vanagon heater booster operation

i've just recently acquired a 1982 diesel vanagon equipped with a heater booster - but no owner's manual. does anyone know how the heater booster is supposed to be operated? it is not working right now and it would be a lot easier to fix it if i knew how it was supposed to be turned on!!

It's a fairly complex petrol heater. The Bentley Vanagon manual covers it in detail. They are available used on eBay at reasonable prices.