'83 300SD - dead short across the battery. - Page 2 - PeachParts Mercedes-Benz Forum

kerry · #16 10-05-2009, 04:37 PM

Quote:

Originally Posted by destroy

I have a short across my battery cables on the car when they're unhooked from the battery terminals

What do you mean by that? Are you saying that when you connect the two cables with an ohmmeter that you are not getting infinite resistance? All that would mean is that some circuit is closed.

briporte · #17 10-05-2009, 04:52 PM

How you described your trip home reminds me of my own experience with a voltage regulator. Yours could be at the end of its brush life. This happened to me. Zero voltage at the battery when the car is running and normal voltage at the battery when the car is off. If driving at night, your headlights and accessories will drain the battery down while driving...and everything goes dim, dimmer, dead. None of your electrical will work, but the car will remain running. The battery is not required for the engine to run, just to start. Thats why a jump start works so well. Thats my nickles worth.

turbobenz · #18 10-05-2009, 05:00 PM

I had a similar problem also. It was a loose ground strap interrupting the charge circuit. I would go for a drive and everything would get dim and die, and then id hit a bump and theyd all come back to life for a second

destroy · #19 10-05-2009, 05:20 PM

Quote:

Originally Posted by kerry

What do you mean by that? Are you saying that when you connect the two cables with an ohmmeter that you are not getting infinite resistance? All that would mean is that some circuit is closed.

I used a process of elimination to try and find out exactly where the short is.

The first thing I did was remove the battery from the car. I put my ohmeter on the continuity setting and found the positive and negative cables from the car were linked. I've cleaned all terminals and connectors including where the battery cable is grounded to the car. We tested the resistance on all of the wires as well, and the only suspicious thing came when I jiggled the key in the ignition as I said before.

ah-kay · #20 10-05-2009, 05:47 PM

I really cannot follow your logic or diagnosis. If there is a 'Dead Short' then the battery cables would have been fried by now. We are talking of massive current and heat flowing through. No battery cable can take that kind of current.

So you do NOT have a dead short.

What I suspect the alternator is over-charging the battery and kill your new battery. Or the regulator is faulty. I would suggest to proceed as follows:

1) Get a reasonably good shape battery, new or old.
2) Disconnect the alternator wire from the alternator, i.e. it will spin but will not charge the battery. Or remove the belt, whatever is simpler.
3) Run the car and see everything works as expected. The battery will run down but it will take a long while.
4) This will eliminate a lot of possibilities. If it runs fine then the problem is the alternator.
5) If not then it is possible that there is a wiring short somewhere. Then you need to do elimination by removing the fuses. Check the fuse rating but if you have a short then some fuses would blow. That is what they are for.

Good luck.

destroy · #21 10-13-2009, 08:06 PM

Update:

Pardon my poor terminology here. I'm still a young buck and although I'm learning fast, I've only really started doing any of my own work on any of my vehicles in the past couple of years or so. My dad's helping me a bit with this, but there's been no time in the past week for either of us to do anything.

Today I pulled out the instrument cluster and I now have access to the wiring harness on the back of the key cylinder. When he gets the time in a couple of days to help me (can't test with only two hands) we'll see exactly what's going on. I talked to him about it and he says it wasn't actually a dead short after all, but the resistance we were getting was around 1 ohm, so it was definitely sucking the battery dry and that no doubt caused it to boil.

Voltage regulators are cheap so I'm going to order one and throw it in anyways, we'll see if that helps. Will update in a few days when the next progress arrives.

Thanks again.

destroy · #22 10-17-2009, 09:00 PM

So I've done a bunch more testing and have had some varied results.

From what I remember there's no current draw when the car is off and the key is out. We've got a special inductive meter that will measure current so we tested that way. I'm pretty much positive I need a new voltage regulator, as the battery isn't being charged currently. That much is decided on.

However, with everything now hooked up I'm finding that the car simply won't turn over with the key. As far as I can tell, everything is wired up correctly. We got it to fire up by jumping the starter with the key in the on position. When we do this, the starter stays engaged after the engine is running.

Still, I'd like to get the key to do the work. I've taken the harness off of the back of the tumbler, taken it apart, and put it back together multiple times. We've looked at the wiring diagrams to try and find out if it was put back together wrong, but no matter what we do the key won't activate the starter.

Is it worth trying to just put in a new ignition? Any ideas?

NoSparkNeeded · #23 10-17-2009, 09:08 PM

I had several strange electrical random problems when I first purchased
my TD. Reading here convinced me to just change out ALL the fuses.
It didn't exactly make logical sense to me, as I checked each and every
fuse with good Fluke meter, but sure as heck, I removed and tossed all the fuses, carefully cleaned all the connections with WD40 and a little piece of #600 paper, replaced all the fuses, and everything has been perfect. I carefully checked everything beforehand, but just replacing the fuses for like, 10 bucks, and ALL my gremlins got scared and left

.

compress ignite · #24 10-18-2009, 02:55 AM

Then I'd REPLACE the Electrical portion of the Ignition Switch.

