I have two thermostats each with 2-wire for heat only.
I also bought a new spool of 18/2

My question is the color coding.

with the new spool it is Red and Wht
I assume red is hot and Wht is to heat.

If I were wiring to a new digital thermostat I assume I would use
Red to R and White to W.

My other thermostat wires are a little different

the oldest one is Blk and Wht
here can I assume Blk is hot and Wht is to heat?
so to wire it I would go Blk to R and Wht to W?

Then there is the other drop which is Red and Blk.
Here I would assume that Red is hot and Blk is to heat
so to wire it I would go Red to R and Blk to W?

Once in the zone controller box
for each zone I figure that the first TT sees the 24vac
and thus would be wired with the R drop
and the second goes to heat and thus out to the zone valve
and thus would be wired with the W?

My unit is short cycling all the time and I think there is a problem in the t-stat wiring - and I am also changing the T stat.

 

With a basic two wire system.... the color is unimportant. One wire to Rh and one to W.

 

Thanks PJ
does R going to the first TT matter. It looks like on one of my drops R is first TT but on other drop it is second TT.

 

You mention zone valves. What brand? Photos are helpful.

 

I am just using a pair of Taco 555s 3 wire heads.

 

You mentioned zone controller. I'm guessing it has multiple TT inputs ?
The polarity/color is unimportant there too.