1991 DAF 45 Starting Problem?

I have just fitted a new starter motor, batteries and isolator switch on my DAF 45 horse lorry. It started up on turn of key once all re-fitted and I ran it to charge the air tanks. I then swithced off to check restart. It would not then turn over or re-start - no clicking apart from relay in the dash. In addition when isolated the dash lights and ignition still light up and all electrics in cab still work. On the old starter there is an additional relay fitted where the small wire from the solonoid goes into, I believe this is either part of the leisure battery charging system or for starting the onboard generator. Any suggestions??