fuse

hi i just want to know should i use a fuse before or after the relay thanks

In general we fuse each circuit after the relay. This is essential if you're running circuits with vastly different current draw off a single relay as fusing pre-relay would mean that the fuse would need to support the total current of all the circuits which could be enough to damage some of the lighter circuits if something went wrong. Zac covers it nicely here: https://www.hpacademy.com/dashboard/courses/practical-harness-construction-club-level/practical-wiring-harness-design-skills-power-supply-design