1989 honda civic runs but when you turn lights on car stalls out. Have checked alternator, fuses.

CHECK ALTERNATOR DRIVE BELT TENSION.MAKE SURE IT NOT TOO LOOSE.AND CHECK YOUR IDLE SPEED.IT SHOULD BE 700 - 800 RPM.IF IDLE SPEED TOO LOW ALTERNATOR WONT TURN FAST ENOUGH.BUT CHECK ALTERNATOR OUT PUT AT BATTERY.IT SHOULD BE 13.5 TO 14.5 VOLTS.IF NOT PROBLEM IN ALTERNATOR.CHECK ALTERNATOR FUSE AND ITS BATTERY FEED WIRE AND VOLTAGE REGULATOR WIRES.

Hi! The battery may be weak and faulty resulting to not taking charge from the alternator thats why it stalls when lights are turned on. You will need to replace the battery to correct this. Hope this helps and have a good one!