2005 Pre Heater Lights & Dash Number

Hi all,

I have just got this van and the pig tails come on after the engine has fired for about 30 seconds and then go off? Can anyone tell me what this means? I have had a look through the manual but I can't find any reference to it?

Also at the same time the van fires up the digital display beeps and says -720 on it. Does anyone know what this means?

Thanks,

Andy