by a cam lock 16 movable between stops 16s the barrel has lateral holes 1h along its length as mentioned above for insertion of guide pins during molding to insure barrel straightness and smooth operation in using the above apparatus for testing wire continuity in a live circuit plug 14p is inserted into outlet 13b and clamp 14 is clamped to ground the wire to be tested is hooked by body end 14e then the operator pulls trigger 17 to drive pierce probe forward so that its pointed end penetrates the wire insulation to provide a new branch of the wire 39 s circuit via probe 5 strap 3 bulb 6b wire 6w and wire 14 lighting bulb 6 if the wire being tested has any breaks a terminal may be tested by sliding end extension 2 forward so that its spring detent 20 falls into hole 14a to contact probe 5 and complete a similar branch circuit to light bulb 6b if the terminal is live a wire per se or a wire in a powerless system is tested by inserting plug 14p in outlet 13a and otherwise using the testing procedure for powered systems a pre check of battery 10 and bulb 9 before powerless system testing may be made by touching clamp 14 to the extended end of probe 5 fig2 shows such parts assembled for functioning in accordance with the foregoing discussion it is evident that those skilled in the art once given the benefit of the foregoing disclosure may now make numerous other uses and modifications of and departures from the specific embodiments described herein without departing from the inventive concepts consequently the invention is to be construed as embracing.