KHamrick

I need some help.I have an 04 996, manual with about 92k mile on it. I started experiencing an issue where I thought the battery was going out. The car just wouldn't start. Turn the key and nothing happened, no lights, no "clunk" of a starter but the battery checked out and eventually the car would start. I replaced the ignition switch and thought all was solved. Everything worked for a few weeks and then the other day the car just turned off-complete power failure as if someone had turned off the key. I reached down for the key, turned it as I was coating along and it started right back up. A few days later I go to get out and notice that the lights didn't stay on. Not even the little door light. My son closed his door and door light and all came back on. Tonight I drove to the store but the car would not start to come home. No indication of power, no instrument lights at all except, before I would turn the key, I did get the oil and battery light on. As soon as I turned the ket the lights went out. I called my son, waited a few minutes, dried the key (it's raining), hit the dash board and tried again, the car came on with a small strain. I got a warning that the ABS wasn't working and then a warning that PSM wasn't working. I got home, turned the car off and the window will not drop, turned the key a couple of more times and finally got dash lights again, lowered the window a bit and came in here to beg for help. One more thing, on the day of the power loss while driving, the stereo was on but no sound. When I cranked it back up I got sound again. Maybe the new ignition switch is defective?

Icelia

Could also be a short or a broken wire inside the harness.

check the plug behind the ignition switch.

Next time this happens, (fails to start) wiggle the wiring behind the ignition key while trying to start.

I recently had a similar issue that I thought was the ignition switch, which I also replaced. It ended up being something with the relay assembly under the carpet in the back of the car.

After I pulled them up, reseated the relays and just kinda moved things around, the problem went away and so far (crossed fingers) hasn't come back.

To be clear, my problem was a bit different, ignition came on, but would not start, yours sounds like the ignition circuit itself isn't coming on.

jandackson

Sounds like a ground issue. Check the negative side battery cable to chassis. Make sure it’s clean and tight. Then check the engine ground cable found on passenger side behind the wheel.

also check your alternator connection on the back of the alternator. Lastly, check the other end of the alternator cable (known as Y cable) that goes to the starter, the positive terminal in the engine bay and the alternator. These are known to corrode and become very high resistance.

De Jeeper

A lot of the power goes through the headlight switch too so u may want to replace it. If u search u wil find a bunch of threads about a.new one fixing weird issues.

996-CAB

Electrical engineer here. The Y cable wouldn't cause these problems. I like the faulty ground idea

KHamrick

There is an odd connection on the negative side of the battery. It looks like someone added a bit of extra cable to both the car side and the battery side and they connect to each other with a couple of brass plates that are held together by a larger screw with a green top on it. I have never seen anything like it but I am thinking about removing it in the morning.

De Jeeper

Its a cheap battery disconnect.

KHamrick

Yes-that's the thing. Honestly it is no easier to get on/take off than just doing it at the terminal because the wire is too short to easily slide the male/female connectors together. I am gong to take it off although I doubt it is the cause.

KHamrick

So a couple of more things. Last night when I got it home I checked the lights, my son said when i turned them on the driver's side came on but immediately went out. Today I removed the stupid quick disconnect from the battery and the car started right up. Does that imply that it is fixed? I have some doubt. All the lights work now so I am thinking it is a short in the light or a problem with the light switch referenced above. I did check the engine ground today and it looks/feels solid so I am not toughing it. I suppose I should order a replacement switch and just drive it to see if the problem comes back.