Welcome to Pinside. There's a schematic and manual for your game on IPDB.org.
If you press the Credit Button (in the red box) the Credit relay should fire.
Aladdins Castle Credit relay (resized).jpg
If it doesn't, carefully check all the switches and fuse in the path shown in red.
BTW, unless you've been at this for a while cleaning all the (contacts, plugs, relays, etc.) is just as likely to introduce problems as resolve them.
/Mark