1988 R107 300SL - Won't start, fuel pump relay?

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Active Member
Jan 25, 2016
UK, Hong Kong, Japan
R107 500SL, W124 E500 LTD, W124 AMG, W211 E55, E30 M3, CSL, Z3M, 355, 550, 360 CS, 964, NSX, RX-7

A friend of mine owns a 1988 300SL and it's refusing to fire up.

I have read some place before that the fuel pump relay could be the cause? Anyone else had a similar issue or could help diagnose what it may be?

Thank you very much
Non starters are normally down to lack of fuel or spark [ assuming they are turning over on the starter] Fuel pumps rarely fail but the FPR fuel pump relay often does. You should hear the pump "prime" for a few seconds on initial ignition switch on if its OK. other common faults on the M103 6 cylinder engine are HT ignition problems with the forward facing distributor [ damp being one if the cars been sat around a lot] Other possibility is a faulty ignition switch itself which powers all the vital engine electrics. Really its a case of doing various tests to eliminate the various possibilities.
some years ago I had a 107, I fitted pattern part dissy cap and rotor arm, rotor arm lasted about 1000 mile, burnt hole smack bang in middle, lookly I had old one in boot so after 10 mins were running again, after that fitted genuine part and had no problems after that. so worth removing and inspecting it as it could have cheap part fitted.
I had the same problem with my 89 R107. Had taken it into my loacal Indie for a slight fuel pump leak which they cured only for the car not to start again. Turned out to be fuel pump relay which is situated behind the glove box lining. Replaced and started first time. I believe they are approx £190 from MB I bought a used one from Merc Man for £46
ve they are approx [B said:
£190 from MB[/B]

:crazy:Must be dam fancy relay to justify that price.
Thank you very much for sharing your experiences. I've passed the information on to my friend and will report back with the update! :)
Would anyone happen to know the part number for the fuel relay. It's a 1988 R107. 300SL.


Thanks again.
Its slightly more complicated than a simple relay being two stage. The first stage comes on at ignition switch on to prime the system the second stage requires an" engine running" signal to stay switched on pumping fuel- this is a safety feature in the event of a crash to stop the electric fuel pump supplying fuel to a stalled engine increasing the risk of fire. you can test the realy by shorting the main connections to see if the pump will run [ continuously! till disconnected again]
try this

Mercedes-Benz 300SL 107 Fuel Pump Relay 0035452405 | The SL Shop
I would point out that the fuel pump relay is supposed to be a sealed unit but my Indie managed to open it up, only to find the problem was dry joints. A little soldering later and all was ok. Kept the used one as a spare. Maybe that is the problem, worth a try before buying a new one.

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