Diagnosing battery going dead

[Rembrant]

Hi Folks,
I just found out this week that the battery in my 1980 F150 project truck will go dead pretty quickly when parked and left unattended. I put my meter between the neg post and cable and it is showing a 3.5amp draw somewhere...which is huge? Anyway I pulled each fuse individually and nothing changed. Blower motor is disconnected as are the tail lights and transmission and transfer case etc. I finally unplugged the voltage regulator  and the 3.5amp draw disappeared.

Would the regulator cause this or would it be wiring?

I also just installed a new 1G alternator and when running My meter was showing 14.9v at the battery which seems a little on the high side but not too wild.

Ground cables are all brand new.

Any comments good or bad before I dig into it again?

[Gary Lewis]

That is a LOT of current draw.  I think you have a bad regulator.

As shown below, both the alternator and regulator are always connected to the battery, so either could do it.  But you disconnected the regulator and the current draw went away, so it must be the regulator.

[Rembrant]

Thanks Gary,

I have another voltage regulator I can swap in to try and see what happens. I'll do that tomorrow and report back.

[reamer]

Try using you volt meter in "AC" mode, with engine running, if there is an AC voltage reading at the battery posts, it could be a burnt diode in the Alternator.
This is how I found the alt was killing my battery in my Ford Escape...

[Rembrant]

Swapping out the voltage regulator seems to have cured the issue! I had a couple spares, but all I could find was the original Motorcraft one from my 1984, but it worked. Oh, and the voltage is better now when charging (@ 14.1v) instead of almost 15v previously. Back in business.