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Old 05-28-2007, 04:14 PM
lrg lrg is offline
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Location: San Francisco
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124 Idiot Light/Charging Issue

I have a wierd electrical problem with my 124 ('87 300DT w/187K miles) that I wasn't able to get help with in numerous searches.

When I turn the key to the on position none of the "minor" idiot lights goes on as usually happens at start-up. The ABS and SRS lights go on as normal (and off after 2-3 secs.) but all the other lights (all to the left) do not. The lights themselves seem to work normally. The high beam indicatior lights, the parking brake light, etc. work but none of them light at start-up. All the other instruments are working normally without any flickering or hesitation.

The second (and I'm sure related) problem is that my alternator is no longer charging at full power. The car runs just fine off the battery but it slowly goes dead if I don't recharge it overnight. The alternator was rebuilt about 12 months ago by a quality, specialist rebuilder and has been working fine until this light issue appeared.

Here's what I've done to check some possible problems:

Replaced the voltage regulator with a new, Bosch unit (the old looked fine by the way)

Cleaned contacts at alternator - all clean and all show +12V with ignition switch on and engine off. Good ground at alternator.

Checked belt for tension and condition and is A-OK

Removed battery (2 yrs. old), cleaned all grounds and had battery load tested. All good.

Removed instrument panel, checked all bulbs and cleaned all contacts with electrical cleaner and emory cloth - all good. No signs of burning or broken traces on the circuit board.

Applied power to terminals on pins at the back of instrument panel and got each to light

Checked all obvious grounds and other leads behind instrument panel - all looked good

Removed and replaced all fuses and ice cube relays at fusebox. Contacts all clean, fuses all good.

Removed and cleaned contacts at OVP - all looked good


I'm not sure what to try next. It's possible (although I think very remote) that the alternator itself has gone bad, however this doesn't explain the idiot lights. I've not done any work on the car in the last few months so this problem is new and couldn't have been caused by me bumping off a connection while doing another project. I have to believe the two problems (no idiot lights at startup and weak charging) are related. Any electrical wizzes out there that have any ideas?

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1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold
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Old 05-28-2007, 10:37 PM
babymog's Avatar
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Join Date: Jan 2006
Location: Northeast Indiana
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I'm not looking at the schematics, but it is possible that you have a bad ignition switch.

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