4320 not charging

I took the alternator to the dealer to get it tested and it was putting out 13.6 volts. They were telling me that if the light on the dash does not function the system will not charge. Is this correct? I have main power and keyed power at alternator. The bulb was burned out. Thanks
 
Yes, that advice certainly can be correct. Replace the bulb and all should work fine again. The bulb current develops 'sense' voltage, without it the alternator has power to work but doesn't know it should. Voltage difference between Key power and sense voltage will put the alternator to work. When they are near same causing the light to go out, the voltage regulator turns down the charge to almost nothing.
 
Don't be surprised if the light doesn't go completely out, some will barely glow and is of no concern.
 
The number 2 terminal is the voltage sensor. It can be hooked to the alternator output terminal or someplace nearer the battery. The latter placement will correct slight voltage drops in the output circuit. The number 1 terminal hooked to the light is the"excite" terminal it wakes up the voltage regulator. The light goes out when you have fairly equal voltage on both sides of it. The alternator does NOT stop charging when the light goes out. The alternator keeps charging until the 2 terminal senses system coming up. Most regulators are set at around 14 volts. The alternator is always charging to some degree.
 
It is clear that one circuit is keyed and that circuit is NOT the indicator light. So for a Delco equivalent circuit that would mean for this alternator that #1 and #2 are both keyed but not obviously so. And that does work too.

I could have worded it better true and I was lazy in not looking up my Delco diagram where I got on the wrong wire right away. End of the day he is likely to replace the bulb to find the parts guys were not lying. Thanks for the corrections, forums can not be beat for this aspect. Someone is always double checking what gets posted.
 
Good to know, assume your talking Motorola? Had one I R&R 3 times and elec shop assured me alt was OK. Didn't believe them till now.
 
Thanks for the info. I am waiting for the new pulley to show up so I can put the alternator back on. I will let you know if it charges with a working light.
 
Yes Motorola, deere does have a pigtail to install a delco on there and it looks good, Tim S. pointed this out awhile back was used on a 7520 4WD tractor. We had one on our late 1968 built 4020 that came with a Motorola for 35 years? Local dealer knew nothing about the pigtail, but had three of them on the shelf, and it was the go to guy that didn't know. The dealer I grew up by knew the number in his head, so I called him to tell the dealer that I was at to get one. Think they sold a few after that.
 

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