New to me car, 1991 mercedes 300te

I have the car 20min starts, drives, no problems. Park it.... 8 hrs later D E A D. I jump it, and it fights, but starts up. drive it one hour home, runs fine, just before i turn her off I try the electronic seat adjustment and the headlights dim off and the radio goes out as i touch the switch. i try the window button, i pull up on it as the window is already up, the lights go off again, interior stuff as well. So it seems the alternator right?

i park over night, today it is dead again, so i replace the battery with a new one. put the positive terminal to the battery, and the negative to a test light then to the battery, it glows like a becon. i pull all fuses one at a time and the test light does not go out.

so what could it be?

i am going back out on my lunch break to troubleshoot it again.

mabey it is a relay that grounded??? i have to find the relay board.
mabey an aftermarket radio/ alarm/ po rewire ???
mabey the alternator is grounded??? i have to find that too to check.

how to test the alternator, easy test. it is parked in baltimore, i dont want to walk home to PA tonight.

any more ideas??

the car is currently parked with the battery disconnected untill my lunch break.

Joseph

I feel for you as these are tough cars to figure out electical issues, but consider yourself lucky it is not an S class.

Once you rule out that the alternator is not the source of the leak, what I suggest is that you first start by going through the fuse panel with an Ammeter (could be a Multi meter, but bring fuses along, as this sounds like quite the draw.) and see what is drawing a significant amount of power when it should be shut off.

If this bears fruit, then you need to look at all the components on that circuit and disconnect each one to see which one causes the draw.

Then determine if you can live without it... LOL

I hope this helps.

If you drove home 1hr it is not the alt. The alt is what kept your car running. Did you remove and test the battery at a FLAPS? I bet your battery is dead (as I told you on the phone). It wont hold enough charge to start your car.
I can help you with it tomorrow.

Easy test. Do you have a voltmeter? If you dont have a volt meter, dont mess with it.

1. Check volts on battery

Should be 12v or more

2. Have someone crank engine while you check volts at battery

Should not drop very low. 9v is too low.

2a. How low did the volts drop?

3. If you can get it started, what volts are you reading at the battery?

It should be 13-14 volts at the battery if the alt is working. Dont worry, though. If you keep driving it without checking/replacing the battery like I told you, your alt will burn out form trying to charge a messed up battery and then you can replace that as well

GEEEZ doc, do you treat all of your patience this way??

I replaced the battery first thing this morning at Flaps. Volts are 12.5 with key off and jump up to 13.5 with the car running. so that should rule out the alt i think.

I believe in world peace

the lead off the battery splits at the battery, one heavy wire (starter mabey) and the other goes to a junction right next to the battery, at the junction there are at least 6 wires various guages going to alternator/ somewhere eles in the bay/ and lots of em go right into the cabin looks like it is not so easy to diagnose.

i also pulled the relays and got no change in the drain

"so i replace the battery with a new one"

Alright, my bad. I missed this part. No, I only treat you this bad

Do you have an ammeter function on your meter? If so, disconnect the red wore at the battery and place the meter in between the wire and battery. There should be close to 0mA (clock and radio draw). If you have a draw then you can start pulling fuses until you drop that draw. Find out what is on the circuit with the fuse and you have the culprit

I've changed a few engine wiring harnesses in these years/models before at the shop. The wire covering get quite hot, crack and then short(especially the EFi wires). I'd check there first. There are usually not fused-FYI

i dont yet have a book, where can i get a picture of some wire diagrams??

online it all seems like a scam,

i guess i will go to the bookstore tommorow