W124 300E-24 Relay Types and Location

jonclancy

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I was recently fettling the electrics on my newly acquired W124 300E-24 and thought that sharing might help someone else out. I had to do a bit of googling to find some of this info, and there are still a couple of questions I have yet to answer.

This is a useful document:

http://johnmeister.com/DieselBenz/TECH/Overvoltage-Relay/relay_control.pdf

Having checked the continental fuses in the fusebox (engine bay, offside near bulkhead - part no 124 545 01 40), I found all were oxidised, though the fuse-holders looked brand new. I replaced all the fuses (see owners' manual for ratings; a bag of 200 various fuses was bought from Amazon for a few quid). I also used Contralube 770 on all the fuse ends to keep any future oxidisation at bay.

This done, I removed the fusebox screws to reveal the relay box behind. Each relay was pulled (apart from the N7 Hella Exterior Lamp Failure Monitoring Unit 126 542 03 32 in position "K") and the pins, which all looked brand new, were lubricated and the relays replaced.

One relay in location "F" had a small fusebox with a single 25A blue fuse fitted - though the electrical connection was not made as the second fuseholder was empty. I cleaned up the connectors and lubed/replaced the fuse. Googling seems to suggest that this fuse/relay is something to do with having a trailer/towbar fitted, but I'd be interested to hear if there are any other suggestions, please.

Relay Positions, Function and Part numbers from the linked doc and photos from my car:

A = K5 Power seat relay module - This is a convenience relay in my car (0015427819)

B = K9k1 Auxiliary fan relay Models 124.034/.036
K10 Auxiliary fan preresistor relay module - This is SR9850 relay in my car.

C = K9 Auxiliary fan relay module
K9k2 Auxiliary fan preresistor relay Models 124.034/.036 - This is Multi-Purpose Relay Siemens 899865 in my car

D = K2 Headlamp washer relay module - 126 820 20 26

E = F14 Auxiliary fuse holder (ATA)
K17 Secondary air injection relay module
Models 124.034/.036 - This is SR9850 relay in my car.

F = K24 Convenience relay module - This is Aux Fuse Holder in my car.

G = K18/1 Seat belt warning relay module (Coupé only)
K29/1 First gear start relay module - Not fitted in my car.

H = N10 Combination relay (turn/hazard signal, Heated rear window, Wiper motor) - 201 821 00 47

I = V5 Disconnect diode (parking brake/ASR/electronic accelerator)
Models 124.034/.036 - Not fitted in my car.

J = OMITTED

K = N7 Exterior lamp failure monitoring module 126 542 03 32
 
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jonclancy

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Fusebox
 

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jonclancy

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Relay Locations
 

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jonclancy

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Position A

Convenience Relay
 

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jonclancy

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Position B

SR9850 Relay
 

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jonclancy

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Position C

Multi-Purpose Relay Siemens 899865
 

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jonclancy

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Position D

Headlamp washer relay module - 126 820 20 26
 

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jonclancy

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Position E

SR9850 Relay
 

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jonclancy

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Position H

Combination relay (turn/hazard signal, Heated rear window, Wiper motor) - 201 821 00 47
 

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kth286

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Your Mercedes
E320 Coupe 95
I like the attention to detail.
 
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johnney

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Thank Jon

This is excellent

Do you know if it is possible to repair a Relay

Can the contacts be accessed and cleaned ?

Thanks
John
 

Miffy

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Your Mercedes
CLK 320 CAB Elegance C208
Thank Jon

This is excellent

Do you know if it is possible to repair a Relay

Can the contacts be accessed and cleaned ?

Thanks
John

A few have opened them up and re-soldered bad joints etc so why not give it a go
 

television

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Your Mercedes
2002 SL500, 216 CL500, all fully loaded
Thank Jon

This is excellent

Do you know if it is possible to repair a Relay

Can the contacts be accessed and cleaned ?

Thanks
John

Mercedes relays when fitted to a PCB can get bad soldering after some years.
The constant open and closing breaks away the solder. using a good cored solder, not lead free heat up each joint on the relay and apply new solder and when the joint is bright and shiny it should be just fine.

Using a jewelers magnifying glass the defects can be seen as a black circle around the joint.
 
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jonclancy

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BTW, as TV says above, do not use unleaded solder. Use either 60/40 lead/tin rosin cored, or a low melt leaded.

Seearch eBay for Multicore LEADED 60/40 solder - I found 1.5m for £1.39 delivered.
 
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