Car instantly drains Battery

[Amiller2022]

I have a 1984 Fiero SE and I’ve replaced alternator, starter, battery, battery cables, and icm. It still acts as there is no power when I first hook the battery up the lights and everything will turn on but when I go to turn the key everything shuts off and then the battery dies and I have to go charge it. This has caused many batteries to no longer be able to charge.

 

[melsg5]

For a battery to instantly go dead a wire would have to melt from the amperage draw.
Are you testing the battery with a voltmeter before you hook up the cable and again after the start attempt?
Have you tested the ignition switch?

 

[92 Sunbird LE]

Large 12 volt short somewhere ....hooking up the battery cables to the battery should not spark if everything is off..new starter and alternator should be tested on a machine even if brand new. Alternator and starter large wires also...


Doug in P.R.

 

[omologato]

It amazes me how overlooked an ammeter is in diagnostics.

Remove negative cable from batter and place ammeter in series. With key removed from the car and no interior lights on or anything there shouldn't be more than 30mA of current.

I agree with Melsg5 in that for a lead acid car battery to go "instantly dead" that fast would require a HUGE amount of current, we are talking hundreds of amps of current. This would cause even the large gauge wires to become hot. And Doug makes a great point in that if there was this amount of current present you would get a rather large arc/spark when connecting the last battery cable to complete the circuit.

Most likely problem sounds like ignition switch or bad connection. Many grounds are non-insulated braided cables and end up rotting and fail.