An often asked question, as it varies based on model and chassis and year. On Freightliner DPs, almost always, the tow fuses are located on the drivers side at the rear of the coach. On my Vectra, with the side radiator, the fuses are at the very back of the driver's side behind the hinged radiator grill. Other model owners have found theirs slightly forward in the power compartment behind a screw panel, usually upper right as looking in from the outside. Look for about 6 screws holding a panel.
Ed & Joie
2004 Vectra 40KD
Freightliner Chassis and Cummins ISC