I have my meziere electric water pump installed and all wired up except for the key on source to actuate the relay. does anybody have any experience with these, where's the easiest/best source to tap into for the 30 amp relay
I would be tempted to do this with a separate relay directly from the battery. However, you failed to mention the model year of your Mustang. So I can't directly recommed where to tie the pilot duty coil to.
If the 99-04 MY, consider using F2.34. There are tons of other places to tap for a low current pilot duty application. The CCRM is an easy spot. It really depends on what's easiest to get at and your preference.
If you would like a copy of the wiring diagrams, I may be able to help. PM if interested.