Ignition Switch

From Citroen SM Wiki

Reducing the load on the switch

The design of wiring related to the ignition switch is a weak point for the SM. Specifically, starter solenoid activation current all passes through the ignition switch. As the switch wears out the resistance increases. Poor starting is one effect. Switch melt-down is also possible.

An extremely common modification is to fit a Ford solenoid or a starter relay.

Fitting a starter relay

  1. It fits very neat if you just buy a DIN relay and matching socket. Fix the relay on the right oil canister holder's lower side (difficult to tell, but take a look-it's obvious). Or put the relay next to the voltage regulator, which is where the neutral interlock relay is located on cars with automatic transmission. Note: It is not necessary to do this modification if you have an automatic transmission since the neutral interlock relay already performs the function of taking the load off the ignition switch.
  2. Find the cable which comes up from the starter and consists of two cables: A thick one, and a thin one that splits near to the right brake.
  3. Open the cable there, and make the following connections:
    1. Battery PLUS to the relay socket.
    2. Ground to chassis -- take the point where the screw is screwed into the frame (the one which keeps the big water tube in its place)
    3. Relay output -- (the switched battery PLUS) to the wire that goes down to the starter- it's a MALE connector.
    4. Relay sense wire -- the one coming out of the original loom, it is a FEMALE one.
  4. Test: relay should click when turning ignition, as the sense wire draws the relay, and PLUS is switched to the male connector which then gives this plus to the starter.

Ford Solenoid

Commonly done, but is overkill, since the starter has its own solenoid.


Ford Voltage Regulator

In order to reduce load on the ignition switch, fit a Ford voltage regulator, which has an internal field coil transistor so does not require power from the ignition switch (this is a common modification for the Citroen DS).

See also