1974 450 sl

[maltapaul]

Hi, I have a 1974 450 sl that could not start, there is fuel and spark while cranking. According to the not so helfull manual, (Correct me if I am wrong) the top relay above the fuse box on the passenger side towards the front is the fuel pump relay and the one right below it is the fuel injetion relay. My problem is that when I took off the relay for the fuel injection 2nd from the top the relay base came appart and the 5 wires came off and now I do not have a diaghram of which wire goes where on the 5 terminals on the relay (85-86-87-87A-30). Does anyone know where these wires go?
Thanks for any help.

[cth350]

If the relay itself is busted, chuck it. They're like 3$ each used. You should be able to swap a different relay for it.

On the other hand, if the wiring connector came apart and you have bare wire ends from the harness in front of you, let us know the colors on the wire ends. You should see a base color and some stripes. For instance Black +violet stripe or all brown (no stripe).

-CTH

[maltapaul]

Thank you for your interest, Now I am not sure if it is the fuel pump relay or the fuel injection relay. According to what I read, the top relay towards the front of the car is the fuel pump relay and the one just below it is the fuel injection relay, this is the one that all the wires came off. the wires are:
Brown with Blue stripe (thin wire)
Blue/Black/Orange (thick wire connected with wire below)
Purple (thick wire connected with wire above)
Black with Purple stripe (thick wire)
Black with white stripe (thick wire)
Purple with white stripe (thin wire)
Now what I need is to know where these 5 wires ( the second and third wires are one) go on the relay numbers ie: 85-86-30-87-87A
Then I still have to deal with the no start problem after that.
Thank you

[250 Coupe]

The schematic for the '74 450SE is here.

The engine manual is here.

Good luck,
Michael

[maltapaul]

Thanks Michael for the link to the diagrams. I am still confused as to which realy I am dealing with. Ok there are 2 banks of relays 3 towards the front of the car and 4 towards the rear. On the diagrams you sent me it says (1) Relay fuel pump (2) Relay starting valve (3) Main relay electronic injection, are these the 3 relays on the first bank towards the front of the car??????? Now I took off the 2nd relay on the front bank and there are 5 wires but the diaghrams show only 4 wires on all the relays in the diaghrams, plus the wire color codes do not match either, do I have the wrong diaghram?

[cth350]

The 450se and 450sl wiring have differences in the cold start valve arrangement. That diagram won't help you.

There is a similar publication for the 107 chassis cars. You need the "Electrical troubleshooting guide". You can (and should) buy it direct from mercedes at 1-800-for-merc.

-CTH

[ctaylor738]

85-86-87-87A-30

From memory - I am travelling and have no information

30 should be 12v - either always hot or with key on
86 is ground - should be brown
87 is out to pump, should be the big r-w-b wire
85 MAY be tach input (from ignition unit)
87A - not sure

[maltapaul]

Thanks guys, I have ordered the electrical diaghram on CD from Mercedes. If anyone knows what those 7 relays are for or the first 3 relays on the front, please let me know. Thanks again. I will let you know the outcome.