Volvo VNL AUX fan Switch malfunction

Do you know if the truck came with that switch set up as manual fan, or is it something somebody added in? The 98 Volvo I had, came without a fan on manual switch, so I made my own. All I did was run two wires from a cab switch out to where the 2 wires went to the solenoid on the engine which controlled fan on/off. When I turned my switch on, it interrupted the power to the solenoid, which turned off the air to the fan clutch, and made the fan come on. Fairly simple to do if you understand basic wiring, and air solenoid operation. Could be your switch packed it in, in which case all you have to do is pick another unused aux switch, and swap the connector over. Anyway, hope this gives you some ideas where to start.