How can a person get better at reading wiring diagrams

Oh it's a private message. Must be for Noah

Jay2034 wrote: Hey what's going on Paul. Usually I always email u but thank u for taking ur time for the PM. But what's a PM? And how do I check it. Lol. I'm so serious

I'm so sorry Jay2034 that was meant for pole71
A PM is a private message and you'll find them under your profile image

Jay2034 wrote: Thank u once again guys. So what bout the fuse 7.5 that inside the box that only has power on one pin and the other has 1.2 volts. How can I attack that.

This is without the fuse inserted, correct? Put a fuse in it. Set a multi-meter to Milli-volts DC (MV). Using the two test points of the fuse, Measure the voltage drop across the fuse. Is there one?

Ok brother. So Monday I will do that. So if there is a voltage which more likely will be what can I do after that. I haven't used that type of method. Is this to locate a short in a wire. Because with the fuse out one pin had 12 volts and the other pin had 1.2 volts in the fuse box

I wouldn't worry about the 1.2v, at this point. That ties in with multiple other modules. That is, likely, feedback voltage that will be overtaken by the 12v when the fuse is inserted. I could be wrong, and it would take someone with a lot more knowledge in circuit design, than I possess, to explain it.

I believe, this is the power source for some sort of communication between the window motors and the GCMU. I could be wrong about that, too.

What I am sure of is that, if there is current flow through that fuse, you will see a voltage drop. That is my concern, right now.

This is a handy chart that will convert the milli-volt reading you get, into a Mill-amp value for the different fuse types.



You can operate the windows and watch the amperage.

Pole71 honestly brother if I do have current flow what approach can I take. Because with the fuse in and I touched the pins there were 0 volts on each pins with it in. I'm just asking cause when it does come Monday I know where to start at already. Do I start unplugging stuff. I'm just confused brother hope u understand. I really appreciate the help

Just to make sure we are on the same page, when you say:

Because with the fuse in and I touched the pins there were 0 volts on each pins with it in

Do you have the negative test lead touching a ground? (you should read 12v on both test points) Or, are you measuring like this:



If you are reading 0 volts, measuring like the picture, this means you have 0 voltage drop...no current flow.
If you are measuring like the picture and get a reading, other than zero, this is a voltage drop across the fuse. This indicates current flow. Compare this reading to the chart.

Yeah my test lead to a known good ground. In this case to verify I used the ground from my power probe just to be sure I had a good ground. With the negative lead on ground and positive touching each pin on the fuse with it in the box is zero volts. Now with the fuse out it's 12 on pin and 1.2 on the other. That's where I was forced to stop cause now I needed advice as to how to attack that approach because I never encountered that. Other times it's just a blown fuse and pop one in and that's it. Not in this case my friend.

Jay2034 wrote: if I do have current flow what approach can I take. Because with the fuse in and I touched the pins there were 0 volts on each pins with it in. I'm just asking cause when it does come Monday I know where to start at already. Do I start unplugging stuff.

I feel like we are getting, a little, off track. Measuring a voltage drop across a fuse is a method better used for identifying which circuit is responsible for a parasitic draw. Very small amounts of current. I mentioned it in this application, simply, to give you an easy way to make a comparison. I am curious to see if there is a base current draw.

We are looking for EXCESSIVE current flow. The fuse protecting that circuit is rated at 7.5 amps. If it was blown, it exceeded that. To measure this kind of amperage, the multi-meter will, probably, need to be set on VOLTS DC, not MILLI-volts. If we were looking for a parasitic draw, we would start unplugging things, and look for the voltage drop to go away. We are not looking for a parasitic draw. Instead of unplugging things, you need to do just the opposite. Turn them on. Windows up. Windows down. Wiggle the wiring harness. Flex the connectors. Bounce up and down on the care. Open and shut the door. All the while, monitoring the current flow/voltage drop. Watch for spikes. If you can MAKE the fuse blow, you're getting close.

Jay2034 wrote: Yeah my test lead to a known good ground. In this case to verify I used the ground from my power probe just to be sure I had a good ground. With the negative lead on ground and positive touching each pin on the fuse with it in the box is zero volts.

