Lower wiring harness question

[FSK1460]

Hey guys, I'm trying to figure out where the lower wiring harness enters into the engine/firewall bay on my '94 E420? The wires going to the starter solenoid, alternator, and oil sensors have all finally deteriorated to the point the insulation has crumbled off and corroded them all.

I've had the upper harness replaced years ago and aware of the biodegradable insulation issue, but now discovered the starter solenoid wire is completely bare as well as the other wires for the sensors. I can see from underneath where the wiring harness goes up into a hole somewhere in the firewall, but can't seem to find where it comes out at.

If anyone has a picture or can describe exactly where the upper end of this harness connects to, that would be most helpful.

Thanks,

FSK1460
Tulsa, Oklahoma

 

[gsxr]

The wires at the top side connect to the terminal block behind the CAN box, and also to a rectangular-shaped multi-pin connector attached to the rear of the CAN box.

The wires go through a horizontal section of sheet metal on the .034 chassis, different than the .036 routing. On the top side it would be somewhere inboard of, and/or behind, the CAN box area. Might be some heater hoses blocking your view, but if you trace the wires from the terminal block behind the CAN box, you'll find where they go down the rabbit hole.

 

[FSK1460]

Thanks Dave for the quick reply. Looking at your fourth picture, is that thick blue cable with the black tape the one that goes to the starter?

 

[gerryvz]

Thanks Dave for the quick reply. Looking at your fourth picture, is that thick blue cable with the black tape the one that goes to the starter?

No, that appears to be an aftermarket power cable for the ICE (boom-boom stereo) system, which is connected to the + power position underhood.

Clear blue insulated cables werent invented yet back in the Dark Ages when these cars were new...

 

[FSK1460]

Yeah, I could tell that wasn't factory. Thought perhaps someone had rebuilt their own harness.

Any idea where the starter cable goes to up in the engine compartment? I can find the connector for the other wires behind the CAN box, but not sure where the starter wire is connected to. It's extremely tight up in there around the CAN box and below the wiper motor area against the firewall.

 

[gsxr]

Sorry, I should have clarified. The blue wire is aftermarket, feeding a fuse block for auxiliary electrical loads. But the large terminal where the blue wire connects, is the same terminal that the starter cable connects to. That is why I posted the photo. Just ignore the blue stuff.

Remember on the 034 harness, there is only 1 other cable bundle up top, all four smaller wires go to the rectangle connector that bolts to the rear of the CAN box. If you trace this (from the male pin side, NOT female socket side) you will find where it joins with the large wire that goes to the connector block + starter.

 

[FSK1460]

Ok that makes sense. Now that I know where they connect up to, I should be able to work my way back and pull them thru the unseen hidden hole in the firewall. Someone on another post mentioned tying a shoestring to the wires before yanking them down and then tying to the new harness and pulling back up is definitely a good idea.

Initially thought the starter Bendix gear was bad. Starter would spin but not engage. After a dozen cranks or so, it would finally take. However after reinstalling starter (with new Bendix gear), I then noticed the wiring to the solenoid was bare and corroded. The end of the solenoid wire was ok, but several inches further up is where the wires were toast. Don't think anything was actually wrong with the starter, just likely not getting enough current to fully engage solenoid.

I'll post some pics once I make some progress.

 

[LWB250]

The 034 lower harness is a pig to replace compared to the W140 with the M119. You'll need to drop or snake something (I used a straightened out coat hanger) to fish the new harness up and through the hole in the bottom of the false firewall behind the CAN box. It's tight, and definitely something that goes much better if you have a helper.

Rebuilding the harness itself isn't bad at all, whether it's for the 034 or the W140. It's mostly matching up wire sizes and judicious use of heat shrink, a crimping tool, and soldering iron. I always use silicone jacketed wire. It's more expensive and not always easy to find, but it's far more durable in the nasty environment that this bundle of copper has to exist in.

I just recalled something else - I keep high temperature split wire jacket (the woven stuff) on hand for repairs like this. Easy to use and assures that you'll keep the conductors away from those hot spots.

Good luck!

Dan

 

[FSK1460]

Thanks to you guys, I was able to locate the wire ends and get this out finally. It wasn't' as difficult I was thought it was going to be. Perhaps putting it back in may not be as fun. Having a lift in my garage made it much more bearable. Best tool ever!

After getting it out, it's amazing anything connected to it worked at all. Rubber insulated wires are not a new concept, they shouldn't self deteriorate like this. The starter cable is in good shape, just the four smaller wires that are shot. I'll work on running new ones, but may try that suggestion of silicone tape and see how that works.

 

[FSK1460]

Found the insulation in the four pin connector was totally disintegrated, all touching one another. Ran all new wires and used Silicone tape along with some wire mesh loom I had lying around. Turned out much better than I thought and wasn't too difficult to get installed back in. Tying a string to the original cable before removing is a must. Used two strings, one for the connector wire and one for the main lug wire then pulled them back up.

