Battery going dead on 1978 f150
 

Guys my battery has been going dead when the truck sets for a few days. i have replaced the battery recently with the same result. If I take the positive wire off it sparks on the terminal even when the key is not on. To get by this i have been recently taking the positive off while it is setting. I am being told its prob a ground issue? I pulled all the fuses under the dash and it still sparks when touching the post. If it means anything to any of you the gas gauge quit working approx a month prior. Thanks!

Welcome to the site..

When you leave it cabled up, (with the engine cool) does the alternator feel warm even though it hasn't run?

Generally when the gauge quits working, it the fuel sender float has cracked (hollow brass) and the float sinks to the bottom of the tank. If you ground the fuel sender wire and the gauge pegs to full, the float is the cause...

I went through the same issue for months. Seems to have been a bad positive battery cable. Or like Hayapower suggested, could be bad alternator diode.

Ok apparently I am a terrible mechanic even though I already knew that. What i thought was the voltage regulator was actually the solenoid oops. So yes when the cables are connected the altenator gets warm. My dad said to un hook the cable and see if truck dies and when i did that it arc'd alot lol and fried my radio another oops. Also the battery is spitting out acid out the little drain holes which is what iu noticed on old battery (reason i replaced). So now i am thinking I should actually replace the voltage regulator first? Thanks and yes I am a newbi on working on vehicles ha

Sounds like either the voltage regulator or alternator or both are overcharging. I would pull the alternator and take it to a parts store for the free check.

Something to consider.
Invest in a cheap multimeter. If you connect the red lead to the battery positive post and the black lead to the battery negative post , at rest the battery should read in the area of 12.4 volts if fully charged and the engine off. With the engine running and all accessories turned off the voltmeter should read in the area of 14. 2 volts. With those conditions any readings other than what are listed are cause for further investigation.
Many vehicles already come with a voltmeter as one of the dash gauges and some are color coded to indicate normal areas. It can save a lot of time and work when checking the health of the battery and charging systems.

Thanks guys I changed the altenator and voltage reg and the problems went away. My fuel gage works again too lol