I figured I would share a tip with you on a way to trace down those pesky short circuits. You know the ones that blow the fuses and make you go nuts. This tip works on a dead short to ground problem. What you need is a bulb with a wire soldered to the positive and a wire soldered to the ground. The end of your wires need a terminal end to connect into your fuse center. Glass fuse style will need a female connetor to slip over the tang that grabs the fuse,newer plastic blade fuses will need a male flat spike to slip into the fuse slot. Now turn off all components in the circuit that has the problem. Connect your new test lamp into place by removing the blown fuse and jumping the fuse circuit with the lamp. This now puts an electrical consumer in the circuit. No more short to ground. As long as your short is present the light will illuminate. Now start going through all the components of the circuit and disconnect one at a time and watch your lamp.If a component is shorted to ground then the light will go out when unplugged. If you unplug all the components and the short is still there you need to start jiggling the wiring and disconnecting any harness connectors like a bulkhead connector. HERE is a non HAMB example but it shows a major problem made simpular: I recently had a major short (multimeter showed 35 Amps) when a 88 firebird I reassembled was connected at the battery. The power leg down at the starter was shorted when I connected it. The factory print showed this power wire to feed half the engine bay and a portion of the interior....I used my test lamp gizzmo by connecting one side to the battery hot and the other to the battery positive cable. I then started unplugging everything in the engine bay,.....sensors, alt, ac comp.,.....but still the short was there. I then unplugged the bulk head connector and the short dissappeared (light went out). I then left the connector apart and connected the battery fully. I proceeded to jump the pin on the harness connector to the one on the firewall with the test gizzmo and till the circuit with the short lit up the lamp. This circuit is now narrowed down further.......from the major brach that it started as. I finaly wiggled the harness till the light would flicker at one end of the harness. I found I pinched a wire on the edge of the dash when I reassembled the interior. The lamp I made is made up of two lampsockets from a volvo(I used to work for them) I use two in parrallel in case I bump it and a bulb blows. Kinda unnecessary but it's what I use. If a pic is needed let me know. ALSO...feel free to use this post for other useful electrical tips on troubleshooting.
I would also suggest using a small guage wire on you lamp which will act like a fusible link in case something goes wrong. But as I showed you I traced down a 35 amp short to ground with 16ga wire on mine. Your lamp acts like the consumer in a circuit and you are on the hunt for the ground making it happen. REMEMBER the simple electrical circuit consist of #1-Power source (battery)#2 consumer(your lamp) and #3 ground (the short you are trying to find)
Good idea,I always use a volt-ohm meter but a lot of guys that are great mechanics refuse to use a meter.
God love you I am going crazy tring to find a short on a china scotter will make a test light. thanks
I fix aircraft and have used the light bulb trick you described. The preferred method (when you have the tools) for me is to use my old analog Simpson meter. Depending on the light bulb you use, while shaking wiring down, the light may or may not dim as you get close to the source (if it isn't totally grounded out) An analog meter I find usually will start to twitch giving you an indication that you are close. An analog Simpson (or cheapy Radio Shack) works fine when you can see the meter. The light works fine if you are in an area where you can always see the bulb or light it produces. My Fluke digital meter has a tone that sounds when the circuit is grounded. Shaking the wiring when you can't see the meter or light you may hear the meter tone disappear. Then there is the intermittent short that comes and gets you like when it rains or after hitting a bump! Isolate the circuit to just the wire and a megger usually finds these things. I have a 1950's era hand crank that puts out 500 VDC, this typically can jump a spark where you can hear or when dark enough see the short. If it is a dead short, the meggar will instantly disapate. If it is leaking, then the megger will slowly disapate the high voltage, you end up replacing the wire segment. Also note that the light bulb method is preferred when looking for power on a circuit over a meter when the condition has been intermitent. Placing the bulb and powering the circuit pulls amperage through the wiring, while a meter will tell you the voltage and pull very little amperage. This will not identify poor connections thorugh connectors or splices. And don't skimp on the lights, at least use a tail light bulb. They are easy to solder wires to.
By no means do I toss my DVOM meter in the corner! I love using my meter and understand it well. ...This is just a trick I found that lets you see a visible light source and leaves your hands free to "explore". Also brought up was the possibility of the light not responding fast enough if you are shaking down the wiring and it momentarily goes out but the light doesn't respond fast enough. I have never had this happen but I guess it would be possible. I guess you could use a LED bulb. These illuminate at a higher speed than the ole Thomas Edison incadescent.....but would offer a lower load to the circuit
How about doing this with a buzzer ? Then you could do it without continually looking at light. Frank
This is useful tip/tool that I have used for years. Thanks for posting it. Buzzers can get aggrivating but work also. Love my simpson, and my fluke and my amp meter. Now that aircrafty stuff sound like the shit! What is a meggar? any pics
a megger is kinda like a magneto....generates the voltage by cranking a handle...... i have little experiance with it but I believe that is it in a nut shell
A megger is used to test insulation of high voltage wires. It will detect a breakdown of insulation where a higher voltage can arc to ground. It is used say in a check out of trolley where it runs on 600 volt DC and has an intermittent short.
I use a megger at work to test electrical motors that don't show a fault to ground with an ohm meter. Many times you can find weak spots in the insulation that normally wouldn't show up until the motor was loaded and heated up. We've also megged out feeder lines prior to heating up equipment for the first time. Nothing says "Oh S@#t" quite like having a new set of feeders blow sparks when you flop the handle at the service. Meggers are also useful demonstration devices for newbie electricians...don't ask how I know. Let's just say I'd rather pee on an electric fence again than be bit by the megger...
Another electrical test that is rather simple is the amp draw test/parasitic drain test. I know this one is a more common tip but to those of you a little shy on electrical it is a good test for those batteries that wont last a day or so when you park the car. Set car as if leaving it for the night.(all things off) Remove the negative cable from the battery. Get your meter set to the AMP setting. (Most meters have a seperate jack for the leads and can handle 10 amps and are internaly fused). Now connect one lead (red) to the loose negative battery cable and the other lead (black) to the battery post(negative). The reading is acceptable from 0amp to .1amp (or 100mA depending on your display) Your amount of drain is dependant on what you have consuming with the key off. Things like clock,radio(with clock or station memory), computer (if running fuel inj etc) On newer cars I see up to 100mA (.1A) for all the garbage on them electricaly. On the older cars alot of times it may be 0A. Make sure when you do this test all things are off as they would be when you park the car for the evening. Even a dome light or glove box light (if you got one) will make a big change in the reading. NOW if the reading is too high then start going through the car and check for anything active. Then start pulling fuses and disconnecting any possible electrical part until the reading drops to the acceptable range. Repair as needed. Good luck! Everyone please post a trouble shooting electrical tip here.I good use a new "trick"
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