Beneath the main dash panel is the … er… lower dash panel. This panel accommodates the control switch for the fan heater, the cold start knob (and switch) and as an optional extra… a blank panel where a hand throttle can be installed. (The latter typically found on diesel models fitted with some form of PTO drive appliance. Fitted For Radio (FFR) military vehicles also had a hand throttle to increase the idle speed of the engine when the vehicle was stationary for long periods in order to power the radio sets…. but I digress.)

For some reason, the cold start switch assembly fell through the gap of small parts, stripped, cleaned, and repainted so in between other bits and pieces yesterday, I gave it a bit of a tidy up.

The cold start knob / switch (whatever you want to call it) performs two functions….

1) It operates the cold start setting on the carburettor. Pulling the knob out restricts the volume of air being drawn into the engine making the fuel / air mixture “richer”.

2) It also switches the warming light on the main dash panel, informing the driver, the choke is open.

Found languishing on the shelf
Stripped, rubbed back and ready for primer
Painted and ready to be put back together
Barrel and switch actuator. Note the small hole in the top of the barrel. The actuator has a small protrusion that sits in the hole…. (can be seen in the picture above with the primer)
… the position of this protrusion matches up with the narrow section of the switch “piston”. Once the knob is pulled out, the protrusion pushes the actuator up, the end of which operates the switch… Hey presto, it closes the circuit and the light comes on on the main dash panel.
Cold start plunger back together
Original switch installed


The other switch residing in the lower dash panel is the heater switch, also called a  rheostat or potentiometer . The original one had only one setting…. ON FAST. It should function in such a way that one can regulate the speed of the motor by how much the rheostat is rotated.

New Lucas rheostat and knob. Original rheostat and knob
Heater switch installed in the panel
Cold start and heater switch
From above. Heater switch on the left, cold start on the right.