dome light problem

[joe231]

Originally Posted by 19GMC63

Could you explain this Joe?
Sounds like something I should know.

Sometimes you can get a wire that might have many broken strands in it. You can check the resistance, and it will be ok, but once the circuit is under load the lack of continuous strands will create a current blockage, or corrosion in the connectors can cause the same type of issue. The way to check for a voltage drop is to put one lead of your meter on an end of the wire and the other lead at the other end of the wire, meter on DC voltage (working on a DC vehicle system), put the circuit under load (it must be under load to show the weakness). The reading on the meter tells you the potential difference. It should be close to zero, a volt or less will still operate.
Basically you are measuring how much voltage is making it through the conductor (wire)
say you are working with a 12 volt DC starter circuit, the starter will not turn the engine over, you suspect the battery cables are not up to par. so you would put your meter on the DC voltage setting, place one lead on the positive cable end at the battery, and the other lead on the positive battery cable at the starter solenoid. Then either have some one turn the key to start, or set the meter where you can see it while you turn the key to start. Say the meter reads 10.95VDC, but your battery shows 12.45VDC. then somewhere between the battery and starter you are losing 10.95VDC (you are measuring the potential difference between the meter leads, a perfect cable and connections is going to read 0VDC, no potential difference). that means that only 1.5VDC is actually making it to the starter and you either have a bad cable or a bad connection. you can do this on both the positive and negative cables as well as any other conductor you may suspect as not up to snuff.....
anytime i have a no crank condition, first check is the battery voltage, second check is the voltage drop of the cables.

Make sense Andrew?

Tony, i dunno if it will help you or not, but I was told years ago to think of electricity as water in a system of pipes, the water (electron flow) will take the path of least resistance. Many electrical components can be compared to water control pieces. A switch is like a water valve, a blocking diode is like a one way check valve, a power supply (or battery) is like a pump, a resistor is like a flow control device, and on and on. the pump (battery) can not pump water (electron flow) anywhere unless the circuit is complete.

Check out howstuffworks.com

there is generally some diagrams and animations to help visualize it.

[19GMC63]

Originally Posted by joe231

Sometimes you can get a wire that might have many broken strands in it. You can check the resistance, and it will be ok, but once the circuit is under load the lack of continuous strands will create a current blockage, or corrosion in the connectors can cause the same type of issue. The way to check fir a voltage drop is to put one lead of your meter on an end of the wire and the other lead at the other end of the wire, meter on DC voltage (working on a DC vehicle system), put the circuit under load. The reading on the meter tells you the potential difference. It should be close to zero, a volt or less will still operate.
Basically you are measuring how much voltage is making it through the conductor (wire)
say you are working with a 12 volt DC starter circuit, the starter will not turn the engine over, you suspect the battery cables are not up to par.

Thanks Joe! This will definitely be usefull... tryin' to chase some gremlins in my corvair.

Thanks for the link Mark... pretty neat idea.

[joe231]

Originally Posted by markeb01

Thanks Joe, your input is always valuable. I like to learn something new every day.

On the door switch topic, here's a link showing an easy way to do it:

http://www.persh.org/pickup/DomeLight.htm

Thanks Mark...I'm assuming you name is Mark?

Originally Posted by 19GMC63

Thanks Joe! This will definitely be usefull... tryin' to chase some gremlins in my corvair.

Thanks for the link Mark... pretty neat idea.

Sorry, i posted in the middle of my explanation, I typed half of it on my iPhone then though, what am i doing? and moved to a real keyboard at the computer

[markeb01]

[QUOTE=joe231;3595292]Thanks Mark...I'm assuming you name is Mark?

Yep, that's what I usually answer to - unless it's something worse.

[777ralph]

Thanks for digging up the door switch post Mark.
http://www.persh.org/pickup/DomeLight.htm
Doesn't get much simpler than that!
Ralph