Battery not charging - ignition switch related? - Mercedes-Benz Forum
 
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post #1 of 6 (permalink) Old 04-11-2019, 09:14 AM Thread Starter
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Battery not charging - ignition switch related?

Before I begin, let me say that I have read several threads on non-charging problems, but I wanted to get some feedback on how best to diagnose this problem, given some pretty specific symptoms.

Background: I bought a cheap-ish '83 240D w/ 275K about a month ago - it had been sitting for over a year, but had a pretty good service history up through 2015. After replacing the battery and catching up on maintenance (oil change, front rotors & pads, tie rods) it was running fine for a couple of weeks until one morning when it barely cranked due to low battery voltage. Suspecting I might have just left an interior light on and drained the battery, I jumped it and drove 30+ miles but the alternator just wouldn't charging the battery. I drove it enough after replacing the battery to think that the alternator (which looked very old if not original) had probably just failed. I replaced the alternator with a 65 amp unit from AdvanceAuto, but it's still not charging.

As I said, I've read other related threads and have confirmed that the left-side dash lights (battery, brake, and pad wear warning) are all coming on when ignition is turned to position 2, so I'm pretty sure it's not the bad battery bulb problem described in some other threads. However, the pre-glow indicator light is working intermittently at best (more often not lighting now) even through I can hear the glow plug relay clicking off after ~15 seconds. The last time I got the pre-glow light to light up, it seemed to be sensitive to jiggling the ignition switch.
My questions:
1) Is the non-lighting pre-glow light likely caused by a bad ignition switch?
2) Can a bad ignition switch interfere with battery charging?
3) If yes to (2), any way to diagnose a bad ignition switch (aside from replacing the switch)?
4) If no to (2), what the hell is going on? Thoughts on other things to check?
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post #2 of 6 (permalink) Old 04-11-2019, 09:32 AM
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One thing to check are your cables. I had a bad ground cable that once replaced, solved my starting/dead battery issue. Replaced both positive and ground at the same time.

Good luck with tackling your issue.
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post #3 of 6 (permalink) Old 04-11-2019, 09:40 AM
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Maybe glow plug relay? Possibly the GPs are coming on and off and the alternator can’t keep up? Did you confirm the new alternator is good? Wouldn’t be the first time for one to be bad out of the box.


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post #4 of 6 (permalink) Old 04-11-2019, 09:50 AM Thread Starter
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Quote:
Originally Posted by victoriacoffeeroasters View Post
One thing to check are your cables. I had a bad ground cable that once replaced, solved my starting/dead battery issue. Replaced both positive and ground at the same time.

Good luck with tackling your issue.
Ground cable appears to be good - 0 ohm reading from negative terminal connector to any bare metal point on chassis.
Not sure how to check positive cable - would I do this by check continuity between positive terminal connector and the plug terminals for the alternator? If so, which of the 3 terminals on the alternator plug are relevant?
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post #5 of 6 (permalink) Old 04-11-2019, 09:55 AM Thread Starter
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Originally Posted by archham View Post
Maybe glow plug relay? Possibly the GPs are coming on and off and the alternator can’t keep up? Did you confirm the new alternator is good? Wouldn’t be the first time for one to be bad out of the box.
While I have not had the new alternator tested, I'm pretty sure that's not the problem. I've actually tried 3 alternators - the one install when I got the car, a spare that came with the car (trunk was full of spare parts, but most for other models) and the new one from AA.
Based on the clicks I hear from the GP relay it seems to be cycling on/off correctly with the ignition switch, even though the dash pre-glow light usually doesn't light up.
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post #6 of 6 (permalink) Old 04-13-2019, 09:48 AM Thread Starter
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Update on the non-charging problem:
So I decided to pull the instrument cluster to see if the non-lighting glow plug light was either burnt out or had a loose connection - neither true. With key in position 2 all the instrument cluster lights are lighting as they should except the GP light, but GP relay is working fine - verified that the voltage output from the relay is cycling as it should when the key is in #2 position, and I can hear the relay click on and then off after ~15 sec. While I had the cluster out, I verified continuity between the plug that connects the GP relay and the GP dash light.
I also inspected the radio wiring done by PO - messy, but nothing that appeared to interfere with the battery charging.
At this point I hadn't done anything that I thought would solve the problem, but for the hell of it I decided to put everything back together and try starting the car. GP light still intermittent (only lit once out of 5 tries), but now the battery is charging correctly (measuring ~14.5 v at the battery when running) regardless of whether the GP light cycles on!
MAYBE I fixed a loose connection when I removed/re-installed the instrument cluster, but I strongly suspect that the ignition switch has an intermittent fault. Only ~5 starts since the "fix", so I won't be surprised if the problem comes back again.

Quote:
Originally Posted by Cornell89 View Post
...I bought a cheap-ish '83 240D w/ 275K about a month ago ... it was running fine for a couple of weeks until one morning when it barely cranked due to low battery voltage. Suspecting I might have just left an interior light on and drained the battery, I jumped it and drove 30+ miles but the alternator just wouldn't charging the battery. I drove it enough after replacing the battery to think that the alternator (which looked very old if not original) had probably just failed. I replaced the alternator with a 65 amp unit from AdvanceAuto, but it's still not charging...
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