Shorts and Drains how to find

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Shorts and Drains how to find

Postby noxqus » Wed Jan 06, 2021 8:30 pm

After working the last 20 years in automotive electrical field I have learned some tricks on how to find shorts and drains in cars and trucks.
Shorts which all of sudden have blown a fuse have given you the first glue. What does that fuse protect? Let’s take the lighting system as an example. Where could that short be? Here is how to find it quickly without burning up any wires. Pick up a 5 amp circuit breaker at your local parts store. Most circuit breakers today are bladed fuses that plug into sockets in the fuse panel. You will have to take a blown glass fuse for older cars and solder a small wire to the ends of the glass fuse and to each blade of the breaker. Once you have completed that, plug the fuse back onto its shorted circuit and turn on the lights. The breaker will start clicking as it opens and closes because of the short. Now comes the fun, go around to every light on the car and cup your hands over the light and see if it has a glow appear and then go out. If it does the short is not on that circuit, continue to the rest of the lights until you find one that never has a glow. The one that doesn't glow is the circuit with the short. Let’s say it is a front parking light, first step is to remove the bulb. If the bulb is the problem the breaker will stop clicking and the rest of the lights will return to their normal brightness. If the bulb is not the issue something has cut into the wire connecting it to ground. You know at this point what wire it is now just following the wire until you find where.
You get up in the morning and your battery is dead, you drove it around yesterday, started it several times no alternator light has come so it is charging. You charge the battery have it checked and it is ok, but the next morning it's dead again. You now think there is a drain. Here is a good way to find it. Take a test light with an incandescent bulb in it, LED will not work, other things that will work are dash light socket and bulb side marker light socket and bulb will do the job. Remove the positive cable from the battery Connect one end of the test light or whatever light you are using to the positive post and the other wire to the cable. With everything off and doors closed and hood light bulb out of its socket your test light or bulb setup should not light, if the light is on something is drawing current in the car. The only thing that will cause this is always hot circuits. Under the hood the most likely culprit would be the alternator or regulator if you have and external regulator. Disconnect the wires from the alternator if the light now goes out the alternator diode trio or Rectifier Bridge has an issue and will need to be replaced. Most just replace alternator. If the light is still on and you have a regulator remove its wires if light out regulator bad. If light remains go into the car and remove the dome light fuse and then one at a time replacing them after you check remove each fuse in the fuse box until the light goes out. Whatever circuit turns the light out will be the problem. Most issues are relays, in car switches like glove box switch.
This works on all none computerize vehicles, for those vehicles you will have to purchase some sophisticated equipment, my advice go to someone that does, as the old ways as describe above will kill some high dollar parts quickly.
Last tip if you are going to put in a relay for some add on in your vehicle and this vehicle is computerized be sure the relay is internal diode protected or internally resisted, diode is better. When a relay is shut off it can drop a considerable voltage spike on the line killing electronic components.
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Re: Shorts and Drains how to find

Postby 74_Vega_GT » Wed Jan 13, 2021 11:21 am

~ Great Write-up. Thanks for posting this.
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Re: Shorts and Drains how to find

Postby noxqus » Wed Jan 20, 2021 12:24 am

My pleasure hope it helps you.
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