Automotive, Electrical Diagnosis

Find Automotive Short To Ground Training

In this lesson, you will learn how to find automotive short to ground and what the meter readings are telling you. When testing for a short, never apply power to the ohm side of the meter because you will burn up the meter. All ohm readings are done with the power off, battery disconnected if necessary. In this case we assume the fuse is blown. All power is off and no current is flowing. Remove blown fuse. Set your meter to ohms scale. Place your positive meter lead on the positive side of the load and the negative lead on the negative side of the load. In my example the load is a lamp. You should be reading the ohm value of the lamp filament of 10-15 ohms. We read 10.8 ohms. Next remove the load (lamp) and measure the resistance of the load by itself. We still have 10.8 ohms so we know the load is ok and not causing the short. Now leave the load removed and place your leads across the positive and negative side of the socket. The reading is still .2 ohms. This reading is actually the resistance in the leads of the meter itself. If your meter is at zero on the ohm scale when turned on, touch the black and red meter leads together and note the reading. This reading is the actual resistance in you meter leads. You can set your meter to reflect this or just subtract the lead resistance from total resistance. Just an FYI.

Next place the negative meter lead on the battery ground post and the positive meter lead on the cold side of the fuse holder. Your meter is still set on the ohms scale. We read .8 ohms. Remember this important tip. When you place the negative meter lead on the negative battery post and the positive lead on the cold side of the fuse holder, you should ALWAYS read OL (outer Limit) or 1 depending on your meter. Any other reading is a red flag that there is a short. Simple as that!!! Now you have to find automotive short to ground. Start disconnecting, closing switches etc. until you get that correct reading of OL or 1. Once you find that reading, you now know the fault is between those 2 points. This is exactly how to find short to ground. This process works for any short. That’s all there is to it!!

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