Jump +12V to the “start” terminal on the starter. (Um, make sure the car is in neutral, yeah?) Should it be locked?
There may be a safety interlock relay and there is a brake relay connected to a switch in the clutch or AT.
The relay(s) are, I think, in the fuse box under the hood.
Here is the Wiring Diagram section from a ’99 service manual. It should have everything you need. (Page 120.) ’98 was a change year, so if this doesn’t seem right, let me know and I’ll send the ’97 document; I don’t have the 98 document.
edit: You said MT. The brake switch is on the pedal cage next to the clutch. IIRC It opens when the clutch pedal is depressed. It could be a bad switch, it could need adjustment, it could be the relay, but my money is on the safety system.
In ’97, disconnect the battery. Switch on the ignition, turn it to “run”. Reconnect the battery. This will reset the security system. Or not . . . try Google.
