You will need :
Marker (Or something that you wrap wire around)
Step 1: Wrapping Wire
Start to wrapping wire around marker and secure it with tape
Step 2: Covering
Cover the taped sides aluminum foil, reflective side out.This will reflect heat from the heat gun away
Step 3: Heating the Wire
Heat the wire with heat gun,but when plastic come smoking let it stay minute or two and heat it again.
Step 4: Testing
Remove foil and tape.
Test the wire before you use it