Glen -- a common occurrence when it is used as a battery charger. The current voltage-bouncing syndrome could be a bad regulator, loose wire, or just an iffy brush connection from sitting. I'd say check all the connections at the battery and alternator and see f 1/2 hour of driving makes it go away. Also, if you can note whether the headlights dim while the gauge is bouncing. If not, it's probably a loose connection to the gauge.

 

Does anyone know the number of the largest battery that will fit the 84 battery box?
According the PET it was the same box 928 501 805 02 79 through 86.
What are the dimensions of the battery box?
Can't seem to find a battery type listed for the 84 year.

 

Roger:

Thanks for chiming in. Here's my homework...

 

Whatever you have installed, sparks should be flying when touching the ground strap to the body (and usually between the ground strap and metal brace on the hatch motor when removing the ground strap )

 

I've got two running heavy aftermarket groundstraps and they do spark on body contact. The body ground point looks to be brass, so should the ground strap BTW to prevent dissimilar metal corrosion at the joint.

On the subject of ground straps, here's a picture of a ground strap that had damage hidden beneath the plastic sheath. Shut the car down.

 

I've been using a generic ground strap for over 2 years and have not had a problem with it since I installed it.

 

I'd like to see this. I'm sure they come in many varieties. Is your ground strap flat or tubular (he asks, shifting uneasily as he thinks of the connotations)?

 

It's a thick, semi-rigid tube, that's longer then most.

Try putting a washer under the wing nut if you really think that's where your problem is.

 

The battery box size was reduced in 1986 models due to changes in the exhaust system.

A smaller battery could be accommodated by a modified battery retention clamp and ground strap extension. Something like this on the ground strap...



http://cgi.ebay.com/18-Battery-Cable...item53df1b3157

Or, just buy a complete new ground strap..



http://cgi.ebay.com/New-2-Gauge-Brai...item3a3a1d4929

 

I also have a generic ground strap in my car that is working without issue. I don't see why it would matter since it is just a simple electrical connection.

 

I am sure everybody hates on Wal-Mart, but I found a direct replacement battery there that had the proper specs and size. The manf. marking were exactly like the one from Interstate that it replaced. I can get the part number off of it if you want. and it was only 75 bones.