Snap On CT4C test light has a GE 189 bulb, I could not find one, I did use OEM tools # 25020 was on Amazon for $9.18 for 2.
ALSO: Snap On EECT307A0 test light has #6614F bulb, I did use OEM tools # 25888 (lights up red) was on Amazon for $6.59 for 2.
Bob