It appears the listed part for '92 was superseded by 5U2Z14300B. It carries a $160 list but can be had for $~80 online.

Nothing wrong with making your own, though - it's pretty straight forward. Follow the factory layout, use any heat shielding and brackets from the existing harness where needed.

You can also have custom cables made to match the lengths of the OE harness if you don't want to make it yourself. Remove the harness, measure length of each leg / wire and supply all the info (e.g. double ground leads off battery ground, double positive leads off battery positive, the length of each one, etc.) to the manufacturer.
Have ordered from this company before with good results:

Just add the solenoid 'S' /start wire yourself using high-heat rated 12-14awg wire with the appropriate terminals. Use plenty of dielectric or electrical grease on the starter solenoid terminal connection as it is exposed to harsh conditions.
-Panther info & FAQs-

Former owner of a Grand Marquis with a few mods, Grand Marquis "LSE S/C"