How To Use a Multimeter – Test Car's Ground – Video 3

How To Use a Multimeter – Test Car's Ground – Video 3

July 12, 2019 28 By Bernardo Ryan



hey this Delta fats here and in this video I will show you how to use a multimeter to test the ground on a vehicle now in my last video I showed you how to test the voltage on a vehicle's wiring and to do a proper measurement of the voltage your ground has to be good has to be a good solid ground back to your battery if you don't have a good solid ground the voltage measurement you have is not going to be good also if you are say installing an aftermarket amplifier which requires a lot of current draw you need to make sure the grounding point for the amplifier is solidly good okay otherwise you're going to have what they call a grounding loop now as I mentioned in my last video your car is made of steel and steel is a conductor but it's not the best conductor so what happened is that when they manufacture the vehicle they have well points so different panels are welded together so there are spots on the metal sheet metal that is welded together but sometimes those well does not make a good contact between one piece of metal to the other so you got to make sure that if you're going to be checking or using that piece of metal as your ground to measuring voltage you got to make sure that grounding point is good I remember many years ago I did a following install where I had to install a relay to provide power for the fog light and the relay also required a ground so I tapped the ground off one of the sheet metal on the front of the vehicle and when I turned on the fog light to test it the relay started buzzing really loud and immediately I knew there was something wrong so I broke out the multimeter tested that ground wire to where I tapped off on the sheet metal and I found out that there was a lot of resistance between the sheet metal and the ground on the battery so that shows you that you can't just visually assume that because it's a piece of metal here here or here that it is going to be a solid ground back to the battery another thing you'll notice is that if you take your car to get an amplifier installed at audio shop let's say that our amp is installed in the trunk of the vehicle and one thing they'll do is that to get a proper ground if they cannot find a factory ground is that they will actually tap a ground onto the sheet metal and they'll sand it down with a sander to make sure all the paint's removed then they take the multimeter test to make sure that grounding point is good and to do that test what you need to do on a multimeter is set it to this ohm measurement it measures resistance okay and on this other multimeter there's also the same symbol here okay this will measure your resistance or the ohm on the circuit so how you would do that is if you take your positive and negative probe okay so the way this works is that when you have this set to measure resistance anything between the two probe will give you a reading on the multimeter on what kind of resistance it is so if I was to short out these two probes this is a direct short so there should be no resistance between the two as you can see it might give you like Oh point six point seven or one point zero that tells you that this is a complete circuit okay there's no break there's no resistance between the two probes over here I will take one of the probe put it into the negative terminal and I'll just quickly show you if I take this other probe and stick it on to one of the grounding points on the engine say over here point three or say if I connected to one of the bolts on the shock tower here 1.8 or let's say over here on the fender there's another bolt here on point 5 or somewhere on the engine block and to touch the engine block here 0.0 very good this shows you that depending on where you connect to there is gonna be a slight difference and you got to make sure that when you're testing the continuity from one probe to the other probe you got to make sure there's no huge amount of resistance between it or let's say if you're testing a wire that's inside the vehicle to see if it's a ground a good ground then you use a piercing probe like I showed you in my last video and unplug one of the probe wires plug this one in here and then you can test the continuty between this piercing probe which is connected to the wire that you're testing and a grounding point so you can check what kind of resistance it has let me show you some example of how the manufacturer use the cars chassis as a ground to connect their electrical so if I put my camera here you see those two bolts right there those two bolts are connected to the driver side fender and that is a grounding point they're using for the electrical on the passenger side you'll find three more bolts right there third use as a grounding point for the cars electrical over here on the ECU you'll see there is a bolt right over here this is actually the grounding point for the ECU itself that is tied to the chassis so here's another test I can do with a multimeter using the resistance measurement and this fuse here is supplying power to my amplifier and this wire through this views is connected to the battery terminal positive battery terminal so in my last video I was measuring between the negative and this point on the fuse to check for voltage but let's say if I want to check the continuty of this piece of wire from here all the way back to the battery terminal the positive terminal what I can do is put one probe on the battery terminal compositive and let's stick this end over here on the other end of the fuse as you can see zero zero zero point one so this tells me that the continuity from the battery terminal all the way to this point on a fuse is good you can also use it to test a speaker because a speaker in essence is a big resistor it's a coil of wire inside and I have here a car tweeter which is right at a 4 ohm most car speakers are four ohm and what you want to do is disconnect the speaker from the car put your probe on the two terminal and you see on a multimeter now measures three point nine four ohm so we know that's good if let's say you don't get any measurement on these terminals then you typically know that the speaker is blown because there's no current passing through the coil so I hope you found this video helpful and hopefully it will help you with troubleshooting any drowning problem or if you're doing any type of installs that require a good ground you will know how to use a multimeter to check that and verify that anyways you need questions leave a comment below and if you liked the video please subscribe thank you for watching