leyland roadrunner ?

Hi I am in the middle of restoring/rebuilding a motorhome I bought last year, orig it was a leyland, wright consort bus, then about 15yrs ago it was converted into a motorhome/race truck.

the chassis is a roadrunner 9tonne 1989 running a leyland/cummins 6.7L 12v

the engine runs sweet and has that wonderful cummins 6 sound,

the one thing I am not sure about is the speedlimiter due to the fact it is reg'd as private hgv motorcaravan, and It has been downrated to 7.5t i dont need the speed limiter. it has a speedlimiter box fitted under the dash but the question is how does it work? there is only a single cable going to the pump direct from pedal. and there is a box attached to the chassis with a drop link to the front axle this electrically connects to the speedlimiter box