Need help with my 911 (electrical)

MinusF117 · 01-22-2007, 08:14 AM

I got back from about a 3 week vacation and a little while after that I pushed the porsche out of the garage to jump start it. (1984 911 3.2)

I wasnt paying enough attention and I left one end of the cables on the ground and i connected the other end to the dead battery. Unfortunately I thought I had spaced them out, but they were touching. They sparked and shot power through the chassis actually giving my back a shock which was touching the hood.

Needless to say the battery was shot so I got a new one. I put it in though and it didnt spark or anything when i put the positive cable on. Usually it does right? Well i just got back from looking it over and it does make a clicking sound when i put the positive cable on.

I have no electricity in the car even with a new battery, no gauges, lights, nothing. I havent had any power since the last time i started it before i left. Also, the car was not running when i put the cables on and they sparked, i thought the battery was totally dead.

So far I have checked the fuses in the front hood area with a diode tester and none of them are blown. I also put a diode tester on the negative terminal of the battery and the chassis and it didnt beep and the reading was like 100 something.

Anyways if anyone could help me with a general direction that would be awesome. I am thinking the negative cable is bad possibly because shouldnt there be a short from the negative terminal to the chassis?

Porsche_monkey · 01-22-2007, 09:22 AM

Do you have a voltmeter?

MinusF117 · 01-22-2007, 09:28 AM

yeah, thats what i was using with the diode test. its not that great but it works. What should I be looking for?

Porsche_monkey · 01-22-2007, 09:30 AM

Check your battery voltage first, it that's okay make sure you have voltage at the fuses.

Try turning the headights on when the key is in run. See if they go dim when try the starter.

It doesn't seem likely that you taosted the battery from your description of the 'incident'. That shuold kill a battery. Maybe something else happened....

MinusF117 · 01-22-2007, 09:34 AM

battery is good.....i took it back to the place and they tested it and its good, brand new too. Ill check the voltages but when i say i have no electricity i mean it. I have no headlights no cabin lights, gauges, cd player......nothing, its lifeless.

Porsche_monkey · 01-22-2007, 09:43 AM

Measure the battery voltage, don't trust Jethro at Autozone.

Jethro: no offence intended if you own a Porsche..

MinusF117 · 01-22-2007, 10:29 AM

12.53 on the battery fuses are either 12.05 or 12.5 for the last five.

Porsche_monkey · 01-22-2007, 10:31 AM

And you are sure you have no blown fuses? Did you measure the voltage on both sides of each fuse?

MinusF117 · 01-22-2007, 10:44 AM

yes, all fuses are good but just checking the last one reads 10volts on both sides, thats normal right? its the windows and sunroof i think. Are there any other fuses?

I checked all the ones in the front near the battery

MinusF117 · 01-23-2007, 04:35 AM

anyone? maybe ill just take it to a shop?

Porsche_monkey · 01-23-2007, 04:43 AM

Are you sure your ground cable on the battery is okay?

And no, 10 volts is not normal. Measure from the fuse to 'ground', then from the fuse to the battery negative.

You can fix this, just take your time...

ben parrish · 01-23-2007, 04:53 AM

How could you have 10 volts at the fuse panel if you have no power?
Anyway, 10 volts is not sufficient; sounds like a ground problem. Remove and clean both ends of your ground cable. Look for corrosion at the contact point with the body.
If still a no go, do the same for the positive terminal.

This will be an easy fix if you just go through the steps.

MinusF117 · 01-23-2007, 05:15 AM

well its all 12 volts except for the last fuse which is 10. Its the smaller fuse closest to the cabin. The connections at the battery are clean. Where does the negative cable go? It goes through the firewall i saw but i dont have much room or light where im working. I was measuring the voltage from the negative battery post to the fuses. Thanks for your help guys, Is it ok for these engines to sit for a while like this?

Porsche_monkey · 01-23-2007, 05:19 AM

Sitting isn't the problem.

If you have a bad ground it will show up as a voltage differnce between your fuse and the negative post, versus the fuse and the vehicle body. Try making those two measurements. And make sure the screw is tight on the supply wire to the fuse that measures 10V.

MinusF117 · 01-23-2007, 05:42 AM

Cool, ill do that. I didnt mean sitting would be the problem, just asking if its ok for them to sit over a month without being started? I mean I suppose some people store them in the winter which is kind of what im doing, ....just curious cuz i thought i heard they dont like sitting too long.

Ill let you know what i find with those measurements. Where does the negative cable show up?

Porsche_monkey · 01-23-2007, 06:44 AM

I'm not sure where the negative is erminated, I thought it was on the body just below the battery...

Your car should be able to sit for a few months and still start, the only current draw should be the clock.

MinusF117 · 01-23-2007, 07:20 AM

The car is eurospec, dunno if there are any differences. So i was measuring from the negative post and i tried measuring from chassis ground like you said and there was nothing, just ambient voltage. I traced my black negative cable through the firewall.

Should I have 12v from the car chassis to the fuses?? If yes then the negative cable is my problem huh? Thanks man, I dont have a bentley yet but ill get one soon.

I looked through the parts here on pelican, and the negative cable they have is really short. Am i looking for the big one or the little one. I have 1 big cable(goes through the firewall) and 2 small ones. Big one i assume is engine, tranny, etc.

Anyways, i think maybe the negative cable was old and me taking it off may have torn it huh? Need german plates or anything PBH?

Gunter · Gunter's Garage

Just follow the neg cable to where it attaches to the body (Ground). Open the ground connection to the body and clean very thoroughly all parts and use dielectric grease when re-connecting.
If needed, remove the battery to make room for this and use a light so you can see.
Ground straps are neglected because of their location, especially the connection to the body next to the battery.
Get the Bentley and learn where the other ground straps are and clean/grease all of them.

Porsche_monkey · 01-23-2007, 07:28 AM

So are you going to replace the negative cable?

rick-l · 01-23-2007, 07:43 AM

Could you be a little more specific about what you originally did? If all you did was short the battery + and - together at the end of jumper cables, (and you are still alive) no harm done.

After this spark did the original battery hold a charge. Did you jump to a rash conclusion the battery was bad?

You would not be able to feel 12 volts so there must be some psych going on there.