Hi yall i have a 1991 300D 2.5 Turbo w124 with a strange electrical problem>>>
The battery is not being charged and its a brand new battery also it is a brand new alternator,,
---They both test well separately outside the car at test bench.
when put in the car the battery is not being charged if you do an alternator check with a tester sold at the local auto shop as the car is running the test says alternator voltage BAD if you press on the gas pedal it starts saying alternator voltage GOOD!!!!
---I replaced the OVP overload protection relay a while back when the tachometer and AC was not working and it was not charging and that solved the issue. So when it started doing this i changed the ovp again and boom it was charging the battery but no AC and reverse lights!!!!
---So i went and returned that ovp got another one thinking that it was just bad luck now the new symptoms are the one expressed above everything works ac and lights and tach but no charging of the battery i must say that when you have the AC at full fan speed the ABS light will sometimes come on as the car idles and go away when you press on the gas, tach works fine etc.
What can it be and how can i trouble shoot it further more?? cause its tiresome to get out and jump start the car with a portable jumper everyday in the trunk
any help will be greatly appreciated
thanks
Denis

I just got done fixing my OVP in my TE. Turns out it was full of water.. I have read that one of the symptoms is a dead batt. My check engine light was coming on with the car off and key out, then started "clicking" while off. Anyway, you may want to look into that.

BTW: after taking my OVP apart and fixing it, I put a ziplock over it so it will not fill with water again.

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08 R320 CDI current

Past
95 E420
87 300D Turbo 5spd
90 300TE
83 300SD
85 300TD
92 400E
85 190D

Hello Denis,
Did you check the 10 amp fuse on the OVP relay?

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92 300D 2.5L OM602 OBK #59

Yes i did check the 10amp fuses they are fine but i still replaced them.
I took the car at the battery shop right now and for some odd reason it said BAD battery and its a new one so i will be changing it and see whats up maybe recharging the battery so may times with the portable charger fried it
will let you know what i find
Denis

You need to check the connections on the back of the alt. The thick wires often go bad.
The earth strap from the body to the motor needs to be removed & the surfaces it connects to cleaned.
Is the idiot light glowing when you turn the ignition on? Does it come on ever?
The OVP relay is not a part of the charging system. Probably the issues with the OVP relay are similar to the problem you have with the charging circuit ~ bad connections. Why would I suggest this ? Had this problem on 2 cars in the past. On one, ended up installing a thick wire direct from the back of the alt to the battery & a thick earth from the alt casing to the battery.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I see that this was posted a while ago but I'm having pretty much the same issue with my '84 300D. My alternator and battery are brand new, and it was working for like two weeks until it acted up and only worked occasionally. (oh and no idiot lights) My theories are: bad alt wires (might've gotten a little cooked), bad relay, bad "field activator thingy" (quoting what someone said on another forum) etc. Might I ask, where exactly is the OVP? I have yet to find it to check it. And did you resolve your problem?

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Matt.