I own a 79 f100, 351m c6. In the last 24 hours the battery has totally discharged 3 times. After the 1st two times I changed batteries to a new one from my f250, same problem, after about 4 hours it is so dead it doesn't even illuminate the oil light when the key is turned on. Nothing obvious left on, brake light etc not activating (had that happen once before). Where do I begin checking the system for this power sapping ghost.
Thanks in advance

 

That happened to me once. Went outside after dark and noticed that the light under the hood was staying on.

 

Connect a 12 volt test lamp between the negative batery cable & batery post and pull fuses until the light goes out. Make sure everything is turned off including the dome light.

 

Has to be a prety good draw on it to drain the battery that fast. The above way is the easiest thing to test with. I have used that method many times.

 

It appears to have been the regulator. Replaced it 3 days ago, no troubles since.
Thanks guys,as always for the responces