One issue I ran into during disassembly of the harness, was the oil level and the oil pressure sensor wires both broke. So I wasn't sure which one went where. Had a 50-50 shot and found they were backwards. The engine would start for a split second then shutoff. Since it ran before, I thought perhaps the ECU prevents engine from running if the oil level too low? So I switch the two pins in the connector up in the firewall and engine started right up.

Oil pressure gauge now showing full pressure and the starter turns over every try now. This fix was long over due.

 

[nocfn]

The rope method is a huge time saver.

 

[pablo2696]

Do any of you know where I can find the lower harness? I ordered from MBParts online and they cancelled my order because they are no longer available.

 

[gerryvz]

Do any of you know where I can find the lower harness? I ordered from MBParts online and they cancelled my order because they are no longer available.

Please contact our member @jhodg5ck. His shop rebuilds / remanufactures these harnesses.

 

[Gatorblue92]

Please contact our member @jhodg5ck. His shop rebuilds / remanufactures these harnesses.

Thanks for the tip on the harness. I've been on the lookout for one since my new E420 appears to have the original lower harness still and the oil pressure will occasionally dance between normal operation and zero.

 

[LWB250]

Thanks for the tip on the harness. I've been on the lookout for one since my new E420 appears to have the original lower harness still and the oil pressure will occasionally dance between normal operation and zero.

That's a very common indicator of a possibly failing lower harness. However, it could also be the oil pressure sender as well, as they have a tendency to fail as they age, tool. If you're covering both bases, be sure to only purchase the OE (VDO) sender, as aftermarket senders are notoriously unreliable.

Dan

 

[Gatorblue92]

That's a very common indicator of a possibly failing lower harness. However, it could also be the oil pressure sender as well, as they have a tendency to fail as they age, tool. If you're covering both bases, be sure to only purchase the OE (VDO) sender, as aftermarket senders are notoriously unreliable.

Dan

My money is on the harness. The PO replaced the sender in December right before I bought the car and I'm pretty sure the receipt said it was a VDO part.

 

[gsxr]

Do any of you know where I can find the lower harness? I ordered from MBParts online and they cancelled my order because they are no longer available.

Assuming you mean a 400E420 harness 124-540-31-30, yes, those are NLA from MB and the only option is to have Blue Ridge rebuild one for you (well worth it, btw). Which website allowed you to place an order? All the Revolution Parts dealer sites (Napervile, Husker, etc) are showing "Discontinued" (click here for example).

The E500E lower harness (124-540-27-30) should still be available.

 

[pablo2696]

Assuming you mean a 400E420 harness 124-540-31-30, yes, those are NLA from MB and the only option is to have Blue Ridge rebuild one for you (well worth it, btw). Which website allowed you to place an order? All the Revolution Parts dealer sites (Napervile, Husker, etc) are showing "Discontinued" (click here for example).

The E500E lower harness (124-540-27-30) should still be available.

I was trying to buy the 500E lower harness and for some reason the vendor told me they didn't have it anymore. Apparently it was a mistake because they contacted me and they do have it.

 

[gsxr]

Glad you were able to buy one. Which vendor was this, btw?

 

[pablo2696]

I used Mbpartshq

 

[S70/2]

The lower harness is so easy to rebuild I am surprised anyone buys new when mercedes already got ya once!

BTW as stated previously Tesa high temp engine bay cloth fabric electrical tape is available readily on amazon for under $5 a roll, all I use anymore

 

[gsxr]

I used Mbpartshq

Thanks! I was not aware of that dealer. They are the lowest-cost dealer I'm aware of currently, pricing is cost plus 15%, which is fantastic. Hopefully their shipping rates aren't terrible if you don't live close to Florida.

 

[pablo2696]

The total cost was $300.11 inclduing taxes and shipping to Miami. It was $263 + $17 (shipping) + $20 (taxes)... it wasn't that bad. Other dealers were a lot more expensive for the same product.

 

[pablo2696]

The lower harness is so easy to rebuild I am surprised anyone buys new when mercedes already got ya once!

BTW as stated previously Tesa high temp engine bay cloth fabric electrical tape is available readily on amazon for under $5 a roll, all I use anymore

I did my research and since I don't live in the USA (I live in Costa Rica), it is more expensive for me to send the harness to the US to have it rebuilt and then ship it back to Costa Rica than just buying a new one from the USA and ship it to Costa Rica

 

[S70/2]

I did my research and since I don't live in the USA (I live in Costa Rica), it is more expensive for me to send the harness to the US to have it rebuilt and then ship it back to Costa Rica than just buying a new one from the USA and ship it to Costa Rica

I get that but you could have rebuilt it for under $30 and about an hour of work with a soldering iron since all the connectors are reusable

 

[pablo2696]

I get that but you could have rebuilt it for under $30 and about an hour of work with a soldering iron since all the connectors are reusable

The connectors to the alternator, oil level sensor, and oil pressure sensor were either missing or broken. However, my upper engine harness still in good condition even though it is the original so I will try doing what you suggested to make sure it lasts for a couple more decades. Thanks !!

