hi guys, should a 79' f-150 run without the battery? I thought I used to be able to disconnect the cables from batt. and engine would stay running, now it dies instantly. I have had alot of charging probs with this truck last winter. I had a short that would kill the battery when the truck was off, I think that ended up being alt. it tested bad so I bought a new one, so I now have a new alt, voltage reg, and starter solinoid, the short is now gone, but the truck is still not charging properly take cables off truck dies, and it acts like it want to die on the road when the batt gets low, tach goes crazy, but then some of the time it seems fine I'll get home test the batt. with ohm meter 11 to 12 volts out of batt after running the headlights for 10 min. then sometimes out of the blue it will quit charging. Oh yeah new starter too, anyone run into this or know how to test? should a prong on alt be pushing out 12v at all times?????? It really dosnt matter I am just wanting to know because I have been fighting this prob for a while, the only thing that is left that is not new is the wiring harness and the little capacitor beside the voltage reg. Starting next week this truck is getting a makeover anyway it is getting 460 that I painted last week looks pretty good maybe I post pics later, the engine received a gear drive, a mild cam, a Elderbrock rpm intake, and a Holley 750cfm double pumper if it dosnt smoke to bad. The truck is also getting Dana 60 axles all around " converting to F-250 leafs" the only thing that looks a little complicating is going to be the steering system 2 different systems. The truck is also getting a nice flat bed from my donor truck, "the frame was no good"

 

Running an engine without a battery connected to the system will blow all sorts of things in the alternator.

If has been done.. off to buy a new one or rebuild it.

Dis-connecting a battery with the engine running to check charging is a throw back to the days of GENERATORS which were done away with in 1965

It was an old mechanics trick to EXCITE the generator to get it to start charging.They were of DC current

Alternators are of AC current and cannot be abused the same way.

Ignition systems require a minimum of 5.8 volts...if they don't receive that the engine stalls.

You have an Energy problem

Don't be surprised if you have pooched another alternator

 

Dont think I ruined another alt, it is still charging half the time, but ya sure cant count on it. I do toltally understand what you are saying though I have heard it before, but if I remember correctlly years ago I did switch a batt, with the engine running, several times and no prob, I couldnt even begin to do it now engine dies right away. truck still fell on its face with all brand new components including 2 new different alts new voltage reg new solinoid and new starter no go, no charge, oh well switching to the 460 components anyway I know it will charge then.

 

Two things control the charging system

Alternator (Internals) & Voltage regulator.