Charging problem

[Rocket350olds]

1986 olds cutlass supreme the battery reads 12.5 volts and when you disconnect the alternator to battery wire the alternator charges at 16volts then I hook it back up and it goes to 12.5 volts and pulls the engine down causing it to overheat. All the grounds clean and new positive and negative battery cables added a frame to block ground, replaced the fusible links on the starter post to the fuseblock. 4th alternator installed and 2nd battery

 

[olds307 and 403]

It causes your motor to overheat? It sounds like a short to ground.

 

[Rocket350olds]

Causes the engine to overheat because the alternator is working at max capacity but I'm not sure where the short could be

 

[Ribbedroof]

At the very least, the regulator in the alt is bad, it should not produce 16V at the terminal. Should be between about 13.8 and 14.2

 

[airboatgreg]

1986 olds cutlass supreme the battery reads 12.5 volts and when you disconnect the alternator to battery wire the alternator charges at 16volts then I hook it back up and it goes to 12.5 volts and pulls the engine down causing it to overheat. All the grounds clean and new positive and negative battery cables added a frame to block ground, replaced the fusible links on the starter post to the fuseblock. 4th alternator installed and 2nd battery

First thing is never disconnect the alternator output or a battery terminal while the engine is running.
Check the voltage{with a known good accurate voltmeter) at the alternator output(big wire at rear of alternator) while at 2000 RPM when you KNOW you have a fully charged battery with all accessories off. Then check the voltage at the battery using the SAME return(Ground) You should be within about .5 volt.
Let me know

 

[Rocket350olds]

Checked at the alternator voltage while using battery ground and it was 12.10volts and dropping while revving up voltage at battery was the same no accessories on and the alternator is charging cuz the magnet is energized and can smell belt slip when revving and the belt is tight

 

[Ribbedroof]

Are you saying that it was making 12.1 volts at the "BAT" terminal while system was connected and engine running? Could be a bad diode in the alt. 12.1 while running is not enough. Sometimes the battery lamp won't come on full bright while running with a bad diode. It took me driving at night to see the very dimly lit battery lamp last time i had a bad one....couldn't see it in the daytime.

 

[Rocket350olds]

It was 12.1 volts and discharging wont maintain voltage and it's the 4th alternator

 

[Ribbedroof]

Does your parts store load test them in the store?

Is the charging system wiring as-built by GM, or has it been dorked-with?

Unhooking an alt charge wire while running, as mentioned above, is a BIG no-no, as it can kill components or even spark a battery explosion, which is not something you ever want to be around.

 

[Rocket350olds]

Original alternator was load tested and nothing wrong with it and original wiring