I picked up a used #4 Black Diamond pre-thumb loop camalot off the Mountain Project used gear forum. The price was right but the trigger wires had seen better days. I did not actually notice this in the seller's photo nor did the seller mention it when I bought. Although not a big deal I was a little annoyed when it arrived.
On MEC's website the replacement wires for Black Diamond C4 cams are $7.50 for two. Since I had an older model I measured the current wires to make sure I got a set that would work; about 21 cm for the #4. In the end this did not matter as the Ottawa store had all sorts of trigger wires dating back the original duel stem model. We managed to find a trigger wire for my original #4 marked at $6. The pre-C4 wires were actually on clearance so the final cost was $4.50. Not bad at all.
The kit comes with installation instructions for the various types of cams and trigger bars. Step 1 is to cut the tigger wire above the swage and step 2 is to remove the wire from the bar's cleat. The cutters shown had a hard time cutting the solid wire. It was in fact easier to uncleat and then cut.
Step 3 calls for the trigger wire to be straightened and removed from the cam lobes. As you can see in the following pic that the wire itself was rather brittle and came out in pieces.
Installation is straight forward. The only thing to account for, is that both trigger wires terminate on the outside of the cam for an older style #4 (also #3.5); other sizes face in and out. Note that the trigger wires should not be crimped tight to allow smooth motion of the lobes. After an initial bend with needle nose pliers, a pair of vice-grips, set to the desired width, makes the final bend easy.