Starter & Alternator Harness Replacement on 1994 E420
 

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.

Nice Job!
 

Thank You.

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?

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:

http://www.peachparts.com/shopforum/tech-help/246379-oil-level-lamp-lit-but-level-ok-94-e420.html

It's in the Wiki
 

This DIY is in the Wiki HERE.

Thanks!

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.

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.

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.

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.

I have the same problem mine was discharging the battery then I found the crumbling wires. I am waiting for harness to come in, thank you for this detailed post. It has really helped me fix my beautiful car. :)

You're quite welcome. It is amazing to me how something I barely remember writing over 7 years ago keeps on helping people.

I am unable to remove bracket nearest starter it is also part of transmission dip stick bracket, the top most mount is unreachable, The nut on the shared bracket was a monster to get loose. 17mm had to use breaker bar. I am about ready to destroy bracket to get grommets out of it. every other part is done and ready to come out. Did any one else run into this issue mine is 1995 E420. The harness is no longer available I will have to run new wires and solder them to connectors. The tip of using ratcheting wrench with Phillips worked perfectly :)

I have decided to cut the harness bracket, so as to remove harness and leave bracket attached to transmission fill tube bracket. It seems to me the harness bracket should have been over tube bracket so as to have it the easiest to remove, so one must have worked on this before and switched brackets position. Also it seems to me to be over engineered, the harness bracket could serve best as a holder that is a 200 degree circle and not full so as to make removal in installing simpler yet maintaining its intended purpose

Job done
 

:D Cut bracket got harness free, restored harness new wires and solder connections. Recovered in rubber hose, did the string thing :) and had my daughter help me fish harness up to the top look for channel it feeds through, just above where bracket farthest from starter is. reconnected all and started and drove. Very pleased. Thanks again for this detailed post. Just a word about you will need 10mm, 13mm, 14mm, 17mm sockets with extensions and universal . all else is just patience and persistence.