Knowledge level: I've had this truck a month, never had a carburetred engine.

I have a 1979 f150 inline 6, it has the ALT light. ALT light doesn't work currently along with anything in the dash. I've traced this to the previous owner removing wires, the terminal that supplies power to the cab has no wire .

The alternator isn't charging the battery. 12.5 battery, while running drops to 12.2. Connected F terminal to positive for test, lights brighten.

Checked wiring at alternator for tight fit and battery, no corrosion.

Read some posts about the voltage regulator, so I got a new one. Noticed the I terminal had no wire to it.

Same voltage readings as before. Then found this thread: https://www.ford-trucks.com/forums/1079770-help-with-79-f100-alternator-not-charging.html

My understanding of this is that power to the I terminal starts the alternator? Me missing this wire is the cause of the non charging status. That missing I wire connects at the other end of the ALT light, and because it seems like I'm missing the wires that go to the cab and from the cab the alternator cant get started.

Find wires that go to cab and from cab.

Correct or no?

 

Do you have a DVOM (multi-meter)? Or Powerprobe?

Externally regulated alternators "don't know how much voltage to put out" or "when to turn on"

Thus the regulator comes in to play.

The I terminal is "normally" used for the Indicator. But not always used.

You can google Ford Voltage Regulator Wiring Diagram for alot of help. A good starting point is making sure your Alternator is good with a meter. At full field it will put out 19+ volts which will fry your battery but you will know if it charges anything.

 

 

I checked the voltage at the battery with my multimeter, would I check the voltage at the alternator at ground and at the Red terminal?

That "normally" used is what's throwing me, since the truck is so new to me, I'm not sure what the exceptions are or how to look fro them!

It seems from that diagram that I temrinal is whats going to the lamp. What does the 20A box on the other side mean?

This is the empty three prong terminal.

 

That three wire connector has direct correlation to charging! I got so frustrated with my pile of wiring I started all over with mine. Jerked out all the wires and re-did them!! I would redo yours if you are missing wires, just my opinion.

 

 

Blast. Is that a basic terminal I can buy someplace and wire up? I'm not quite sure how to search for it in a parts website.

I've seen some pictures of that side of the terminal. Any pics of where it goes from there? I just messaged s guy who is doing a 3 G for picture too.

 

PM Sent................

 

I would start with replacing your batt cables and be sure to run a good ground to engine and chassis.

 

Matt- Do you have power to your cab? You can check by seeing if headlights work.

 

I must have not hit "submit" before. Headlights work, the light for the display on the thermostat works. Gauges don't work, blower doesn't work.

 

Yeah someone really hacked your wiring up. You shouldn't have any cab power with that unplugged. Can you take a few more pics so I can 'look around' under your hood; just around the right inner fender. Specially of the solenoid and the battery. Maybe a good one zoomed out of the entire area.

 

 

I think your three prong connector has been bypassed. Can you confirm the yellow/white & green/red wires are intact and connected as illustrated in this picture?

 

I did a search and there is still one alternator wiring harness available should you decide you need it.

Harness, alternator to regulator
Fits: 79 F100-350 w/ ammeter and oil pressure warning lights and 40 or 65 amp alternator.
D9TZ-14305-C

NOS Parts Source, Olathe, KS shows 1 (913) 220-5746