Amp light question

I put a single wire alternator on my farmall 504. I connected the arm wire and the batt wire at the regulator and connected the arm wire to the output of the alternator. The charge is only 12.3 v and when I shut off the tractor the amp light comes on. The alternator is used that I got in a box when I bought a tractor so no telling on how good it is. The amp light is off when the tractor is running though. What could be wrong?

Thanks.

When you connected the arm and battery wire, did you remove them from the regulator? As long as they are spliced together securely, and disconnected from the old regulator, that will work. At the same time, all the other wires connected to the regulator, or that were connected to the generator, need to be disconnected and insulated, or traced to their origin and removed.

The 12.3 volt reading is too low. Some of the old one wire alternators required a high RPM to initiate charging. With the engine running at full governed RPM, check the voltage across the battery. It should be up around 14.5 volts.

Next check the voltage at the post on the back of the alternator. It should be close to the same as the battery voltage, just slightly higher. If the voltage at the alternator is higher, up around 15v, and the battery voltage is low, 12v or so, there is a bad connection between the alternator and the battery.

If both readings are low, there is a problem with the alternator, or the belt is slipping. Be sure the belt and pulley are compatible, properly aligned, and the belt is tight. If the alternator proves to be faulty, it can probably be repaired at an alternator/starter shop cheaper than replacing it.

The ARM/GEN wire is still connected to the gen light wire, so you are getting a back feed through the gen light to the ign circuit, causing the light to be on when the tractor is shut off.. Find the GEN light wire, it should be a small wire connected to the GEN/ARM wire in the original harness at the old regulator. Remove it from the ARM/GEN wire. Buy a GM alternator repair plug kit from your auto parts store to plug into the "1 wire" alternator and connect the original little gen light wire to the #1 (usually a small white wire in the alt plug). This will give you a correctly functioning gen light and will excite the alternator at lower rpm. A real win win deal, as you get the light working correctly and get a quicker exciting alternator.

Just to add another thought, you say the 1 wire alt is used. On the chance it is not a 1 wire, but a 3 wire alternator, connect the #2 alt plug wire using a ring terminal (usually a heavy red wire in the alt plug)to the alternators BAT stud along with the other wire from the tractor. This will then be correctly wired for either a 1 or 3 wire alternator should this be a 3 wire or if you ever need to replace the alternator.

First of all I would ONLY have connected the old BAT wire to the alternators output stud as it wires to the ammeter (if it had one) or the hot ungrounded battery post eventually, often where the big battery cable wires to a starter switch or solenoid. The alternators output has to get to the battery somewhere even if via an ammeter if it had one to charge it.

2) I would not use the old ARM wire whatsoever as it used to attach to the gennys ARM post.

3) I would have upgraded the wire from alternators output to battery or ammeter with at least 10 or even 8 gauge.

4) If it had an old idiot light on a genny and Voltage Regulator system it wired from BAT on VR over to GEN/ARM on VR. If it was a 3 wire alternator I would have re wired it into the excitation circuit but if its only a one wire alternator I wouldn't leave it as you have it (but alternator still has to wire to battery remember) as it may be wrong BUT I CANY SAY NOT BEING THERE. To be safe for now disconnect it until you know how to wire it right as if its for the old genny and VR it may be wrong and the one wire alternator should NOT need external excitation wiring.

Basically with a one wire alternator it needs the correct and a good frame ground of course (usually NEG ground unless its a special, IS YOUR BATTERY NEG GROUND??????), then all it does is its output gets to the battery and it charges it. If its working check battery voltage tractor not running and if charged it is around 12.6 volts. Then start her up and once enough RPM is reached so it self excites, battery voltage should rise to al least 13 and up to 14 + subject to RPM and battery state and alternator and its voltage regulation circuitry.

If a one wire doesn't get enough RPM it doesn't excite so you need the right pulleys and RPM and a good tight belt and its output wired to the battery THEN AT SUFFICIENT RPM IT SHOULD PUMP AMPS INTO THE BATTERY AND ITS VOLTAGE WILL RISE

HOPE YOU HAVE CORRECT GROUND

Many auto shops will bench test an alternator for free, have that done ASAP,,,,,,insure ground,,,,,,,,,wire output to battery or ammeter, ,,,,,,,,,,,,,check battery voltage not running (12.6) ,,,,,,,,,,,,,start her up and at enough RPM it should engage and raise battery voltage (13 to 14+)

John T

thanks guys. I will check those things. Appreciate the help!