[Michael C Henry]

If you figure what that switch is operating check if you have an fuse rated for the amount of curent excepected to be needed. Second, check that the connections to the apparatus being operated. Some fans and fuel pumps have a ground wire that is a added absolute ground but can operate by using the ground provided through its metal housing. If the wirng were reversed then you may have the hot positive wire connected to a ground which would burn the fuse..
I was working on an old peice of equipment and removed all the gauges and switches from the dash(all old small dirty stif black wires) the wires were all dirty very small numbers and stiff. The stiff asspect worked for me most of the time. I missed a pair out of three and a light and had one hot wire hooked directly to the ground on an electric tachometer. I tried to temporaryily use a circuit breaker in place of the fuse but had problems so I ended up disconnecting the wire from the back of the fuse pannel that that fuse supplied and mounted another fuse.
I then temporarily connected my 12v 24v test light in series between the out of the fuse and the wire it had been connected to. Man was my test light bright but it acted as a current limiter. It wouldn't let anymore current through than the filliment in the bulb would use. With the test light leaned aganist the windsheild I started inside with the gauges and switches which had indivdual wires instead of multiwire plugs. As I unplugged the tachometer, the test light dimmed a bit and a low air preasure warning buzzer that hadn't been heard from in a while started making some noise. So reexamined the lay of the old stif wires. I swapped a couple of wires and everything was then correct .
Another tool that woul be a great addition to your tool set . "Power Probe " comes as a kit in a blow molded box, alligator clips, cigerett power plugin, a good lehgth of coard, and an extension cord . It has it's own lights to work in limited light ares . It makes different noises and had different light for completed circuits and dead shorts . It can be used to directly energize electrical units and has a built in circuit breaker.