Hi I'm Greg, new here.
77 F150 351m auto 2wd styleside green once upon a time.
I bought the truck last weekend for $500.
Battery goes dead. Has new battery. 14.8 volts to the battery when running.
If I disconnect the black/red wire from the starter solenoid the draw goes away. The voltage regulator is new. The alternator seems to be working. The engine is great, starts and runs super. Every thing seems to work ok, lights, turn signals, brake lights, heater. Only weirdness is running lights on front were very dim even when truck shut off but new light switch seemed to fix that. Now the running light on the psgr side does not work and the running light on the drvr side is intermittent. Tried pulling all fuses and checking, still the draw.
Rusted truck body. Had been sitting for a year before sold to me.
Not sure how many miles are on it. The odometer reads 09,710 so at least 109k?
I have a basic schematic that shows the black/red wire with fusible link going to the regulator and the alternator. It got too cold out to troubleshoot much further than pulling each fuse, narrowing draw down to black/red fusible link wire and replacing the voltage regulator with known good.
First post to this forum so bear with me a bit. I love the truck. Parts are so cheap and available. Lots of room to work and the layout makes sense.
Thanks,
Greg

 

Definately ether the VR or alternator. Removing both and having them tested at the parts store will verify one or the other. I suspect a bad diode in the alternator.

Josh

 

Welcome to FTE. Sorry I can't help you. I would think that the running light socket would be bad or the ground. Not sure about the charging problem.

 

Thanks for the fast replies! Tomorrow is supposed to be 51 so warm enough to take the alternator out and have it tested. I wanted to make sure it wasn't something further down the line. But pulling the fuses should have found that, don't you think? It could be a ground somewhere, it's very rusty. I hope it's in good enough shape to restore and drive for a while. An older guy gave it to his son in law who sold it to me. It's got white walls and original hub caps and a really nice tool box topper.

 

I would say you have it narrowed down.

Other than that you could run a test light or DMM between the negative cable and negative lug on the battery and start pulling fuses and disconnecting terminals at the solenoid.

A bad diode in the alternator can pull down the battery no problem.

Josh

 

The last electrical problem i had was with a engine ground wire. Wish i had found it earlier $400 and two weekends later and some fancy new engine gaskets everything worked fine.

Follow the ground lines and feel the actual wire. somewhere along the line I had managed to crack the actual wire. My guess got cold hit a bump snappidy doo da dey and instant troubles. If the wires feel fine look at the connection points.

 

Wiring continuity can only be verified with a multimeter. You can't "see" resistance and you can't judge the integrity of an electrical connection visually. A connection can look bad visually, but ohm out just fine. Conversely, a connection can look fine, but have very high resistance.

You can't use your ears to smell, and your eyes to taste. Use the right tool for the job; same goes for electrical.

 

I've seen a bad solenoid do what you describe too. Sometimes one can short out inside and ground out through the inner fenderwell, and still work just fine.

 

your alternator has a bad diode thats causing the battery to go dead !

 

True but you can see corrosion or maybe a missing connection and we can feel breaks.

 

Irregardless it's still a bad alternator...

Josh