I have 40+ years designing wireless systems for some of the most demanding environments possible.
Although the wording of the OP's post is somewhat vague, if I understand correctly the OP is trying to use a wireless system to control the parking and brake lights on the towed vehicle from a wireless control located in the motorhome.
I strongly advise against using any wireless system for this purpose. All wireless control systems are inherently not 100% dependable. It is very unwise to use a wireless system to control a safety feature (tail and brake lights), as many very unexpected things can go wrong with the system.
- Design deficiencies
- Installation issues
- Communication reliability issues (interference, etc.)
- Environmental and Age Related Issues (consumer grade wireless systems become increasingly unreliable with with factors such as rain, humidity, extremes in cold or hot temperatures, wireless/hardwired connections to the vehicles, etc.
I recommend abandoning this approach if in fact it is designed to control safety features such as on the road use of tail/brake lights, etc.
If the OP needs help with a wired system, there are many here who would be happy to lend an ear and offer experienced advice to help get over any design/installation/operational hurdles.
Safety first (or was it profits? I can never remember which.)
Would you rather have a mansion full of money or a trailer full of love?