A case of the shorts.

[dwaynedmonnett]

I have had a few times when a short in the wiring was very elusive and hard to find. A friend had a short that was progressive in nature, the proportioner valve in his hydraulic brake for the towed vehicle starting blowing fuses. At first he would just replace the fuse, as it was not apparent why the fuse was blowing. He then upped the size of the fuse. I told him not to do that, as he could turn cause a bad problem to become a disastrous fire. As a trouble shooting procedure, I found that using a head-light in place of the fuse helps chase down the problem. If there is a hard short, the light will light up full brilliance. The light will only pull about 5 -6 amps, well within the capability of the wiring harness. Then by following the wiring harness away from the light, disconnecting anything connected, the light will extinguish when the short is removed. As it turned out in my friends coach, the installing mechanic had not checked for brake fluid when he made a splice into the main line to feed the proportioner valve. There was a very small leak, the brake fluid was making its way down the pipe and into the windings of the electric operated valve. Over time the brake fluid was desolving the insulation on the wire and causing the wires to short out. It took a while till the valve got to the point where it would no longer work, and began blowing fuses. The valve was replaced and the leak fixed.

[Melmoses]

Smart idea! I will store that in my "what if" file just in case. Thanks! I know your friend had to appreciate that a whole lot!

[wa8yxm]

Used that trick many times.

Light bulbs make great current limiters.

[Koop]

Yes, a bulb limiter is a great idea. I build tube guitar amplifiers and always use a bulb limiter on initial power up - the bulb will burn bright for less than a second, once the capacitors charge it will dim telling me all is well. If the bulb burns bright, I have too much current indicating a short somewhere.