Glow plug controller

I have just got a 1985 M1008. the glow plug controller is missing. I installed a switch at the relay and it starts fine. I would like any info on installing a newer version controller they say in 1988 there were improvements. I wanted to be able to use the key for starts with the glow plug light functioning any help would be welcome, maybe it would be best to install the stock controller and leave the switch for back up. However if I can update the controler and get rid of any known problems that would be nice

Thanks