Problem starting my '89 Mustang

Something is stopping the start signal from getting to the starter relay(solenoid). Either a clutch safety switch if this is a manual transmission, or a neutral safety switch on automatic. Th clutch start switch is more than likely on the pedal assembly, and has red/light blue wiring going to both sides. You can disconnect and jump this switch connector with as little as a paper clip or equivalent. If it starts with key it needs a clutch start switch. On the automatic, the wires would be white/pink, and red/light blue. It looks like it is a multi terminal connector, I am not showing a location for it, but I would start with the trans shift linkage, and if not there the floor shifter. It should be closed in park/neutral, or you can jump the terminals the same way for test purposes. In either case if it still doesn't start, check for power when the switch is in start, at the white/pink wire(auto), or one or the other red/light blue(manual). If these do not light a test light, you may have a faulty ignition switch, or circuit betweenit and the clutch/neutral safety switches.