The ULT-4 (pictured on the bottom in the photo below) is fully compatible with the Fender® G-DEC® 3 series amps. The MS-4 (pictured on the top in the photo below) is fully compatible with the Fender® Mustang™ III-V amps as well as the Mustang Floor. The MS-4 is also fully compatible with the Fender G-DEC 3 amps with the exception of the printed text on the top panel of the MS-4 differing from that on the ULT-4. This can easily be updated with a labeler such as a "P-Touch" or similar product.
The ULT-4 is compatible with the Fender Mustang III-V and Mustang Floor products except when used in conjunction with the EXP-1 pedal. Therefore, we do not recommend using the ULT-4 with a Mustang III-V or Floor product and an EXP-1. Other Fender products that are compatible with the MS-4 and ULT-4 foot switches are listed below.
● Fender G-DEC 30
● Fender B-DEC