Stem shifter cable options?

[WillWork4Parts]

Are the older Schwinn 5 and 10 speed bikes with stem/headset mounted shifters friction shifters if they’re not branded positron?

Yes...I would search for "Positron shifter" on ebay and take note of what NOT to buy...unless you are looking to actually match original equipment. Only 2 stem mounted Schwinn branded friction shifters come to mind and they are quite similar to each other, they are chrome plated with an S insignia, unlike the aluminum or black plastic Positron levers.

Indexed shifters and derailleurs took off not long after Positron systems made themselves popular.

 

[LifeBehindBars]

Those older ones are indeed friction shifters, as the wing nut on each maintains pressure on a fiber inner washer that holds the lever in its current position. You pull the cable lever downward against the force of the return spring in the derailleur to downshift (rear) or upshift (front), and then lift the lever for the opposite direction, at which time the return spring in the derailleur shifts the chain appropriately and takes up the slack in the cable. The Positron system (as noted) is entirely push-pull using a solid wire, sort of like a Bowden cable setup you'd find on the HVAC controls of a vintage car.

I'm not sure what you have to start with here... are you building off of a bare frame, or are you trying to match shift levers to existing derailleur hardware?

I have one bare frame and one complete bike. The complete bike is a 84. It has a thumb shifter currently which a couple of people have told me is correct but most people say was changed from a headset mounted one

 

[WillWork4Parts]

I have one bare frame and one complete bike. The complete bike is a 84. It has a thumb shifter currently which a couple of people have told me is correct but most people say was changed from a headset mounted one

Well, post pictures, including clear shots of the serial numbers, and we can help clarify with certainty.

 

[acg_schwinn]

The complete bike is a 84. It has a thumb shifter currently which a couple of people have told me is correct but most people say was changed from a headset mounted one

I couldn't find a Cruiser 5 catalog listing in the Findley collection prior to 1986, but the 1986 model is stated as using thumbshifters, for what that's worth.

Ref: https://fleetvelo.com/SchwinnCat/flschwinn_1981_1990/1986_crsr_03.html