Not sure about your 98 - - however on a 2001 the dealer added keyless entry
module is located under the centre console.  You should be able to reach it
from the drivers side by reaching in and reward from the front near the gas
pedal.  On our vehicle the module is loose and connected to a wiring harness
that contains a small pushbutton switch.  Not sure what the switch is for,
perhaps something to do with the remote.