94 SL500 Lower wiring harness replacement - Mercedes-Benz Forum
 
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Old 03-09-2018, 03:53 PM Thread Starter
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94 SL500 Lower wiring harness replacement

Struggling with replacing the lower wiring harness on a '94 SL500. I have it disconnected from the ECU, Alternator, Oil pressure sending unit but I don't know how to access the starter to disconnect if there. very tight quarters. Do i need to disconnect the exhaust manifold to gain access from above or is there a way to access from below? Also does the harness attach to anything on the left side of the engine and if so what and where?
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Old 03-09-2018, 05:44 PM
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I have not done this yet, but will have to, upper harness is 2015 new, lower one is another story... I couldn't find any factory tech notes, if anyone has some info/pdf files, would be great!

For the time being, take a look at W140 forum DIY post on S500 replacement, should be helpful

https://www.benzworld.org/forums/w140...ml#post4809911

This one as supplemental as well https://www.benzworld.org/forums/r129...l#post13382177


Regards,
D
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Old 03-10-2018, 06:31 AM
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tight quarters is correct

Before you begin, turn your wheels hard left.......and then disconnect your battery

I just replaced this on my 95 sl 500. There is a bracket (bracket 2 in pic 1 upper left, also in pic 4) between the starter and the end of the "positive cable" (pic 2) where it connects in the transmission tunnel to the 12V stud.(pic 2) The bracket (pic 4)bolts to the trans bellhousing with an allen bolt. It can be difficult.


It is best accessed from above, between the firewall and the engine, using a 20" extension. After removing that bracket bolt, remove the two bolts that hold the starter to the bellhousing. This allows you to turn the starter downward so you can access the 12v and switch connections from the wiring harness to starter (pic 5). Remove the three heat shields that surround the starter. These are held on with sheet metal screws and nuts. Once this difficult part of the job is done and youve wrangled the heat shields off, you can tilt the entire starter, solenoid downward, and unbolt the 12v connection and the switched connection.

As far as having to remove the exhaust, it depends on your exhaust configuration. Sorry. If you can remove the drivers side pipe from the exhaust manifold to the left side pipe (my config) it will give you more room to work.

Good luck. dan
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Old 03-10-2018, 08:50 AM Thread Starter
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Thanks for the input. reviewed both the links and sent Buffalochip some questions. I'll update the forum as the project moves forward. FWIW the part number pelican parts shows for my harness is 129-540-05-30 ($340). Found it online at MB Direct for $240 and ordered it but have not received an order confirmation or shipping confirmation email so not sure what to make of that.
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Old 03-10-2018, 10:30 AM
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Make sure you have the correct harness part number for your VIN number. There's three different choices depending on the last six of the VIN. At those prices I would be tempted to rebuild the one that you have. It's a rather limited harness.
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Old 03-10-2018, 10:38 AM Thread Starter
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Thanks for the input. I'll check with the stealer for their take on the proper part number. Not opposed to paying for the right part but will rebuild if needed.
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Old 03-23-2018, 02:06 PM Thread Starter
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Ok the wiring harness is out, along with the starter and 3 heat shields. But before anybody starts on this job be aware that what is being called the lower wiring harness is actually 2 separate sets of wires that I will call A and B.

Set A is comprised of 4 18 gauge wires and 1 heavier wire that runs forward from which connect to the ECM. The 4 18 gauge wires run to the alternator, oil pressure sensor and the single pole unit beside the OPS and mine are blue, blue/red, green, red or brown. The heavier wire is purple/white and it goes to the starter solenoid. The only wires in my case that failed were the 4 18 gauge wires which can easily be replaced without removing the starter, heat shields, etc.

Set B is really a single 6 gauge wire that runs from the firewall connection with the main battery cable to the starter and on to the alternator. In my case the insulation on this wire did not fail and shows no signs of wear.

THIS MEANS THAT I DID NOT NEED TO REMOVE THE STARTER AND THE BLASTED HEAT SHIELDS TO RESOLVE THIS ISSUE.

I was fooled because there was excess of the 4 18 gauge wires that was taped along the purple/white solenoid wire and which disappeared behind the exhaust header in the direction of the starter. Pulling on these wires did not dislodge them so I assumed that they were part of the "lower wiring harness". In the picture you can see the round rubber wrap that the P/W wire continues through while the 18 gauge wires are folded back.

I am off to Lowe's to buy some 18 gauge stranded wire that is heat and petroleum resistant for $8 for 35'.
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Old 03-23-2018, 03:03 PM Thread Starter
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And another picture which clearly shows the cables A & B along with the starter.
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