Last4KRunning

I posted this in another section of the forums. This info can help find shorts in any electrical circuit. Using a lamp in place of a fuse allows you the time to find a short while protecting your wiring harness. I hope this helps.

I have worked in industrial maintenance for over 15 years and with all kinds of electronics for many more years. I currently work in a dairy food plant. Our equipment gets washed down with water all the time every 24 to 48 hours. As you can imagine water gets into everything. Just an observation any water tight box always gets a leak at the top but never leaks at the bottom so it can fill with water and stay full..... In any case many times the first sign of problems is a blown fuse. The next sign is a pile of blown fuses. When the fuse is for the 24V control circuit power supply that feeds every switch prox and photoeye it can be a real bear to find the short.
So here is my solution (Note I know I did not invent this!) Pull the fuse that blows and replace the fuse with a lamp rated for the same voltage. In your case 12 volts. I would use a 1155 brake light lamp.( get a socket with pigtails add 5-6 feet of wire. Add connectors that will plug in where the fuse went.) This draws about 2 to 2.5 amps to light fully. A normal circuit will not draw full current through the lamp and it will light dimly. When a short occures the light will go to full brilliance. In your case the lamp will stay bright untill you find your short! (THe bulb will get very hot after awhile. Make sure it cant burn anything.) With the long wire you can hang the bulb up where you can see it while you look for the short/s, wiggle wires and or unplug things. The lamp limits the current to a safe 2-2.5 amps this will not melt your wiring. This works out to about 24 to 30 watts of power at the shorted spot. This many times causes heating or some smoke at the shorted component that you can now find. If you can't find anything start unplugging parts. If you want to get fancy you can purchase a DC (make sure it has a DC clamp range) Clamp on ammeter. This test meter has jaws that open and go around the wire you are checking, when the jaws close the meter shows the current flowing on that wire without having to cut the wire. One of these meters for automotive use run around a little less than 100 dollars. With the bulb and the amp clamp I have found a lot of shorts and shorted components. Look for the wire carrying all the current from the bulb. (note measure the current on one of the wires coming out of the bulb to get the base current flow.) If you need more current or less use different bulbs. For more current you could use a headlight bulb, it will draw more current. I would be carefull doing this though. The 1155 should work well. Also if you pull all the other fuses the only wires carrying current will be the circuit you are interested in. You can also get fuse holders at the automotive stores and make up a fuse with extension wires, I made one of these and then put on some spade connectors the same size as as fuse. I could then plug this into the fuse box and I now had a place to clip on my clamp on ammeter. Then I could measure current draw on each circuit.

Look for the Electronic Specialties ESI 687 Low Current AC/DC Clamp Meter on the internet or do a search for DC clamp on. You want a meter with the small jaws that will fit in more spaces. I purchased one of these ESI 687s a few years ago. You may find other brands of meter that are cheaper.

Here is another nifty ampmeter for troublshooting your wiring. I have one of these also. I found the listing on E-bay for an example.(Automotive Current Amp ATC Blade Fuse Meter Tester
Item: 370571043712) Mine came from a paper catalog.

Tim Laing