Generally, it would probably be easier to run the wire under the car. The fuse should be placed very close to the battery, and then you could follow a brake line or similar existing line (but not near the exhaust system). Be sure to use fuel/oil resistant wire. It could then be passed into the boot through a grommet or pdssibly a socket could be placed next to or in conjunction with the caravan's electrical connector.
Does your 850 have prewired towing electrics? If so you should find a 10 pin connector in the boot area probably under the floor in the lefthand corner. This would have a Volvo part which connects to this connector and goes to the towbar connectors. Does your caravan have 12N and 12S connectors? If so take a look on the VOC website where you should find the correct wiring diagrams for all UK/Europe car to caravan connections. These include the new
13 pin Euroconnector. If your car does not have the prewired connector in the boot area then it will be a little more complex but should be covered on the website. I would advise routing any wiring from the front of the car through the passenger compartment to the boot. It can be fed along the side of the compartment under the trim panels.
All the best, Peter.
700/900/90 Register Keeper, Volvo Owners Club (UK).
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