1985 300SD Battery Drain Caused by Starter? - PeachParts Mercedes-Benz Forum

mopart2 · #1 10-07-2011, 12:38 PM

Hello All,

I am new to this thread, but have owned some previous diesels (1985 300D). I just purchased a 1985 300SD with 200K on the odometer. The car had a dead battery when I purchased it, but has been very well taken care of.

It jump starts right up and when I put a charged battery in it will start right up.

I replaced the old battery with a brand new one and connected up a test light between the terminal and positive wire to search for a battery drain. Immediately the test light is lit up. I disconnected all the fuses first, then disconnected the alternator at the terminal block located on the passenger fender. Light is still lit up. I reinstalled the alternator power wire and then disconnected the starter power wire at the terminal block, the light went out.

I believe I have this traced back to the starter? The starter seems to crank over fine and is still actuated with the key.

Has anyone had a similar issue? (I have done some searching but it seems more common that the alternator is the problem)

Do you think this is a poor battery ground issue? OR should I just removed the starter and have it tested? Can the starter solenoid cause this?

Any help would be greatly appreciated.

Thanks.

TomAllen · #2 10-07-2011, 12:56 PM

Usually, there is not much in a solenoid that could leak. If it sticks the starte would continue to run after releasing the key switch.

Look to see if anything is connected to the other end (at the solenoid) of the wire you disconnected. If so, where does it go? A wiring diagram is a huge help here.

barry123400 · #3 10-07-2011, 01:05 PM

If their are no other power feeds from the starter then it's going to be the starter solinoid leaking to ground . Or current shunted up through the key circuit somehow perhaps.

For postitive proof disconnect the power feed to the starter and the small wire from the starter terminal. Take a wire from your positive terminal of the battery. Put your test lite in series with it. Touch the large terminal. You could actually use the battery feeder cable itself as the wire. Just try to not short it out if used.

If the light lights there is leakage. If not reconnect the small wire to the starter and do the test again. If it lights there is a constant drain somewhere through the key switch circuit. There may be simpler approaches to this but on the spur of the moment this is the approach I would use.

On cars where the large terminal of the starter is used as a distribution point with more than one wire on it the testing kind of would remain the same but there are more possibilities. Testing single feeder wire to the large starter terminal is easy and conclusive.

When you opened the connection at the jumping block on the front fender apron and the test light went out. I wondered if someone had wired an aftermarket sterio or amplifier in that may be constantly drawing. The power for that sterio would have been taken from the always hot side of the key switch. Something struck me as a little odd when you described that.

Still I am not working on cars as a steady diet. So some of my thoughts are suspect.

vstech · #4 10-07-2011, 01:21 PM

pretty common actually.
you can pull the starter much easier on an SD than a D, so you've got that going for you!
pull the starter, and open up the solenoid, there is a pictorial in the DIY section on starter rebuild with nice pictures.
clean off the contacts in the solenoid, and clean up the contact plate and bolts, grease everything up, and you should be good to go with the starter for another 100,000 miles.

mopart2 · #5 10-07-2011, 09:57 PM

First of all, thank you guys for all of your input and fast responses. I really appreciate it. Unfortunately, I have some more questions.....

I connected the light from the positive terminal to the large power terminal on the solenoid and no light. So i know the starter solenoid is not leaking. After multiple different wiring tracing scenarios, I figured out that the positive terminal goes directly to the starter and then another wire carrying 12v goes from the starter back to this terminal block on the passenger fender (which I unhooked yesterday). So by doing this i opened up every other circuit in the car besides the starter solenoid. So if you ever need to test the starter this is the easiest location to start testing from.

Next, I re-installed all wires and then started disconnecting circuits from the terminal block and found that the wire connected to the same post as the alternator wire (second terminal back starting from the front of the car). This wire runs up and underneath the battery? Does anyone know which wire this runs to? Is this the glow plug power? I am sorry that I do not have any wiring diagrams. I will try to get some pictures or something tomorrow.

If it is the glow plug relay power, where is the located? On the drivers fender? It looks like there are 3 other fuses or electrical junctions on the drivers side which connect to the glow plugs in some way.

carnut · #6 10-07-2011, 11:43 PM

Correct me if I'm wrong here but the postive cable to the starter should light up a test light. Its hot all the time waiting for the ignition switch to send power to the solenoid to switch the power to the start side of itself, thereby engaging the starter. Same with the positive feed wire at the back of the alternator. Hot at all times unless the battery is disconnected. At this point I dont believe you've verified a drain at all. The prior battery could have just failed. I would test the alternator output and unless the battery goes dead again not look for something that might not be there.

mopart2 · #7 10-08-2011, 08:27 AM

Carnut,

After re-thinking this overnight, I agree, I am just going to put the battery in the car and see if it goes bad. Thanks for everyone's input!