Backup light fuses blows

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One way to help track down an intermittent short is with the process of elimination. Disconnect everything related to the fuse that’s blowin, one circuit at a time until the fuse failure stops. That gonna tell you what circuit is responsible for the fuse blowin. More times than not an intermittent short is the result of something heatin up and breaking, or making contact. Other times it’s or somethin that is loose and is making periodic contact. A lot of times it’s loose or corroded connections. Defective switches often cause an intermittent short. Try jiggling the circuit wires and wire harnesses to see if the circuit voltage or resistance changes or if the fuse blows again. Also check any wire connectors in the circuit. Make sure they are on tight, and free of all dirt rust and corrosion. Also check for a wire (or wires) that is rubbing or has chaffed away some of its insulation. That can cause an intermittent contact which can cause a short. So again, wiggling suspicious wires will often reveal the problem. A lot of times an intermittent short can be temperature and environmentally sensitive. When does the short occur? Does it occur only happen when the engine is hot, cold or after the circuit has been on for a period of time? What is that period of time? Is it always the same and constant? Does the short occur more often in damp or wet weather. Usin a hot air gun or hair dryer to heat up wires, circuits, connectors, switches and relays can sometimes help identify troublesome component or components..