RE: Replace royal titan servo?
Your Hitec Rx will accept Hitec S, JR, Airtronics Z and Futaba J (in the case of the J some versions do not even require the removal of the tab) plugs. All these current plugs are of the same polarity.
Your drawing looks like the old style Airtronics plug that along with a number of others is obsolete. This plug in the case of airtronics has the positive and negative lead reversed from all the modern plugs and to be used must be reversed agine with a new style plug installed. Now in the case of Old Royal stuff I,ve no idea what they used but from what you have its most likely as per 'old Airtronics'. Look at the servos lead carefully is there a very narrow white or gray stripe on one of the leads?
John