An LED illuminator includes a connecting member, a lamp cover, a hollow lamp cap, a plurality of LEDs received in the lamp cover, and a sealing member. The connecting member is a hollow cylinder. The lamp cover couples to and seals a first end of the connecting member. The lamp cap has a top end coupling to a second end of the connecting member opposite the first end and a bottom end defining an aperture. The sealing member defines an annular slot in an outer circumferential surface, with a diameter not smaller than that of the aperture. A portion of the bottom end of the lamp cap around the aperture engages into the slot of the sealing member. A channel extends through the sealing member with a diameter not larger than a conductive wire.