I will try to explain as best I can as my husband is not here to help me word this properly!

We have a 1997 Hi-Jet which has recently broken down. Out of the blue after running for approx an hour and a half, he tried starting it after stopping for petrol, but it would not do anything at all. After checking all the obvious things it was left until the morning when he removed 2 relays (DENSO 056700-9160 12v) and one of them appeared to be discoloured, as if it were burning out, they were replaced and the vehicle started and he was able to get home. These 2 relays are about half the size of a matchbox and were found under the brake fluid reservoir, next to the dim/dip relays. He still does not know what these relays are actually for and what they they do, so any help on that would be useful.
Once the vehicle was home he checked other relays and the fuel pump, and they all seemed fine, and he has used the car with no problems since monday until last night when it broke down again, but this time whilst the car was moving. The only link with the breakdowns, is that on both occasions the headlights were on. We are baffled. Any suggestions would be really appreciated, thanks, Karen