Because of things like this wad of wires going through the front of my AS, and through the floor of my AS, I use a Power Probe. This circut tester is for 12 or 24 volt systems. It will check continuity, determine polarity, check voltage, check for a bad or ineffective ground, help trace short circuits, activate or power on things like a fan, motor or a light. You can also insert the probe into a trailer pig tail and check to see if the tail light, brake light, running light, or turn indicator is activated. The probe also has a built in circuit breaker that will trip so as not to burn up if you power it on and there is a direct ground. It also has modes or functions that will allow you to check things like a battery crank test, or trace a loose wire or connection that periodically drops a signal, such as a speaker wire, etc.. A good trouble shooting tool with a lot of functions.
1997 25' Safari
2012 Chevy Silverado HD 2500