Electrical problem

Stringer Family

I am new to caravanning and new to the site so apologise in advance if this is a simple question.

I have Recently had a double electric socket added to my car and we have purchased an early 1990s Eld is wisp 400/4.

When I connect the van to the car the fridge will not run even though it is switched to the car and the engine is running.

I have read there was a change to the wiring on sockets around 1999. 

I presume my car is wired up in the new fashion, does that mean that I need to make a change to the socket on the caravan or wiring in the caravan?

 

Graham