Connecting the Meter to the Circuit_GENERAL ELECTRICAL:ELECTRONIC SYSTEM CLASS_DN_Tech Tip.mov

We're gonna start out hooking the meter up correctly. We're gonna put the black lead into the jack on the bottom of this Fluke two thirty three that says common, and the red lead is gonna go into the jack that says volts or ohms.
Also do temperature, capacitance, and continuity test.
Now on the board well before we go to the board, let's turn the meter on. We're going to measure volts. We'll measure volts DC and we'll go ahead and turn our backlighting on so you see it better.
So we're zero point zero zero. By the way, the meter as you see sometimes fluctuate, that's called digit rattle, and that's due oftentimes to what the leads may be picking up from RFI, EMI in the building where you're working. So fluorescent lights, mercury, sodium lights, whatever. So what we're gonna do is hook up our our negative lead first to the chassis ground of the vehicle. That'll be represented by this braided ground strap on this white background.
Now Now I've got my red lead ready to go on checking anything positive or negative. We're gonna talk about both in this little segment here.
First off I notice I've got a switch in series with my power source. So there's my power source, a fuse, and then it branches out and it goes two places. So you might say these two orange wires power feeds are in parallel, one goes to these two lights, these two one hundred and ninety four bulbs in parallel, and the other orange wire goes to this brake light switch. Now if you're a detail expert out there and you recognize a brake switch off of a GM vehicle, normally the brake switch wires will be down here on this end. And when the brake pedal is depressed, that's when this pops out. But for the sake of this little setup, I've actually reversed the brake light switch contacts with the cruise control contacts which normally are open when the brake pedal is depressed.
So I actually want the bulb to come on when I push the button so I just hooked it up differently.
Actually we'll go ahead and use an ohmmeter on this switch later. You push the button in and these two contacts will be connected. Right now there's an open circuit to the bright element of this eleven fifty seven bulb, dual element bulb. When I push the button in, I will make a complete circuit between the orange wire contact and the green contact, so it'll be closing the switch here.
So right now I have it open to that brighter of the two elements in my dual element bulb. Push the button in and close the switch, and you see my eleven fifty seven bulb gets really bright. So that'd be simulating what you're doing when you push the brake pedal to make the brakes. We have basically tail lights right now, some marker lamps, and a tail light, and then we hit the brakes.
We've got brake lights.
Alright. Let's go ahead and before we do, an experiment with some problems with this vehicle, let's go ahead and see what it looks like working properly. And that's the best thing to do getting experience electrical systems or anything for that matter, always look to see what things look like when the car is working correctly.
We'll go ahead and go back to our board now.
And let's see, there's our power source of ground. Here's our power source of power. We'll go ahead and look at the meter right here where I've connected my power source into the input of the fuse. Eleven point seven three, eleven point seven four volts. This battery is definitely in need of a charge.
Alright. Now let's go ahead and move our meter lead to the first point where you can probe on the fuse.
Thirty amp fuse is a bit overkill for this little circuit, but, it'll do the job for now. Thirty amp fuse, I touch one side of the contact, eleven point seven two volts, this battery is in need of a charge.
And now we go to the other side of the fuse, and eleven point seven one.
Now you just saw me use a voltmeter to check both sides of a fuse, the feed side and the side that supplies the power into the circuit.
Well, a lot of techs, including myself, would be more in the habit of using a test light. If the light lights on both sides of the fuse, the fuse is good. The light's on one side, the source side, but not the other, the feed side, and the fuse has got it open. It's been blown. Now why would you use a meter? Well, with today's cars, more and more fuses under the hood in places where we might have water intrusion. Might not be a bad idea to see if there's corrosion at the fuse.
Now not always do you see a voltage drop. Do you see a difference in voltage between the supply side and the feed side of the fuse? But sometimes you do, so it's worth checking both sides of the fuses to make sure we have the same voltage. Tells you you got a good fuse, it tells you I don't have eleven point seven on one side of the fuse, and on the source side I've got, we'll say, nine volts that would tell you how to drop a voltage drop, voltage being used by the fuse through a bad connection, a resistance in the in the actual spade t