Chainsaw Repair

Ok first timer here, what a great place for chainsaw guys. I have a Rancher 50 I bought new in the mid to late eighties. This saw has been great and continues to run like a top.  The problem is shutting it down, the kill switch finally gave it up. I was pleasantly surprised to find one on Partstree ordered it and installed it only to find it didn't work. I feel like a real dummy, there is only one wire to plug in, am I missing something? Thanks for the help.
http://www.partstree.com/parts/?lc=husqvarna&mn=50+Rancher+%281983-01%29&dn=084200007

I went and looked in the workshop manual but didn't find anything about the switch

Looked at some parts list of saws of that era and seen the single wire on the switch. Looks like where the switch is mounted is metal and the switch shorts to the metal body to shut the chainsaw off?

Had this problem on a Stihl 042 and the area where the switch was mounted was actually isolated from the crankcase. There was a broken jumper wire that connected the handle  body to the crankcase ground.

The switch should ground thru side on the old version. Newer has a metal part going out under the tab you put the cable too.
This tab is meant to be fastened with a screw in case to ground if it has hole in the end. If not it is two tab's and you ground one.
If it is a white top you have there is no hole to put screw in to ground the newer type switch.