1985 300sd w126 not charging at the battery - Page 2 - PeachParts Mercedes-Benz Forum

rwd4evr · #16 06-25-2019, 11:00 PM

https://youtu.be/C-YqwzWQxwU

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rwd4evr · #17 06-26-2019, 12:15 AM

I hooked the field to positive while running and got it to start charging. The jumper started to get warm so I dissconnected it and it kept charging. I checked the light and it was out. By the time I got back to the meter it was not any more. Now it will charge from the field wire but it gets warm quick so I'm not trying to roast anything else. I tried running the alt output direct to battery positive and it does jack ****. This makes no sense.
On a side note I put power to the purple wire that is the starter solenoid key wire by accident when I jumped the starter and I could hear the abs module clicking. Dissconnected that to get it out of the equation to no avail.

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rwd4evr · #18 06-26-2019, 02:01 AM

Can another 300sd owner check for the odd reversed ground on their car? It's something to do with the glow plugs system. Must be a diode in there or some thing. Just check for power with a meter with negative on the left terminal on the block down on the frame rail by the alt. And positive on the + battery post.

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oldsinner111 · #19 06-26-2019, 06:43 AM

if I may interject, on most cars,engine ground straps are either old,or not very good.I always add one from negative battery terminal to engine block.It helps charging rate.

rwd4evr · #20 06-26-2019, 11:30 AM

I tried running a jumper cable from the negative right to the alt mount and it made no difference. Voltage readings are the same anywhere it's tested.

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rwd4evr · #21 06-26-2019, 06:41 PM

All that fighting to find it was the damn replacement spade connectors on the alt done by the PO. I looked at them and even wrapped some tape to make sure they aren't touching before I knew they went to the same place. I got it charging with my own bat/field light intermittent and was feeling around and noticed the were pretty hot. Stole the harness off a junk w201 here and boom. Fixed. 13.5 isn't exactly record numbers but I'll see how it balances out after driving a bit. I know how to do an upgrade to a more modern r129/w124 alt now anyway! Thanks for any thoughts on the subject!

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optimusprime · #22 06-27-2019, 05:47 AM

It all looks poor, just looking at the pictures i would be worried if my set up looked like that in the picture .

rwd4evr · #23 06-28-2019, 01:28 AM

Yeah it did look sh++y. I cleaned it all up and robbed a junction off the w201 too since the original wires wouldn't reach and the screw was stripped. 3 hour trip today towing a small trailer went well except for water in the fuel. Had to stop and dump the filter a couple times.

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unavita · #24 10-02-2022, 11:33 PM

Quote:

Originally Posted by Diseasel300

The alternator/chassis wire is on the POSITIVE side of the battery, not the negative. The heavy positive cable goes to the starter, the pigtail goes to the 3 post terminal on the false firewall and thus out to the chassis and alternator. Pull up the ETM on Startek and it'll make it clear how the wiring should connect. The fact you have 14.4 on the field wire says the alternator works, power just isn't making the trip to the battery.

Does anyone have a jpeg or pic of this?

I'm getting all kinds of gremlins and trying to chase it down like the op. My false firewall connection (will post pic tomorrow) was rebuilt. It is getting 14.1 and one post and 13.9 at two other posts.