The LaserWriter IIg I/O board is notorious for getting bad capacitors, so you are not alone. The IIg did not exist in 1989 - I think it came out in 1993 or 1994. As such, your printer is most likely a IInt or similar vintage that has been upgraded to a IIg (it's just a straight I/O board swap).
Are both lights on all the time, or do they start blinking a little while after startup? Both blinking = fuser heater failure (but more often with really old printers, it's a false alarm generated by dried out electrolytic capacitors on the AC power supply board).
To see if the problem is the I/O board, or something else in the printer, try this: Remove the little plastic flap at the bottom of the back panel on the printer (i.e. the side opposite the status LEDs). Behind the flap, there should be a hole in the metal plate and small black push button behind the hole. Turn the printer on, wait a while for the fuser to get up to temperature and push the button. The printer mechanism should generate a primitive test page - it just has vertical stripes. If this works, then the basic printer is ok and the problem is more likely to be the I/O board, rather than the electronics or mechanical bits in the printer itself.
Are both lights on all the time, or do they start blinking a little while after startup? Both blinking = fuser heater failure (but more often with really old printers, it's a false alarm generated by dried out electrolytic capacitors on the AC power supply board).
To see if the problem is the I/O board, or something else in the printer, try this: Remove the little plastic flap at the bottom of the back panel on the printer (i.e. the side opposite the status LEDs). Behind the flap, there should be a hole in the metal plate and small black push button behind the hole. Turn the printer on, wait a while for the fuser to get up to temperature and push the button. The printer mechanism should generate a primitive test page - it just has vertical stripes. If this works, then the basic printer is ok and the problem is more likely to be the I/O board, rather than the electronics or mechanical bits in the printer itself.