History: 1995 C2 w/80,000 miles. Purchased in Oct 2006. PPI performed by local dealer. Perfect car with the exception of a bad alternator. Said alternator was replaced at time of PPI. Now for the jucy part:

I've put approximatly 1200 trouble free miles on the car since I purchased it. Tonight I take it for a little drive and here's what I noticed. I turned on the brights and the radio (aftermarket Pioneer DEH-1400) popped and shut off, then turned back on. The radio presets were erased. Subsequent "brighting" made the radio pop, but to a lesser degree up to the point where there was no additional popping. The car had been driven earlier today with no lights or radio turned on. Also noticed low beams might have flickered once or twice during my rather spirited 20 minute drive. No other problems noted except maybe a slightly slow engine crank on start up- maybe. When I shut the car off, I could hear a ticking sound comming from somewhere in the cabin. Being rather new to the car, I brushed it off to the clock. (key was out of the ignition)

Thirty minutes later, I go back to the car and notice the dome lights will not illuminate. The car is dead. Very dim lights on panel. I hear the ticking sound and now notice it "ticking" at about .5 sec/tick. Furthermore, I locate the source comming from underneath the passenger (right) seat. I put a volt meter on the battery and it reads about 11.6 volts. Still no dome lights or ability to crank engine. I try to electrically move the passenger seat aft to see what I can see and immediatly see the dome lights turn on bright. Car fires right up. Can not duplicate. What the hell is going on? What is located underneath the right seat? I suspect I'm dealing with a loose connection/short to some black box located underneath the seat. I've disconnected the ground on the battery until I get some more info. Any help will be greatly appreciated.
Paul

 

If the battery voltage and current is okay, it might be the battery earth strap. Take it off and give it a good clean, as well as the bit that it connects to on the chassis. Hopefully it's as simple and cheap as this!

 

To my understanding the alarm system is under the passenger seats.

 

What is the history up to that point i.e. radio install, any other changes etc.

 

You may have a simple short due to a radio upgrade install or something back in there.
It's may be a cheap (you provide labor) , but possibly very time consuming fix. I had a short with an aftermarket glass sensor (which I never knew was there!) tied into a module somewhere it shouldn't have been. Tape came off the wires crossed and with a radio lead when I slid the unit back in, and it caused all kinds of weirdness with my flashers etc.

 

Your problem sounds "global", ie. it is affecting more than one system. An intermittent short whouldn't do this, and it would kill the battery. There have been other ground strap gremlins posted . Searth the forum. Good luck!

 

Thanks all. This morning I reconnected the battery and took it for a drive. No problems. I suspect too, that it is probably a grounding issue. I'm going to have the battery load tested to make sure it isn't a weak battery. I know that most modern cars are very sensitive to low voltage so we'll see what I find out.

 

The crimp on the battery ground strap (where the copper meets terminal) can loosen over time - give it a few good wacks (out of the car of course) when you are cleaning the contacts to eliminate ground fault. If you continue to have problems monitor voltage while driving - it will tell you if the voltage is going low or high....

 

The alarm control unit has a relay that will click on/off if the voltage level gets too low.

 

Can I ask if the engine loom recall was performed? It should have been verified by the dealer during the PPI.

 

Yes, the loom has been updated.

I'm beginning to suspect a bad connection at the battery. I cleaned the terminals and so far so good. BTW, Joel Reiser has responded to my post on PCA.com. He suspects the same as the voltage for the battery was slightly low. He also wondered why the alternator had been replaced and the answer was that the old one was producing too much AC voltage and I believe that was the result of a diode failure. Prior to the alternator replacement, the alarm was doing some strange things like not unlocking, drive bolck system not alowing starter to turn over, etc. Same type of thing seems to hapening again. So..
Maybe I have another bad alternator, and if so what is making them fail? Or, a bad alarm control unit, or hopefully a bad battery connection/bad battery. Again all these symptoms remind me of low voltage issues. If this sounds bad, you should see what a W140 S -class Mercedes does when it's voltage gets low..ouch!

Paul

 

This is exactly what it sounds like. Thanks for the input!


Paul

 

I had a bad alarm control unit ~ 2000. I don't remember it affecting any other system. When it malfunctioned it also wouldn't allow me to put in the code to start the car. I don't remember how I got it running, but I do remember that once it was running I couldn't open the door or the alarm would trigger. Fortunately it's a cab, so I could hop in and out with the top down. Drove to the dealer, who at that time was 1 1/2 hours away. The tech there wacked it a few times and it worked until the new part came in.

 

This is an extremely common problem. Cleaning and reconnecting the negative battery strap will work for a while, but the uninsulated copper braiding oxidizes over the decade or so that it has been sitting in the front trunk, drastically affecting its conductivity. For 15 bucks you can buy a new strap from your local auto parts store (I replaced mine with an insulated one) and you won't have to worry about it again for a while.

 

Yes...

New shocks AND a new grounding strap should be the FIRST things new owners do/check ( :