 

[gsxr]

There's an old thread on the forum with info on rebuilding the upper harness... note the upper has a LOT more wires, and in general is more complex / time consuming to rebuild. Those are still available new also, depending on which part number you need, should be $500-$600 or so if buying new.

 

[Duh_Vinci]

The wires at the top side connect to the terminal block behind the CAN box, and also to a rectangular-shaped multi-pin connector attached to the rear of the CAN box.
...

Dave, may I ask you for a little clarification (unless this needs to go to non-w124 related thread). Harness you have pictured, is very very similar to what my NLA harness would be on R129. I just want to understand what wire goes where (before I dive into the crumbling darkness)

Your harness (hope you don't mind the number doodling)



What my NLA harness supposedly looked like new



1: Main plug
2: Oil sender (to main plug 1, assuming I have a single pole unit}?
3: ??? (to main plug 1)?
4: Alternator (to main plug 1)?
5: Starter solenoid (to main plug 1, heavier gauge)?
6.1 and 6.2 Starter main cable (heaviest gauge)?



Regards,
D

 

[gsxr]

Here you go!

1: Main plug (On 124.034 only; 124.036 is different)​

2: Oil LEVEL sensor (to main plug 1)​

3: Oil PRESSURE sensor (to main plug 1)​

4: Alternator (to main plug 1)​

5: Starter solenoid (to main plug 1, heavier gauge)​

6.1 and 6.2 Starter main cable (heaviest gauge)​

 

[Duh_Vinci]

Here you go!

1: Main plug (On 124.034 only; 124.036 is different)​

2: Oil LEVEL sensor (to main plug 1)​

3: Oil PRESSURE sensor (to main plug 1)​

4: Alternator (to main plug 1)​

5: Starter solenoid (to main plug 1, heavier gauge)​

6.1 and 6.2 Starter main cable (heaviest gauge)​

I tried to study this harness from the broken corroded pictures on here and off the web, was a little challenging. Realized that there are two separate sets bunged into one loom...

Any chance you "may" have that plug 1 pinout (just in case if mine is beyond recognition)? I think I can guess the "Starter Solenoid" pin
Any other MB you know of may have the same square plug other than R129/M119 and 124.034 (hoping to just snag the connectors from the junk yard and bench build it before removing mine...

Many many thanks!

Regards,
D

 

[gsxr]

Best I can tell from the EPC, the rectangle connector is p/n A0185454328. If so, it's NLA. (!!!)

Appears to be only used on the R129, and W124.034? Great, another item to harvest from junkyard cars?

 

[LWB250]

Best I can tell from the EPC, the rectangle connector is p/n A0185454328. If so, it's NLA. (!!!)

Appears to be only used on the R129, and W124.034? Great, another item to harvest from junkyard cars?

View attachment 117301

I believe you're correct. The W140 used a round connector.

Dan

 

[gerryvz]

 

[Duh_Vinci]

Best I can tell from the EPC, the rectangle connector is p/n A0185454328. If so, it's NLA. (!!!)

Appears to be only used on the R129, and W124.034? Great, another item to harvest from junkyard cars?

View attachment 117301

Thanks Dave! And the list is growing? I rarely seen any W124.034 or R129 in the local yards...

I believe you're correct. The W140 used a round connector.

Dan

Yes, Dan, it is round, pulled up few parts from the search yesterday, that round one almost looks like O2 sensor plug on W140 harness...

Regards,
D

 

[LWB250]

Yes, Dan, it is round, pulled up few parts from the search yesterday, that round one almost looks like O2 sensor plug on W140 harness...

Regards,
D

It does resemble a O2 sensor connector, however, the lower harness connector has a few more pins in it....

Dan

 

[mikko.toivo]

The wires at the top side connect to the terminal block behind the CAN box, and also to a rectangular-shaped multi-pin connector attached to the rear of the CAN box.

The wires go through a horizontal section of sheet metal on the .034 chassis, different than the .036 routing. On the top side it would be somewhere inboard of, and/or behind, the CAN box area. Might be some heater hoses blocking your view, but if you trace the wires from the terminal block behind the CAN box, you'll find where they go down the rabbit hole.

Assuming you mean a 400E420 harness 124-540-31-30, yes, those are NLA from MB and the only option is to have Blue Ridge rebuild one for you (well worth it, btw). Which website allowed you to place an order? All the Revolution Parts dealer sites (Napervile, Husker, etc) are showing "Discontinued" (click here for example).

The E500E lower harness (124-540-27-30) should still be available.

For the European audience, you can refer to the following source [Kurth]: Mercedes positive cable harness A1245403130