Battery Terminals and Tire Pressure
 

Ok, before I even start, I will accept all criticism about my lack of knowledge about my car. I deserve it all!

However, I need some simple information/advice. I have a 1995 Carrera 4 that I am getting ready for the driving season. Last November, for winter storage, I pulled the battery and pumped the tires up to maximum pressure to minimize flat spots.

Now I cannot remember which battery cable is positive, and like the fool I admit to being, I did not mark them. I seem to remember it is the rear one toward the back of the compartment, which appears to be a heavy wrapped bare metal cable. The forward one appears to have the ground wire in addition to the cable. The manual is no help. Anyone know if my memory is correct.

Also, please tell me what you use as front and rear tire pressure. Tires are 255's and manual suggests 36 psi front and 44 psi rear, but I recall my mechanic suggesting something else. Again, I did not make a note.

I hope if I fail to record the correct information again, when I ask these questions next spring, you will all be very patient with me.

All kidding aside, any info would be greatly appreciated, as it is Sunday, and I cannot call my mechanic.

No, the bare metal cable in back is your ground. Look at the cable - it goes straight to the chassis (that's the negative).

If you have 17s on the car the book spec is 36 psi all around, but many others with good pressure advice here. The 44 in the rear is for the 16 inchers I believe. that still sounds a little high...

dave

PS - if you're facing your trunk, the battery typically has the poles to the left, putting the ground/negative toward the back of the compartment (so that's the only way the cables will fit).

dave

Yes, the negative cable is braided copper wire, bare, and ~ 14" long - to where it visibly bolts directly to the chassis ( = ground): also, the battery terminals are of two different diameters IIRC - so it would be tough to put the small one on the big post :)

If still in doubt, pls post a pic before connecting, as the DME & other modules are $$$$ to replace if they see reverse polarity.

Are you sure you're running 255's on both front and rear? Please give us the complete size for fronts and rears as shown on the sidewalls. Then we can talk pressures.

If you look @ the tops of the cables, they have a (-) & (+) on them. The short one that bolts to the body is ALWAYS ground.

I run 34-38 front & 40-44 rear on my C4, depending on the track & weather. On the streets I run 38/45, I get good wear & good MPG.

No need to mark them.

OK, you've already done it, but this is for the next guy...

See that copper colored cable (cause it is copper) that has no insulation on it? That is the ground cable. A positive cable will always be insulated. The other one that has black insulation on it is the positive.
http://edelweiss.smugmug.com/Cars/19..._5c2KG-L-1.jpg

And this is what it should look like when the battery is installed...
http://edelweiss.smugmug.com/Cars/19...36_3Vyki-L.jpg

And so that you don't make welding a new career, when you install a battery, the positive gets connected first and the negative gets connected last.

Thanks for all of the info and help, and not one sarcastic remark about my auto knowledge! Battery question has been answered. I am running 205/50ZR 17's on the front and 255/40ZR 17's on the rear, Bridgestone Potenza S-03's. Those were the tires on the car when I bought it. Does that affect the tire pressure question?

The Porsche owner's manual calls for 36 PSI front and rear for that size. I have those tires as well.

The only dumb question is one not asked (or asked before using search :) ). On the battery front, given all the possible downsides to getting it wrong, asking was the right call.

Hazing on the forum is a right of passage and part of the (virtual in many cases) camaraderie of rennlist. And makes for some of the funniest threads.

Always remember to never ever show anything else in a picture of an item for sale (shoe (s), spouse, pet, beer of any kind).