I'm not familiar with your vehicle, but this Aerostar forum is a bit quiet so it might be a while before another owner comes along. To confirm that it is that relay which is clicking, you should be able to feel the clicking if you touch the relay's plastic case. Can you see the colours of the wires which connect to the relay? If so then there's a chance you'll be able to identify it on the wiring diagrams in the repair info section at
www.autozone.com - they just changed the site a couple of weeks ago and I think you have to register now to access that section, but registering is quick and easy (and free).
Relays will often click due to low voltage, so do you have a flat battery? Will the van crank and start? If it does then can you identify a circuit which isn't operating correctly? Interior relays would typically control circuits such as: fuel pump, power to PCM and ignition components, heater blower motor, rear window defroster, some of the lighting circuits, horn, power windows if fitted, fog lamps if fitted, etc.
If you're not used to reading wiring diagrams or if you have problems navigating the autozone site then let me know the relay's wire colours if you can see them, and I'll take a look at the diagrams.