good morning everyone, I have a 61 gmc 1500, 305 v6 , the generator took a cleaveland steamer and I am switching to an alt today, some of the diagrams show no diode and some do, is it mandatory or not? I have a three wire gm alt and believe I have to. And also who even sells them, radio shack here just closed and the parts stores are utterly useless , any help would be greatly appreciated
Found out myself when the car wouldn't shut off! Try Rebel Wire(sp?) here on the HAMB. Painless directed me to Radio Shack back then.
The short answer is "probably not". Running the wire that has a diode into the idiot light circuit is usually enough to kill it when you turn the key. The easier answer is a diode just allows flow of current in one direction so it's what I would consider the right way to do it.
You should already have a GEN light with two wires on it. One comes from the Ign side of the ignition switch and the other goes to the #1 terminal on the alternator. Serves the purposes of exciting the regulator in the alternator and indicating whether or not the alternator is charging.
If you have an ignition switch with an ACC terminal you can run the alternator excite wire to the ACC terminal instead of the ON terminal. When switched ON the ACC terminal will excite the alternator and when switched off the ACC terminal is isolated from the ON terminal so you get no feedback. No diode needed.
Cheapest way I know is get a side marker lamp socket and about 6" of the pigtail from a junk car [194 bulb]. One wire to #1 term on alt., other wire to almost anything hot with key on [ig,dist bat,12 v. coil etc.]will not feed back through light bulb and car will shut down when key is turned off.
The acc terminal works well most of the time the ignition resister will knock down the voltage enough to stop run on. If you pick up the power for the alternator from the coil is a sure thing to get run on with out a diode.
Thanks everyone for the help. Turns out we had one wire alt here so im gonna run that, and i was figuring on just wiring it, thrn running it till its charged the batt then doing a draw test to make sure and if i have no draw then I would think i dont need a diode, but i like the acc switch wiring idea as well, ill keep everyone posted, thanks again
One wire alternators self excite, so no diode needed. However you will have to rev the engine a bit for the 1 wire to start charging.
I realize you've already solved your problem but for those who may read this::: I like to use an idiot light wired into the exciter circuit so I'll know if the battery is charging but I've bought cars with a 3 wire alternator and no exciter wire going to it...a bare plug with nothing plugged into it.. Even the 3 wire alternators will charge if you start the engine and rev it to about 2000-2500 RPMs. Do it at night and you'll see the headlights brighten when the alternator begins to charge. Only down side is when you have to go to work at 4 am and your hot rod has no/loud mufflers. You fire off that motor and after the idle smooths out, you blip the throttle to get the alternator charging. Neighbors may think you're deliberately trying to piss 'em off.
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