W126 Relay Identification
 

1990 300SEL

Having startup issues and in another thread someone suggested checking/changing certain relays and a few nice people tried to help but "weren't sure' so I want to throw it open to all the smart people everywhere on this forum!
I am attaching 4 pictures with possible relays circled in blue in hopes that someone can identify the relays.

Thank you for any help.

In the 1st picture the black plastic holder is the blower fuse.

In the second picture that is the engine/chassis harness connector.

In the 3rd picture the relay with the knob is the MAS relay.
And the relay with the fuse is the over-voltage relay.


In the 4th picture you have the ABS control module connector,
and the diagnostic connector.

Thank you very much!

In Picture 1, could you please tell me what the circled silver part on the right is? It looks like a relay but I don't know what it is.

In Picture 4, is the diagnostic connector the circled one on the left?

Because of hard starting, a forum member said it is often due to improper functioning of the "fuel pump relay and the overvoltage relay. these are in a row with the Klima relay". You have told me where the overvoltage relay is, but I don't see any other relays there "in a row" and therefore don't know where the fuel pump relay (or Klima relay) is - can you help me find the fuel pump relay?

Again, thank you.

fuel pump & klima relays were merged in 1990 into the MAS relay.

4) Yes

Thank you so much for helping me.

The only thing not resolved is the silver (relay, I think) circled on the right in Picture 1 - do you know what that is?

That is the up-shift delay relay (K29).

Yea! All done, thank you so very much.

The MAS relay Pin # 1 And #2 control the fuel pump relay .
Combining them has reduced the "row 'but its still there .
mak

So if someone on this forum told me hard starting frequently requires replacing the fuel pump relay, and there is none, where do Pins 1 and 2 go, how do I identify pin 1, and is there something I can take apart and clean or renew to be sure it's not the fuel pump relay causing trouble?

It seems You did not follow MB doc's explanation above , instead of a separate fuel pump relay and a separate KLima relay , the 1990 model has combined them together as a single MAS relay. which functions as a fuel pump relay + AC relay.

when you remove the MAS relay , the Pin#' s will be written on the underside near the pins .
Initially just clean the pins and sockets and hopefully this Will sort the erratic running problems the car has .
Pins 1 and 2 bridged togather run the fuel pump directly without the MAS relay.
If you intend to replace for utter relability then its the MAS relay,all age related faults in the 103
Good luck!!
mak

Drosen, if the fuel pump relay is bad, it will manifest itself by not turning on the pump when you turn the ignition key. This can be easily checked by opening the door, and listening for the hiss of the fuel pump from the rear of the car when you turn the ignition key on (or have a friend stand behind the car and listen for it).
Each time you turn the key on the pump will run for 2-3 seconds, then turn off. So, to check it, just turn the key on and off a few times and listen for the hiss. The pump is located just right of the fuel tank, and makes a very audible noise in a quiet garage - even a deaf old guy like me can hear it from the driver's seat.
To also do a rough check of the fuel pump output, the accumulator, filter, and the residual pressure of the system; you can try turning tthe key on/off 2-3 times before starting the engine. This will run the pump 2-3 seconds on each key turn, and prime the system. If this fixes your starting problem, then you know where to look further at the items I listed above.

DG

Sorry for the delay,to everyone who has been kind enough to be helping me, I got called out of town for work. Back now.

mak: Thank you - I know how to clean the pins, but how does one clean the sockets? I don't have anything small enough to get in those little holes!

S-Class Guru: Thank you - When I turn the key on, I can hear the fuel pump hiss. When I turn the key on for a few seconds, then off, then on for a few seconds, then off, three times - the car starts faster but still not right away.

What does turning that knob on top of the MAS relay do?