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:
Disconnect the negative battery terminal. Make sure it cannot accidentally touch the battery post by covering it with a small plastic bag.
Raise and support front of car and remove lower engine panel (cover).
Disconnect oil level sensor, oil pressure sensor, thick and thin alternator cables. Be sure not to lose any washers.
Turn steering wheel to left.
Remove pitman arm shield.
Remove starter shield.
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.
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.
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.
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.
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.
Guide other end of harness to alternator.
Connect thick cable at Starter.
Remove string and electrical tape, connect lug and plug.
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.
Discuss this DIY here.