Identifying the function of the three relays on the side of the enginebay.

[rutger kohler]

There are three relays mounted on the left hand side of my RHD 280SL enginebay, as you stand at the front of the car. Could someone please identify what each of these are for starting with the one in the front. My car was picked up in germany so does not have the american feul emmision setup.  Also are there any other relays apart from the blinkers or indicators on the car plse?

[Peter van Es]

Still check this page in its entirety... http://www.sl113.org/wiki/Electrical/EmissionControlSystem

[rutger kohler]

Hi Peter, thanks for that.  I can now see the three relays and they are marked.  I guess the relay marked CSV controls the fuel solenoid valve I asked about, on the air inlet manifold?

I also guess FIP stands for Fuel Injection Pump, and this relay controls the Fuel shutoff Solenoid, shown in the photo next to the 17 degree switch, which my car doesn't have?

[ja17]

Hello Rutger,

Not all starting systems are the same depending on your year and original delivery location.  If you have one solenoid on your injection pump (1969) the solenoid on the injection pump is a cold starting aid which activates each time the starter is activated. The front most relay should be the one for this device on your W113.  The middle one should be for the starting valve on the intake manifold.  The rearmost relay is a windshield wiper relay. On your W113, most likely the starting valve on the intake only activates below 95F (35C).

Always check the cold start valve (CSV) to make sure the device is functional first. (test it with a hot wire). Next  check to see if  you have power going to the CSV when starting the engine cold. If not check the relay (contacts corrode). Terminal #86 on the relay is positive and is hot on ALL  starts. The relay is actually tripped by switching on the ground (earth) #85. which is regulated by the thermo time switch.  #30/51 is the positive  lead going into the relay and #87 is the positive lead going to the CSV. Remember however that the negative "earth #85 is the line which switches the relay on and off via the TTS.
 The thermo time switch is located on the pod between the cylinder head and IP. It has two wires going to it. One terminal is marked "G" (small screw), the other is marked "W" (large screw).  The W terminal supplies ground (earth) and activates the CSV relay during cold starts. Temporarily installing a ground wire to "W" is a way to test to see if the Thermo time switch is functional. If the CSV works with jumper wire, then the TTS is most likely bad. If the CSV does not function with the jumper wire, then the solenoid, wiring or CSV itself is the problem.

The injection pump starting solenoid should activate during any start (hot or cold). The two front relays are the same part and are interchangeable. In the contrast the CSV solenoid relay  functions differently because of how it is used. It is switched on and off via "earth" #85, the relay for the Injection Pump Solenoid is supplied with constant "earth" at #85 and the relay is activated by positive current being switched on and off via the starter switch, then  fuse #6 and  then terminal #87 of the relay.

[rutger kohler]

Hi there, thank you very much Joe, this is a very detailed and useful description of my system.  Will print off and put into my folder on the car.  Much more than I had hoped for.