ok i included a schematic of the charging system and ill give you a brief run through.

first off, basic theory, yay i know, anyway electricity takes the path of least resistance. Also the more current going through something like a light the hotter is gets and the hotter it gets the more resistance it creates.

now onto the way the light in the car works. please note it's 2AM and im tired so i may oops a few things but ill try not to. so the power coming from the alternator has a wire that goes to the instrument cluster. then it Y's off, left is a resister of unknown ohms or K ohms. right is a light bulb. going back to the path of least resistance now. when low power the light creates the least resistance, so the power go through that making it light up, when the power goes up high enough. it creates more resistance through the light than the resistor. so the power again takes the path of least resistance only this time the resistor has a lower measure of resistance (measured in ohms or K ohms) so the light then goes out and the resister provides its path the ground. which is why IF the charging system is infact fine your light can still pop on. because resistors do wear out.

 

2 am? I got 3:15 here


I give you props for digging up a diagram I haven't been to the shop since Wednesday to find one. lol.

But to me, it seems as if the only way the light will turn on, is if the Alt. quits producing voltage (or produces less than battery voltage(failing diode(s)?)), it will become the ground for the light...?

I'm probably missing something simple, but I blame it on not being able to sleep




~EDIT~ just realized my mistake, got it...

 

it's not so much the voltage as the amperage. think of it this way, car stereo amps need thick wires to handle the amps they pull, to small and it will over heat and melt. heat also creates resistance. same theory applies to the light and resistor. the resistor has a set resistance level, the light does not. the more amps the alternator puts out the higher the resistance the light gains until it gets the the point where the light has a higher resistance than the resistor. and since electricity takes the path of least resistance when the alt is pumping out 90 amps the light is major resistance and the resistor is small so the electricity skips the light (oh yeah sorry forgot to point out the sqwigily line next to the light is a resistor). when the alt is not pumping amps the resistor is higher resistance than the light so the electricity skips the resistor and goes through the light illuminating it.

when resistors fail more than likely they fail in a way to produce more resistance so the light has a hard time creating more resistance than the resistor so it sometimes can illuminate under proper amperage load from the alt.

edit: lol thats good that you got it cause this response probably would have confused u more than help

 

Actually I perfectly understand a wiring diagram Just got done with the Electrical automotive class for ASE...

for SOME reason unknown to me, I was thinking(3 am) that the current was flowing the wrong direction.

 

Man its been one of those weeks now yesterday I got a call that the car won't start cranks over but won't stay running i am thinking that its the IAC hope it is, just put smug pump in it new brakes all around now I was trying to get this battery thing fixed now this plus 20 inches of snow, ok thanks for help going to have to see if I get can car dug out and to my house so I can pulled it in my garage and work on it some more. Thank for all the help

 

nice im hoping to take my ASE for light gas engines in spring

 

Thanks for help ,as luck would have it I could not get car to fire today so I bit the bullet called Triple a for my free towing and its at the ford dealer, there going to check it out tell me whats wrong and give me the damage estimate, I will let you know how I make out , I think I sit down when I get the call, LOL. Thanks again

 

Follow up ,well got a call from the dealer today and they said it is infact a bad alternator, I guess I am done getting things tested at advance, any how I said to the service person how does a bad alternator cause me to have a start problem, because car was still cranking for me, but he told me they had to jump it to start, and he tells me a bad alternator can indeed cause start problems, I ask him just to check everything out onced they get it running to make sure they are no other issues. Merry Xmas To all

 

yeah we (by that i mean me and a friend) had a alternator that didn't show up bad until we got it up there in the car and had them hook up the mobile cart to it. showed fine under no load but with the car pulling a load on it then it failed.

 

Did you ever try to start it and then rev it in front of a wall at night? The voltage regulator might have been the only problem, causing the output to drop when the engine is under a load.