Too much of your diagnostic symptomology points to a BAD ignition switch.
(I.E. "Jiggling the Key","Wires connected to the Ignition Switch that cannot be
empirically tested")..AND HERE"S THE KICKER: the RETURN spring on the Switch
doesn't return the KEY to position #1 after starting...........WHOA!
A bad BENDIX on the STARTER will exhibit the same "Hangup".Check the Starter.

destroy · #25 10-28-2009, 09:06 PM

We've been working at this on and off for a while now and have made a little bit of progress. I bought a used alternator off a guy parting out a car, and had both of them tested. The one I bought was in a bit better shape so we went with that one, so the alternator is taken care of.

We did some more fiddling around with it last night. Today after studying the wiring diagram I took apart the connector to the back of the ignition switch and made absolute sure that all of the wires were going to the right pins. I ordered a new ignition switch on Monday and got it yesterday, so I tried just plugging the connector in and turning the back of the switch with a screwdriver. I also tried running the shifter all the way from park down to low and no luck.

At this point we're thinking it might have to do with the starter lockout switch. Is this related to or the same as the neutral safety switch? I've been doing some searches and I'm getting similar symptoms. Even though I've neglected to say bring it up out of embarrassment for my stupidity, I should mention that shortly before the trouble started I did spin the tires pretty good on the gravel... you know, young men and all...

kerry · #26 10-28-2009, 09:59 PM

It could be the neutral safety switch. Do a search on jumping the neutral safety switch or nss, and you will find instructions on how to jump the wires near the accelerator.

Codifex Maximus · #27 10-28-2009, 10:24 PM

Things I'd check if it were me: ( brain dump warning

)

Disconnect battery cables, measure voltage across battery terminals; should be 12+ VDC measured with a multimeter. If you can check the cells, make sure they are topped off to puckering with distilled water. Try to charge the battery with a trickle charger. If it wont hold a charge, replace the battery.

Clean the battery terminals with baking soda and water if they are corroded. A special wire brush/terminal cleaner helps too. Don't overdo the cleaning as you can lose material from the posts/terminals.

Reconnect battery cables and start the car if possible. If not enough charge then try to jump it and get it started. Measure voltage across the connected battery terminals. Should be at least 13+ VDC preferably up to 15VDC while charging.

Anything less than 13VDC indicates a charging circuit problem. (I believe the alternator puts out at least that much even when the battery is fully charged?) That pretty much means alternator, rectifier, voltage regulator and wiring need to be checked.

Check alternator wiring for problems and make sure those belts are tight and not cracking or frayed.

If, after connecting the battery terminals, you measure the voltage across the battery and it dips below 12VDC, you can safely assume a short somewhere. Also, if after you turn the key to the glow position the voltage drops below 12VDC, there probably is some kind of short. And especially, if the voltage drops while the car is running. Shorts typically have less than 10 Ohm resistance. You can calculate current based on voltage and resistance. DC current = VDC / Resistance in Ohms. C=V/R Compare calculated current to measured current from your inductive meter. There usually are devices in your car which pull a few milliamps when the car is off. Example: If you measure 1 Ohm resistance across the battery terminals and you have 12VDC across the battery, then with the battery terminals connected you would have a 12AMP draw given stable resistance after connecting the battery. Too much current draw and the battery voltage would drop. Power = V * A giving you 144Watts. Not sure how many watts that clock pulls... heh

If you think there is a short, the fuse procedure, as previously suggested, where you go through them one by one, is a good diagnostic method. (how's that for a double appositive phrase sentence?) Your fusebox has listed fuse values in AMPS. Do NOT use a higher amperage fuse than is designed for the particular fuse slot; this can cause wires to burn and short as well as damage to components. If you replace a fuse in a slot and it burns out right away - you have found a problem in that circuit.

Getting into that dash is no fun the first time and undoubtedly the second. If you're going to go in there then best to do a good thorough check of most under-dash components. I'm currently doing this with one of my cars. Learned alot thanks to the other folks on this board.

I've not had to change an ignition switch yet so no advice on that one. Just some basic electrical knowledge I've gleaned over the years.

Sorry for rambling... hope this helps in some way

Codifex
1981 240D SkyBlue (needs an engine)
1983 300DTurbo w/sunroof

destroy · #28 11-09-2009, 08:00 PM

I fixed the beast last Tuesday. Skeptics be damned! Even with the help of two smart old men (one of which owns and works on his own '80 300SD), it took my tenacity to keep at it.

I ended up buying a new ignition switch that I didn't need (anyone need a new one? hah), but also picked up a used alternator from a guy parting out an old 300. Ad said it was an '86 but it was definitely a non-turbo... had both the one from my car and this one tested, went with the bought one since it was slightly better and took the pulley from mine. I think the alternator was what fried the old battery, for some particular reason.

