The Stovebolt Site Forums The Shop Area The Electrical Bay Generator light on when ignition is off

Bear with me as I am fixing someone else's wiring job!
1960 GMC 1000 ,12 volt system, 305A V6
They put a internal regulated alternator on.
When the truck is off, key out, the generator light on the dash is on. Turn the key to ignition on, and it goes out. Start and run, it's still off. I think someone wired it wrong (obviously!) I did test the alternator, and it is hot on the one side when off, but I think that is because it runs the lead to the battery to recharge it. Does a wire supply power to the alternator to "excite " the field when running? (I am thinking they wired that hot, not via a ignition feed) How does the gen light figure in this , so it knows when to turn off/on?
I appreciate the input,as I want to fix things so they are right! Meanwhile, thank goodness for a battery cut off switch!

Longhaul,

It sounds like you have it figured out. A wire should run from a key switched terminal, through the GEN light and then to the #1 terminal of DA plug.

That tab on the DA plug should only show voltage when the key is ON, not when it is off. When you turn the key ON, the GEN light is powered and finds a ground through the internal regulator. When the truck starts, that terminal now generates voltage, the ground is lost and the GEN light goes out.

I think this is how it works.

Stuart

I have a problem like that, I used a relay from the switched ign. wire to operate a relay to power my hei, problem is, it won't kill the engine when I turn off the switch. Voltage is in a loop from somewhere, I leave my utility spotlight on which makes it die when I turn off the ign. Tested the ign wire, it goes dead when the switch is turned off and the relay circuit is unhooked, tried 3 different relays, cut the balast on one relay loose to see if it was holding a charge. Funny thing

Some relays trickle a little current even when open(off)> Use an ohmmeter to test it. I suspect mine is just wired [censored] backwards, as the guy I bought it off of, in hindsight ,throughout the buying process I never saw him without a beer in his hand,ever.You ought to see the repairs to the parking brake cables,make you laugh.Think hardware store cable and mini"u"bolt clamps...

Update. Totally backwards wiring job. I am going to redo as soon as it stops raining.

One of the terminals needs a constant 12V, usually provided by a jumper to the alternator output terminal. The other one provides the ground for the No Charge light when the alternator is not turning. During correct operation, the light should go out as soon as the alternator begins charging. Depending on the design of the internal regulator, it might be necessary to rev the alternator above idle speed once to kick in the charging current. Later model regulators will begin charging at idle speed.

I don't have a schematic handy at the moment to tell which terminal gets the constant 12 volts, but you've got a 50% chance of doing it right the first time. The rectifier eliminates the need for an isolation relay on the main charging lead- - -just connect it straight to the + terminal at either the battery post or the starter solenoid.
Jerry

The previous owner tapped the dash warning light to the hot wire coming off of the alternator ! The field feed wire didn't exist! I put in a new alt. and hooked it up properly, with all new wires! I found they also hooked the oil light up by wrapping wire from the sending unit up around the steering column and then folded a hook on the bared end, put that to the folded hook of the wire going to the dash. They did cover it with electrical tape at least!