12V conversion not starting/charging

My recent aquisition, a W-9, was bought with a 12V conversion. It was starting/charging when I brought it home. I let it set a couple days and then it wouldn't start. Traced the problem to no voltage to the ignition switch which is fed directly from the #1 terminal on the Delco alternator. Ended up running a jumper wire from the battery to the coil resistor to get her started. Then I noticed it wasn't charging.

From the wiring diagram for 12V conversions, I do not have a warning light wired in. As noted above, the ignition switch is wired in to the #1 terminal. It does NOT pull its voltage from the ammeter. I'll have to check the rest of the alternator wiring, but I suppose it's possible the alternator suddenly quit on me. The wiring, though, certainly doesn't jive with Bob's diagram.

Chris B.

I just did some more thinking, and I believe I must have popped a wire loose from the ignition switch. I pulled the fuel tank and reinstalled it, so there's a good chance I yanked something out. Still, my conversion does not have the lamp wired in, and I'm betting it's rather important.

Chris B.

For one thing, the internally regulated GM 10 SI Alternator (if thats what you have????) should get its excitation voltage (to make it start charging) from the ignition switches IGN OUTPUT terminal which is hot ONLY after the switch is turned ON via a wire from there to the alternators lil side No 1 terminal.

I prefer a 10 ohm current limiting safety resistor in that circuit after the switches IGN output and before the alternators No 1 terminal which also prevents backfeed ignition run on after ign switch is turned OFF, although an idiot light can serve the same purpose and many use a diode there which also works to prevent backfeed run on. NOTE a diode must be wired in correct polarity to work !!!!!!!!

The ignition switches BAT input terminal should alwayssssssssss be hot as its fed hot battery voltage off the ammeteres load terminal or the LOAD terminal if 4 terminal VR's are used. Thats NOT where the alternator is fed its excitation voltage to its No 1 terminal since thats alwayssssssss hot. The alternator is supposed to be excited when the ignition switch is turned on so thats why the switches IGN Output terminal is used to excite the alternator.

The alternator doesnt feed the ignition switch its operating voltage, the switch (when ON) feeds voltage to the alternator to excite it. The switch gets its hot battery input voltage (on its BAT input terminal) from the ammeter.

Those alternators require negative ground you know!!!!!!!!! reverse may fry them !!!!!!!!!

Insure shes wired so the switches BAT INPUT terminal is always fed hot voltage like from the ammeter while its IGN OUTPUT terminal (hot ONLY when switched ON) feeds the ballast (if used) and coil plus the same terminal can feed/excite the alternators lil No 1 terminal via a series 10 ohm safety current limiting resistor or an idiot light or a diode to prevent backfeed causing run on even after switch is OFF

The alternators other lil side No 2 terminal jumps to its big rear output stud/lug.

WIRE IT PER BOB M DIAGRAMS AND INSURE SHES AT NEG GROUND

John T

An idiot light wired (between switches IGN output and alternators lil side No 1 terminal) in can prevent backfeed ignition run on so the tractor dont keep runnign even after the ign switch is turned OFF

YES ITS IMPORTANT

As posted above I prefer an idiot light or a 10 ohm resistor over a diode to prevent run on although either will work if wired correct

Check for BAT INPUT voltage getting to the switch fed off the ammeter cuz if its not that can prevent the ignition from working and prevent charging !!!!!!!

I think you just lost power to the switches input, get a test light n go to work !!!! Likely a loose or pulled off hot feed wire to the switch

John T

Just thinking, but even if I knocked a wire loose, the coil was still wired to one side of the ignition switch and the alternator to the other side. This is not at all properly wired. Add that to the missing idiot light, and I guess I should be surprised it ever worked at all.

I will take a good look at it tomorrow.

Chris B.

John, If a person were to utilize a simple key switch for automotive use (with Off--ACC--Run---Start) and wired it so that the Start position would be used to excite the delco #1 terminal, Not start the engine, It would be a pretty simple way of making the tractor more secure from casual operation (Key) and to start it charging. What do you think, JimN

I got the charging and starting all squared away. I did, indeed, knock a wire loose. And after I figured out the toggle switch (4 prongs, some hot some not), and rewired it per Bob's diagram, everything worked perfect.

Thanks for the inspiration John.

Chris B.

Hey Jim, You mean use the momentary Start/Crank terminal off one of those generic switches to excite the alternator I take it?? The one thats hot ONLY while cranking??

Im not sure how good that would be (if thats your intent) cuz when cranking 1) The battery voltage is reduced 2) The RPM is slow and the alternator may not turn fast enough to ever kick itslef into self excitation.

I dont understand how you mean to make the engine crank withiout use of the momentary start/crank terminal BUTTTTTTT of course thats for a solenoid type of starter arrangement instead of a mechanical push start switch..

I see the ignition terminal (one thats hot to feed coil when ON) as the better source cuz it stays hot to excite the alternator during and until its RPM raises sufficient so shes self excited..... Im afraid if you only applied the external excitation (while cranking at slow RPM) while cranking once it switched off the alternator wouldnt ever become excited unless maybe after a high RPM???????

I know you know this stuff as well and better then myself so Im not sure were on the same page here or that I understand your question??????



John T

Idea is different.
Turn the switch to run crank (hand crank would also do) with pull or push rod mechanical starter switch. After it is running, momentarily turn it to start to excite the alt! Jim

I changed my SC to 12 volt last year and it works great. Just followed Bob's diagrams. I like the idot light myself, lets you see excatly whats going on. If not charging or stops charging you can see it right away, don't get the suprise of a dead battery when you go to start the tractor next time.