I fitted a similar unit recently but used a interface from Tim of TEB Technology [PM me for address] & the RR float switch header tank cap coolant level sensor PRC7925, copied from my posts here Fri Sep 18, 2009 fitted the interface today, all working & I've used the water in fuel warning light of my Td5 warning light pack to tell me when the level is low, the green led on the interface is ON when coolant level is OK, so I've a light for both good & bad notifications.