Originally Posted by Diseasel300

Use a 12V light bulb and make sure that your power and ground are actually good solid connections that can handle current. You can be fooled by using a multimeter, sometimes you can read voltage, but the circuit is faulty enough that it can't pass current. A light bulb will light if the circuit is good, but won't if it's bad since it draws a fair bit of current.

Also worth checking is the fuses themselves. If they're the aluminum type, hit the trash with them and install the modern brass or copper replacements. The aluminum style are notorious for developing fractures and failing at inopportune times.