I have a 1989 F350 diesel, with a voltmeter as opposed to ammeter or indicator light. Alternator is not putting out. Alt is new and tests good. Regulator is new heavy duty Napa unit.
I can't find the correct diagram for the volt meter application. All fuseable links are good and all wires checked good with ohm meter. Any body run across this? A good schematic would sure help.

 

My understanding is regardless if you have a voltmeter there is still a Charge/Battery indicator in the instrument cluster..perhaps I am wrong. I am certain Ford uses the same Light Green/Red wire to turn the alternator "On". There should be power on this wire when the key is in the Run position. if it is missing, there is your culprit.

This basic diagram may help.

 

Is the plug on the alternator in good shape?

 

Both the Alt and Regulator plugs are new. The green/red wire is in the I (indicator) position of the regulator. This is what the Ford diagrams show.

 

Is there power on the Light Green/red wire with the key in the On position? If not, there is your root cause. You need to chase that back into the cab, instrument cluster, ignition switch.

 

Yes, there is power at the Red/Green wire with the key turned on.

 

Is there battery power on the Yellow wire as noted above? The Light Green/Red wire controls turning on the alternator. It also needs power to create the field, that's where the yellow wire comes into play. Unlike a generator, an alternator needs power to start the charging process.

 

Thanks to all who replied. I learned the hard way that you cannot use an LED bulb in the ALT light circuit. I had some thru voltage but not enough to excite the relay. I replaced it with an incandescent bulb and now have normal voltage at the green/red wire and an operating alternator.

 

Yes, you were correct about the LED light. If you had posted that you had swapped it in, we would have pointed you to the easiest fix.

Thanks for posting your success and hope to see you soon!

 

Glad you got it fixed and replied back.