ducato camper electrics

Hi Everybody, I,m a new mamber and wonder if someone can help me, i have recently bought a 1992 Ducato Hymer camper van. all was going great until I went to use it last wekk and the battery was flat.I jump started it and off we went but after a few miles the alternator/battery light came on. Over a few bumps it went out but in the end it was on all the time. I have checked the alternator output and it seems to be about 14v. Above the battery is a white box about 2" x 3" x1" in size when i wiggled the connection the light went out but after a test drive it came back on. Does anyone know what this box does? To complicate matters being a camper van it has a leisure battery dual charging/electric system. I would appreciate any help or clues anybody can give me.
thanks. dave.
(having sold my boat to buy a camper i suppose i registered with the wrong name really!!)

ive just joined the club, and have also just bought an old hymer motorhome,1987 vintage,2.5 TD,and trying to find all i can about it,i do have a wiring diagram for the hymer bit stuck on the back,as you have probably worked out the aux batts under the seat along with two or three relays dependant on model,as far as i can see,the aux batt will only charge when the engine runs and then disconnect when stopped,this ensures that you allways have a full main battery,i would check condition of aux battery,also relay contacts are not welded together.
I to have a black box above the main battery' and yes me wondering what for , ive seen it refered to as 2044029 bitron, as far as i can see on my van it puts 12v to a single glow plug situated in the inlet manifold,and also works a solenoid valve mounted next to it, i presume this forms part of the cold start system,a hot mist into the manifold ?its the first time ive seen anything like it, I cant seem to be able to get any info on this system, so perhaps someone out there can shed some light.

Hi Smithies, thanks for replying. You are right in thinking that it has something to do with the glow plug/s as i disconnected it and tried to start the engine and the glow plug light didn,t come on and it wouldn,t start although it turned over.The box on mine is white but also has Bitron on it. I,m going to ring Fiat today and Hymer uk so I,ll let you know if i get any further. It,s typical i,ve got a Toyota car and Haynes don,t do a workshop manual for that either.Next time i,m going to buy a manual then get the vehicle!!!
Cheers, dave.

Hi all. well it,s taken a time to sort out, but after fitting a new alternator, on the recommendation of a "Hymer Specialist", and then taking it to a garage who sussed out pretty rapidly that it was a loose wire behind the speedo/dash board. Oh well we live and learn. all fixed now but unfortunately too late to take the kids away at half term. Still no luck with a manual or wiring diagram.
Cheers,dave.