You say a 40 amp ssr but what type one with dc+ dc- ch1 or just a regular 40 amp ssr? Where do I hook up my orange wire ch1 and will it be ok to run my + wire from starter even if motor is dc

This is the one I purchased can I use this ssr for my radio remote

This ssr is just a high amp isolated switch. It senses power either on or off on the DC voltage side and closes a switch on the already powered but open circuit of the AC voltage side.  Once the ssr's AC side switch is closed the AC circuit attached to this switch is completed and the device that is attached to this circuit powered and ready. 

The DC side can either be getting it's controlled power from a micro controller or a RC receiver getting it's signal from a RC controller. The AC side needs it's own AC power source. I guess it could be a powered DC source also. 

The big thing here is this unit you have here can handle up to 40 amps of load on the AC side. That's a lot. Also once the dc voltage is turned off the AC side switch will open. I don't think this is a latching relay where the AC side will stay open when power is lost. 

Here's a good video on using and wiring this ssr:

So as of now I have  a turnigy on/off switch, a 40 amp dc to dc solid state relay, I’m thinking I need a step down 24v to 12v because my starter needs 12v to activate but my sabertooth runs on 24v......... I  understand I run my + wire from starter through the ssr, but where do I hook up the 2 wires from pwm switch?

Will the Turnigy R/C Switch be big enough to handle your load? It's only rates for 13 volts and 10 amps. From what I read above you place the pwm switch between your receiver to the SS relay. Here's a couple videos:

Great find Dave!