F-150 2001, 4.6 liter V-8, Battery kept going dead after a couple days parked, Paid automotive electric repair guy $900. after two trips he thought he had it but no, I put an RV type knife switch on the battery to keep it from draining down overnight.
Traced it to 20 amp fuse to the alternator field coil draws 3 amps with engine off
found that pulling the quick connect off the alternator killed the drain,
Now I am thinking maybe the ignition switch is not cutting off the alternator field coil circuit when turned off. Any thoughts?

 

Please tell us what the "Repair guy" replaced for $900.00 . I can't guarantee we will find the problem, but we'll give it a shot and the most it might cost you is some time and checking. What kind of electrical test equip do you have to work with?


Is the PCM power relay staying "Stuck on" ?

 

the auto electric guy said he found a shorted wire to cab, wasn't specific. next day battery dead. took it back. he kept it 4 days, called and said no problems. went home,battery dead next morning.
alternator field fuse pulled will stop the current flow as well aspulling the alternator quickconnect on field. pulling relays in underhood elect. box has no effect. not sure how to check PCM relays assuming I can find it. I have Fluke volt-ohm meter. thanks for reply.

 

PCM power relay is located in smart junction box.
Should be no power to alt with key off.
Have some doubts regarding some of the answers you received.Without a diagram one option is check the color wire with the power at alt and back track it to see where it comes from. A bit of work , but will be worth the trouble when you fix it for a lot less than , well you get my drift !!
Can you try this, remove the hot wire from the alt output terminal that goes to the battery. Now see if the drain is still present. If not Alt may have a problem.

 

Alternator is original?

With the connector disconnected, engine off, is there a voltage input on the LG/RD from the cluster.

 

alternator was the second thing i replaced after a new battery when the old one wouldn't recharge. pretty sure it's not the alternator since the field coil wire shouldn't have power to it with ignition off. just remembered I think I have a repair manual for it somewhere. maybe i can follow the wiring diagram. thanks.

 

hanky - the power cable from alternator to battery Plus for charging was one of the first things i checked thinking maybe a short in alternator wiring or diodes . that had no effect but replaced alternator anyway before taking
it to the "professional"!! let me find my manual and do some edu-ma-cating. it may have a wiring diagram to help me. thanks. forgot i had one until i wondered how to get a wiring diagram. i will update this thread if i figure it.

 

The IC supplies voltage to turn the regulator On, allowing current to flow from battery sense to the alt field coil. If the LG/RD (IC) is hot with key off, the field would energize. I wouldn’t think the IC circuit would be active key off, but something I’d check. Harness/connector issues etc. More so since the alt has been replaced.

 

what is LG/RD and IC? sorry to be so ignorant of auto terms. i was a radar repairman in usmc, instrument mechanic in gas company and supervisor 20 years- elecrical, electronic, hydraulic, high pressure gas up to 2000 psi, oil and gas. last 25 yrs on a computer array controlling high pressure gas lines in So. Cal. always worked on my own cars but nothing major.

 

You probably have more electronic background the the "Specialist " you took it to.
Regulator in your alt is internal within alt.
With the alt unplugged, is there power in the wire and/ or the terminal that wire connects to? One of them will lead us to the problem.