Alternator or regulator?

[Fordsandguns]

I have a drain on my battery unless I disconnect the negative cable. It started as a slow drain and now after about six hours the truck will not start. I have been checking the wiring but haven't found anything out of the ordinary.
I know the diode in an alt can fail and drain a battery in a hurry. Every one that I have had fail like that did it suddenly, no problems and then one morning it would be dead.
This is different so I wasn't sure.
I don't have the spare cash to go buy a new alternator so I'm hoping it is the regulator.
I have been reading the other threads about similar issues but I just wanted some input before i go changing parts.
I don't need to waste any money if I can prevent it.
Thanks in advance for any help and advice.

 

[Wicked97]

Same problem here. Pull the alternator and have it tested. I'll be doing the same thing in the morning.

 

[chris142]

Remove the wires at the alt. See if the battery still drains

 

[Fordsandguns]

Remove the wires at the alt. See if the battery still drains

You know, I should have thought of that. Wow now I feel dumb! I guess getting frustrated looking for the problem I overlooked the obvious way to find out. Thank you.

Can the testing machine tell if the diode is failed allowing it to drain the battery?

 

[Blind Driver2]

Can the testing machine tell if the diode is failed allowing it to drain the battery?

The good bench models can. I don't see how those new electronic hand held would do that.

 

[Fordsandguns]

The good bench models can. I don't see how those new electronic hand held would do that.

I'll take it off and have it put on the bench type. As far as checking the charging I have a multimeter and a battery/load/charging system checker. It is charging at 14.4-14.5 at idle with the accessories on. But it won't test the amps or the diode so I guess after Christmas I'll pull it and take it to be checked.

 

[79jasper]

The guy at o'reilly said their handheld will check the diodes. I had one that seemed like it was over charging because all my lights were all of a sudden brighter than ever. It tested fine though.

 

[Black dawg]

anything that will drain 2 batteries in 6 hours, will be warm. most likely the regulator.

 

[79jasper]

anything that will drain 2 batteries in 6 hours, will be warm. most likely the regulator.

Good point. Sometimes we overlook easy stuff like that.

 

[Tim4]

Disconnect both negative cables while you install the new regulator or else you could have the same issue all over again.

 

[Fordsandguns]

anything that will drain 2 batteries in 6 hours, will be warm. most likely the regulator.

I happen to have only one battery at the moment. But it's a G31 not the 65 like they came with.

 

[Fordsandguns]

Good point. Sometimes we overlook easy stuff like that.

That IS a good point!

 

[Fordsandguns]

Disconnect both negative cables while you install the new regulator or else you could have the same issue all over again.

Definitely. Don't need to fry the new one.

 

[Fordsandguns]

Okay, new alternator, new regulator and new battery.
Alternator finally bit the dust. Then the battery died. Then the regulator started over charging. So they all got replaced in less than a week. Worked fine for a few days, now while driving the volt meter drops real low for several seconds and then comes back up. It does this repeatedly. Checked it with a volt meter, at idle it is steady but raise the rpm's up to around 2000 and it drops to 13.0-13.2 range then back to 14.3 or there abouts. Back and forth.
Had it checked at the parts store and their machine said it is fine.
I have double checked all the connections and everything is fine. Have looked for a short and haven't found any yet.

HELP!

 

[79jasper]

Should be the glowplugs coming on to limit voltage. Hook a light up to the glowplugs output wire and see if it lights up when the voltage drops. It's setup to keep from over charging.