Ford 2600 total rewire successfull (have charging question)

Totally rewired my 1976 2600 diesel today along with adding a new aftermarket gauge cluster. Wiring harness is a complete Sparex unit. Charging system is stock Motorola with external regulator and have a new fully charged 4DLT. Immediately after the rewire with key on but engine not started, the charge light was on. I started the engine, charge light still on. I let is run a few minutes, pulled off the wire at approx. 12 o'clock (field) and put it back on. Noticed a little spark when wire was connected and again when reconnected. After this, charge light went out as if the tractor was charging. Voltage was around 12.6 volts. Later, after the tractor ran 30 min or so, voltage was around 14.4 which is kind of where I would expect. Later, I noticed the charge light on again. I found the stud a little loose that the wire at about 9 or 10 o'clock connects to. I tighted it, charge light went out but voltage still only around 12.6. Is my alt charging or what is going on. Again, all the wiring is new except the POS and NEG battery cable. I just feel with my light out and charging at high 13's or low 14's everything is like it should be. But, even with the light out, 12.6 seems low and something is wrong. Please advise if you have any constructive comments or things I could try to prove this out I appreciate it.
 
12.6 volts with the engine running means it's not charging. Does the oil pressure light come on when you kill the engine with the key left on? If not, you likely blew the fuse that feeds the dash lights, and by extension, the excitation circuit for the alternator.
 
Bern, the oil pressure light is on with the key and the engine not running. It goes out as it should when the engine cranks. Everything works just as it should it just that with the engine running, charge light off I sometimes get only mid 12's voltage and other times low 14's. Everything else works perfect. I'm stumped.
 
Kinda late now that you already bought the
parts.
If I had caught you earlier I would have
recommended you convert it to a 10SI 3 wire
setup. Much cheaper to buy, eliminates the
Vreg and is very simple to rewire.
 
The tractor already had a new voltage regulator on it and I reused the original Motorola. All I bought new was the complete harness and key switch. Is there a sure way for me to confirm this Motorola is good? Or maybe it is my VR? If the alt is bad should I convert to a 10si Delco at this point?
 
I did fail to mention that my fuel gauge reading is so fluid it makes it rather useless. Is this normal? My original sender seems like it works right. Gave me about 76 ohms with the tank pretty low. I added a little fuel and it read about 65 ohms. Why does it jump around so much?
 
F = Field
R = Regulator
O = Output
G = Ground

Check the "R" terminal connections carefully, since the voltage regulator uses the voltage from this terminal as its "sense" voltage. If the connections are OK, monitor voltage at this terminal with the engine running, and compare with the voltage at the output terminal. They should be the same within 1/2 volt. If they are not, you have bad diode(s) inside the alternator.

Also, check the ground terminal on the alternator - it is a push-on type of connection. Make sure it is a snug fit. I've seen more than one issue related to this.
a211699.jpg
 
Thanks for the diagram Bern. Makes sense. The Regulator terminal stud was a little loose and I tightened it. I ran the it today for about 1.5hours. Checked voltage as soon as I cranked it - just barely below 13volts. Checked it about 45 minutes later and 1.5 hours later and it was just below 14 volts. I think all is well but I'll check the voltage at the regulator as compared to the output as you state to verify they are within a 1/2 volt to be sure. Thanks for your help.
 
What do you mean when you say "dirty contact on fuel wiper"? My instrument panel is new by the way. I get that fuel sloshing on a float means it's constantly moving but my gauge is so "fluid" it makes having a gauge useless. It goes from full to nearly empty as the fuel sloshes just nearly back and forth. It's almost like the gauge is too responsive to the change in resistance of the sender. Seems like it should vary much slower than the sender sends the output.
 

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