That changes things, a bit. Do you have an incandescent test light?

But what I did is put the fuse slightly in and I can get power to the window switch with the 12 volts but when I put the fuse all the way in it pulls it straight to ground. Something is pulling it to ground. But like I said before this lady has had this issue for some time and has a shop I guess she brings it too when she accident puts the window down and they can bring it back up. But what I don't know is that if they grounded the wrong wire or put 12 volts on a wrong wire before they figured to unplug the motor connector and just shoot power straight at the motor. I don't know. It's all up in the air for me right now as I'm thinking how to attack this.

Yeah test light of course.

When you take the fuse out, the side you measure the 12v on, does it light the test light as bright as the positive battery post does? (Test light connected to battery Negative)

With the fuse pushed all the way in, you said you read 0 volts? You think it is being pulled to ground? With the test light connected to battery Positive, touch the fuse test points. Does it light the test light?

Will do this when the lady comes in on Monday. What exactly are u trying to find out if it lights or doesn't light? Because if test light connected to to battery negative test light should light when voltage is present . Maybe I'm over thinking and need to just chill out? I just be getting these what if"s and why's.

I'm starting to think you have a voltage drop BEFORE the fuse. Reading 12 volts on a digital meter, doesn't mean that it can carry a load. If you have a corroded connection inside the power distribution box, you can read 12 volts when there is nothing using that 12 volts. But, when you introduce a load (test light bulb) the voltage will drop. That is why I asked about the brightness of the test light. If there is a corroded/bad connection that causes a voltage drop, the light will not be as bright as it would be without a voltage drop. Depending on how bad the drop is, it might not light, at all. Here is a great video for explaining this.

For some reason, the video is not starting at the beginning.

Will see this video right now again and again. Thank u sir. But I'm thinking this fuse box is bad inside. How can I have 12 volts on one pin with fuse out and 1.2 on the next. So u want me to use the test light and see if it lights and how bright if it lights at all. Thank u. After my readings depending on the results what would I do after?

Jay2034 wrote: I'm thinking this fuse box is bad inside.

I am thinking the same thing. If it turns out that you are losing voltage inside the box, before the fuse, my next step would be to take the box apart (disconnecting the battery, of course) and see if I could fix the connection.

Jay2034 wrote: Hey what's going on guys. I'm new to this forum and been a member of the premium channel. But if anybody has suggestions for me or has done it before or resources I can go to to get better at reading wiring diagrams. I have 4 months of this engine diagnostics and honestly it's going pretty well at the shop. But the shop is very limited in resources as far as scope equipment or guys in the shop with knowledge. We have alldata but I see michell has better diagrams when Paul uses them. But this 04 bmw wiring diagrams for the window power switch is really tough to dissect with a bunch of wires it has on it and really nailing which wire to send 12 volts or ground it. Bosses don't understand that. They just say how can't u figure out how to put the window up. Mind u I'm the youngest guy in the shop and the guys with 30 or 40 years of experience can't figure it out either. It's just frustrating with the pressure and the lack of resource we have there and really no one to turn to as far as other techs because they are just parts changers and throw parts and after three parts thrown at it then the fourth one is the problem. And the bosses don't care because they see money coming in but it is biting them in the butt with all the comebacks these guys are having and then the boss throws it at me and expects me to figure it out. It's just really frustrating and I don't mind the challenge but if anybody knows of resources,books, training courses, or something i would greatly appreciate it. I'm studying everyday even when I come home from work. Paul is the best teacher I've had and really grateful to be part of his premium channel. Thank u guys. By the way I live in new jersey just in case if anybody knows anything in my area. And who knows maybe I can meet some of u guys if ur from around here and become good friends and help each other out when we have problems. Thank u and God bless all of u

It's easy for them to sit in there chair behind her desk come out every once in awhile and go what the fuck is taking so long pardon my French but I know exactly how you feel that's pretty typical with a lot of bosses they soon lose the memory of what it's like to be under the gun and trying to figure stuff out with little or no help

Sent from my XT1575 using Tapatalk