Dash warning light

From my experience...
A non PATS coded key SHOULD not turn the STARTER...!

If ANTI-THEFT were invoked... you can attain a not start condition which the Owners Manual says must be cleared by the dealer.

A working PATS key should disable the anti theft... by turning the ignition on... ELSE try your other key.

The SecuriLock [PATS]
passive anti-theft system is not compatible with
non-Ford aftermarket remote start systems. Use of these systems may
result in vehicle starting problems and a loss of security protection.

Owners Guide (post-2002-fmt)
USA English (fus)

OWNERS MANUAL
Ford 2003 Mustang Owner Manual

SHOP MANUAL
Ford 2003 Mustang Workshop Manual

You should be able to find all Ford Makes & Models Manuals at this website:
https://owner.ford.com/tools/account/how-tos/owner-manuals.html

It is also here:
http://justgivemethedamnmanual.com/ford/2001-ford-mustang-owners-manual

there a section in the owners manual that speaks to warning lights, what causes them and what to do about there after.

Most likely reason is that the tail light fuse blew out. The dash lights have a seperate fuse, but it is wired in series with the tail lights, so that if the tail light fuse blows, the instrument cluster lights also go out. The dash lights going out is sort of a warning to let you know to check your tail lights

If you did not get an owners manual with your truck ( purchased used ), you can download one from Ford :
https://www.fleet.ford.com/maintenance/owners_manuals/default.asp

The aux relay panel is not documented for some reason

The picture below is the only one I could find that may be what you are looking at. It's on the bottom below the speedo and RPM gauge. Didn't say the color so I wasn't sure. I hope this is what you're looking at. This should be in your owners manual if you have one. If you don't have an owners manual and you would like a copy, you can email me at [email protected] with your make model and year and i will be happy to email you a copy. Hope this helped and good luck.

ITs a fuse or probaly a reallay or u have a loose wireing under the dash

That is your low tire pressure warning. One of the tires is low, a TPM may have failed, or the system needs to be reset.

sound like a lose wire.take dash back out and check the wires that goes to dash.wires could have move out of place when you removed the dash.

That sounds like your traction light. Does it have a trac button on the dash? If so, try switching it and see if it helps.