Brake and blinkers not working 70 dart

The cancel cam is more or less the upper half of the switch. A lot of owners/service techs would replace only that. I always recommend replace the entire switch assembly. Even though it is a sitting in the drivers seat service, I don't want to do it again any time soon, my vehicle or customer pay.
A lot of the aftermarket switch assemblies and cams ( ebay offerings ) have proven to be junk. Those buyers bend and tweak on the tiny contact parts to make the electrical work only to have the mechanical hold on and cancel function fail a short time later.
Our member SlantSixDan can direct you toward a OEM quality switch.