In the end, the wiring on the junction from the battery/starter/alternator etc was wrong. The smaller white guy was on #3 instead of #4. I was fairly confident I had put it together correctly, but wasn't sure. That picture of the remote starter on here tipped me off and she fired right away. So good to have her back!

Now that I've just bought myself a nice Ford Powerstroke van for a steal with a ton of electrical problems I'm just getting started! I figured out a few quirky things in the electrical systems on these things. One thing I've learned about electrical systems and will have to remember when fixing things in the future: K E E P I T S I M P L E, S T U P I D!

I'm planning on doing some searches and reading tonight to figure out the rest. Onto the next with this guy:

#1: My heater is only working intermittently. Sometimes it's just regular chilly outside air, sometimes I get the heat. I can always get air, but it's primarily through the defrosters and the far sides of the dash vents. Is this the mono switchover valve? My coolant never really reads much above 40 no matter how hard I drive it and it only ever really reached 80 during the tough summer days. I tested it and it appears to be in decent shape, but I'm planning on changing my coolant and thermostat anyway since the car sat for a while before I bought it. I imagine this can't hurt? Anyone know where to get the right coolant at Canadian retailers?

#2: On Friday when driving the new van home, my friend was driving my car and he noticed my fuel gauge stop reading completely. I'm planning on pulling the cluster and checking the connections because that could be it, but I'm curious if there's a trouble spot. The needle was jumping all over the place on the way home today. I've been running B5 for a couple of tanks now. Could that have anything to do with it?

Thanks again.

-Sean

Codifex Maximus · #29 11-09-2009, 09:46 PM

Quote:

Originally Posted by destroy

#2: On Friday when driving the new van home, my friend was driving my car and he noticed my fuel gauge stop reading completely. I'm planning on pulling the cluster and checking the connections because that could be it, but I'm curious if there's a trouble spot. The needle was jumping all over the place on the way home today. I've been running B5 for a couple of tanks now. Could that have anything to do with it?

I don't know if I'd go pulling the IC just yet. There have been more than a few people having issues with a jumpy fuel guage; it's usually caused by issues with the sending unit at the tank. My 240D does this.

Do a search.

Anyway, here's a link that may help.
80s Mercedes - how common are "dancing" gauges and other 80s MB questions...

Codifex
1981 240D ChinaBlue (found an engine - hope it's good)
1983 300DTurbo w/sunroof

Shawn T. W. · #30 11-09-2009, 09:57 PM

Quote:

Originally Posted by destroy

I fixed the beast last Tuesday. Skeptics be damned! Even with the help of two smart old men (one of which owns and works on his own '80 300SD), it took my tenacity to keep at it.

I ended up buying a new ignition switch that I didn't need (anyone need a new one? hah), but also picked up a used alternator from a guy parting out an old 300. Ad said it was an '86 but it was definitely a non-turbo... had both the one from my car and this one tested, went with the bought one since it was slightly better and took the pulley from mine. I think the alternator was what fried the old battery, for some particular reason.

In the end, the wiring on the junction from the battery/starter/alternator etc was wrong. The smaller white guy was on #3 instead of #4. I was fairly confident I had put it together correctly, but wasn't sure. That picture of the remote starter on here tipped me off and she fired right away. So good to have her back!

Now that I've just bought myself a nice Ford Powerstroke van for a steal with a ton of electrical problems I'm just getting started! I figured out a few quirky things in the electrical systems on these things. One thing I've learned about electrical systems and will have to remember when fixing things in the future: K E E P I T S I M P L E, S T U P I D!

I'm planning on doing some searches and reading tonight to figure out the rest. Onto the next with this guy:

#1: My heater is only working intermittently. Sometimes it's just regular chilly outside air, sometimes I get the heat. I can always get air, but it's primarily through the defrosters and the far sides of the dash vents. Is this the mono switchover valve? My coolant never really reads much above 40 no matter how hard I drive it and it only ever really reached 80 during the tough summer days. I tested it and it appears to be in decent shape, but I'm planning on changing my coolant and thermostat anyway since the car sat for a while before I bought it. I imagine this can't hurt? Anyone know where to get the right coolant at Canadian retailers?

#2: On Friday when driving the new van home, my friend was driving my car and he noticed my fuel gauge stop reading completely. I'm planning on pulling the cluster and checking the connections because that could be it, but I'm curious if there's a trouble spot. The needle was jumping all over the place on the way home today. I've been running B5 for a couple of tanks now. Could that have anything to do with it?

Thanks again.

-Sean

#1 sounds like either a stuck open (or broke like mine!) thermostat, or none at all! Not sure about where to get "proper coolant" up there (I bought mine at Napa) but the dealer should have some!

#2 sounds like a ground problem . . .