1990 Honda Civic SI Power Problems
 

Hi there! I have a 1990 Honda civic si that when I have the battery on the charger it starts up and runs fine, but when I take off the charger the car runs for a few minutes and then dies, The alternator has the wire ran to the fuse box area and the wires coming out of it are getting power, could it be a bad connection to the battery or to the fuse box area? I have tried running a wire directly from the alternator to the battery and that did not fix the issue. Only thing done to the car is aftermarket shift lever, exhaust, and cold air intake. TIA :)

Sounds like weak battery and alternator is not charging
Back in the day, use to start the engine and then disconnect the battery
If the engine continues to run then the alternator is working properly
If not then alternator is not charging.

Would take volt meter and measure battery voltage. 12.5 volts is normal.
Less is weak battery (charge up and see if it holds charge)
The start the engine and check voltage again. Should be13.5 to 14.5 volts.
If not then troubleshoot the charging system is necessary.