Left brake and left turn signal not working on tow vehicle

If I read your post correctly, the toad is a non issue. I assume you've used a test light on your motorhome plug and found the left turn wire is dead. This should be the YELLOW wire. First thing would be to ensure this wire is good. I.E. not disconnected inside the receptacle. Trace the wire backwards as far as you can looking for a frayed or broken connection. Worst case is you'll have to run a new wire.....Dennis