I recently got a 2004 Freestar SEL, and the Trac light was a problem. This tread was helpful to point my mechanic in a starting direction. They tried a few things, and the problem disappeared for a week or two, then returned as a solid problem that would come on about 30 mph, and stay on until the engine was restarted.
Of course the cruise control would not activate when this light was on.
I took it back, with the light activated, and they checked for ABS codes and found that there was a C1288 code set.
When the mechanic checked their info database on alldatapro.com, he found a reference to a Technical Service Bulletin 07-14-10 "Traction Control Lamp - ABS Lamp - ABS Self Activation with DTC C1288" that covers 2004-2005 Freestar and Monterey.
It points at the ABS Module, the HCU and the Brake Pressure Switch. My guy opted to replace the Brake Pressure Switch as the lowest cost option (bless him!), and said he also saw where this is the primary part to replace. $99, and a little over an hour later, I cruised away with the cruise control back operational and the Trac light turned off.
I'll let you know if it returns.