The Stovebolt Site Forums The Shop Area The Electrical Bay generator light basics

i have a problem on my 63, well several actually, but something with the keeping a charge. i have had the alt tested several times, it is good. i have a new voltage regulator that is a couple of years old. i have wrestled and wrestled tryng to see why the battery goes down after a while.
i bought a new bulb for the gen light and it still does not come on. i checked and both the pink wire and the brown wire have 12 volts going to them with the key on. the pink wire goes to the socket part and the brown goes to bulb nub. how does this actually work to turn on the bulb? the brown wire goes to horn relay- i think and pink wire goes thru key- i think. can anyone tell me the basics? what is supposed to be happening here to turn on and off bulb?

I'd have to look at your specific wiring diagram, but in general, voltage is supplied to the light when the ignition switch is turned on, and it grounds itself through a circuit in the regulator as long as the alternator is not producing current. Once the voltage from the alternator rises to match or exceed battery voltage, equal voltage is applied to both wires, and the light goes out for lack of a ground.

It sounds like you might have a leaky diode in the alternator which allows a trickl drain on the battery when the vehicle sits for a while. Try disconnecting the heavy charge lead at the back of the alternator the next time you park the vehicle, and see if the parasitic drain goes away.

It's possible for an alternator to keep the battery charged during periods of light load even with one or two bad diodes, so a bench test by the average parts store guy might not find the problem.
Jerry

thanks for the info hotrod lincoln. i checked on my 64 whick is working as it should and just one wire is hot at the bulb socket so looks like there is a problem with the wiring or voltage reg. you may be correct on the leaky diode, but i don't think it is charging at all. i can drive this truck 5 times or so before it's drained too low, but it's prob just running off the battery.
this truck always has what the battery has, voltage wise- 12.5 volts, at the horn relay, but my 64 which is functioning as should is 14 volts at the horn relay with the engine running.

I assume you've got the 4-contact square-housing regulator and the alternator with two blade connectors in the back of the housing? The alternator should be able to be excited by applying battery voltage to the right side blade terminal, looking at the back of the alternator. This terminal should have a wire attached to it from the "F" terminal at the regulator, the far left connector when looking at the 4 terminals straight on.

The terminals on the regulator are marked "F", "2", "3", and "4". "F" should be self-explanatory. "2" connects to the other blade terminal at the back of the alternator. "3" is a constant 12 volt connection which bypasses the ignition switch. "4" is the ground wire for the idiot light. The other side of the idiot light gets 12 volts when the ignition switch is turned on. Some applications also have a circuit from the ground side of the idiot light connected to the "accessory" terminal of the ignition switch with a resistor inline. The simple fix is to swap to a 10SI alternator with an internal regulator. Good luck!
Jerry

thank you for the good explination. i think i will print this off so i can keep it. i have a little trouble understanding the manual on wiring, i just don't have the general knowledge there.
I DID FIND THE AT LEAST ONE OF THE PROBLEMS! the spade rerminal going from the cab to the engine bay for the brown wire had broke and some previous owner and crimped the brown wire in another terminal. so after i did away with the broke terminal and got the wire in propper location- the charging idiot light is working now. and it shows the charging system is working! this wire from the voltage reg was charging something in the wiring harness! that may have been causing part of the problem. so i will give it a little time and see how it does. i am just so happy i got this part figured out. thank you for all the help. i never thought about checking that. i don't know how he crimped that wire in that 5 spade terminal anyway. i actually had to cut part of it away to replace it.

thank you again, Mr Hotrod Lincoln! the only thing i like better than learning somthing, is fixing something. i drove the truck today and it is now charging correctly and the gen light is working too! i am going to start driving this truck more now that the charging is fixed, instead of always jumping in my 64. thanks again.

"I love it when a plan comes together!" Usually, electrical problems can be solved by breaking things down into individual circuits. It really gets overwhelming when someone tries to look at the entire circuit at once. In the 50+ years I've been fixing electrical problems and teaching the subject, I've found that it takes a special talent for someone to visualize what's going on in a wire. Since it's not possible to watch the electrons flowing, it takes a pretty good ability for abstract thinking. Some folks have a lot more trouble than others doing that!
Jerry