I don't know if you have the instructions or not so I'll include a link.
https://www.truckspring.com/installa...sm/vsm-920.pdf
One model includes the brake lights and the others don't. The correct bulbs and flasher have to be used for the voltage applied. The strap for the switch head has to be well grounded to the frame ground of the car for it and all related components. If there are any bare wires anywhere in the system whether internal to the switch head or external to the bulbs & power source, there will be a short to ground. Follow the instructions for the unit at hand and insure all connections and conductors are in good condition.
Burned fuses are a sign of a direct short to ground in most cases. High resistance levels due to loose wiring connections will cause heat near the area where the resistance is high. The turn signal flasher switch or signal stat works off heat for it to break the circuit and cause the flash. If there are LED type lights in the system it can cause a problem where the signal stat won't function properly. Using only two bulbs instead of all four may not give enough electrical load for the system so keep that in mind too.