The Boss Tera Echo Latching mod enables you to have an external latching foot switch that you can press to enable the hold function on the Boss Tera Echo and you dont have to hold  the foot pedal on the Boss Pedal, you can simply press it once and leave it in hold mode and press it agian to turn off the hold mode. 
 
The Mod can be done to install just the external jack for the hold function. 
And I also sell a latching hold function foot switch that works with the hold mod. 
 
The External Latching Foot Switch uses a standard TS patch cable for operation. 
 
This Mod is to send in your fully functioning Boss Tera Echo pedal for me to install the extra jack for the hold mod. 
 
The turn around time for the mod is 1-2 days.