My wiring harness bio-degraded and had to be replaced. Beside the starter and alternator it also connects to the oil pressure sensor and the oil level sensor. I ordered part number 1245403130 from my local dealer for $130. I could not find information on replacing this harness in the CD manual, nor on this forum, so here it is:

Removal:

1. Disconnect the negative battery terminal. Make sure it cannot accidentally touch the battery post by covering it with a small plastic bag.

2. Raise and support front of car and remove lower engine panel (cover).

3. Disconnect oil level sensor, oil pressure sensor, thick and thin alternator cables. Be sure not to lose any washers.

4. Turn steering wheel to left.

5. Remove pitman arm shield.

6. Remove starter shield.

7. Disconnect starter thin and thick electrical connections. To prevent breaking the Phillips screw on the thin terminal, I used a 1/4" ratchet wrench with Phillips tip and a long flat screwdriver to put pressure on the wrench while turning it. I guess Mercedes should have used a hex nut, not a screw here.

8. Under the hood, on the right passenger side, by the firewall, remove the square plastic cover of the power distribution block. Unbolt the large lug and thick cable. Locate the square connector at the end of the cable that branches from the thick cable, behind the box marked "battery in trunk". Disengage the spring clip of the connector with a screwdriver and pull out the connector.

9. Here is a trick that will save you time: Tie a long string on the lug. This will serve as a drag line for installation of the new cable.

10. Under the car, unbolt the two cable mounts still holding the harness, then pull it down and out. The old harness should be out with the drag line under the car. Untie the string.

Installation:

11. Tie the string to the new harness. Use electrical tape to cover the lug, the branch to the connector, and the connector itself. The drag line should go along with the branch, so you pull the connector first, then the lug. Have helper gently pull string from top, while you push harness up.

12. Guide other end of harness to alternator.

13. Connect thick cable at Starter.

14. Remove string and electrical tape, connect lug and plug.

15. The rest of installation should be in reverse order of removal. Use common sense and work safely!

This job took me 8 hours, but now I could do it again in 4. I had to find all connections and figure things out. Hopefully with these instructions somebody else can do it in 4 hours or less.

Attached Thumbnails

     

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1994 E420 139,000 miles

Thank You.

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'84 300SD sold
124.128

Great job. Thanks for the information and pictures. Out of curiosity, was it your starter, alternator or oil sensors that gave you the trouble before you decided to replace the lower harness?

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles? (broken odometer)

Thank you. It was the oil level sensor that gave me trouble. The insulation degraded and the wire rusted through and disconnected. See my earlier thread:

Oil Level Lamp is lit, but level is OK on 94 E420

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1994 E420 139,000 miles

This DIY is in the Wiki HERE.

Thanks!

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Bill Wood - Retired Webmaster
My Personal Website
1998 Mercedes E430
2010 Toyota Sequoia
My Photo Albums

Great Wiki! I just rebuilt my harness because I didn't have all of this great info here like a part number! It took me about a few hours since I brought my old harness into work, salvaged the connectors and resoldered the connections. I had a bad oil sensor, so I had a new spare one that the previous owner gave me with the car, and its bad! I will have to order a new one.

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1991 Mercedes Benz w201 190e 2.3 5sp.
1993 Mercedes Benz w124 300te 3.2 M104

For Sale:
2000 Mercedes Benz w210 e320 Wagon
$10,500---Sold!

Thank you; I'm glad you found it useful! I hope you saved some money over the dealer's $130 tag by making your own harness.

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1994 E420 139,000 miles

When I rewired my 94 e320 "B" Harness I only had to do the sensor wires because the battery cable itself was ok. Was the insulation good or bad on your battery cable?

PS Although the e320 L6 may not have the power of a V8, there's much more room to work and when not changing the battery cable, all the connections are on the engine's driver side.

It never occurred to me to repair the harness rather than replace it. I could not have repaired the wires while the harness was on the car because of lack of space. Judging from my photos the battery cable was OK, although you cannot see it from end-to-end.

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1994 E420 139,000 miles

The starter and alternator wires are bulletproof. It's only the 4 smaller wires that have a problem and they are very easy to rewire.