My motorhome has a dash-mounted momentary switch which connects the deep cycle battery in the back to the start battery, in case you need a boost. I never found it to work that well since the rear battery always seemed to be too discharged when I needed the help. There is another switch which allows you to run the dash mounted radio from either of the two power sources. My rig is on an Econoline chassis which is notorious for the instrument cluster voltage regulator failing & draining the battery. My solution, cheaper than fixing the regulator, was to buy a gizmo that automatically cuts off the battery if the engine-off current draw exceeds a certain ma. Works really well; has a little key fob remote and sorta acts like a security device.
During the late 70s oil crisis my Dad & my uncle bought great big woodstoves and started cutting wood like madmen. Dad was hauling it with a Ford Courier-somewhere I have a photo, he must have had an honest ton on that poor thing! Anyway, they went to some farm auction and bought about a '49 Ford F-4 or F-5 stake body truck with the intention of using it as a hauler. The big day came to try and get it running. I remember I was given the option of riding in the Ford or in whatever pickup truck they were pulling it with; Dad told me the Ford "might blow up" which scared me out of hopping in. Wished I'd chanced it, now! I remember they drove at least a 1/2 mile but it never fired. Next thing I know the truck was gone. So much for that idea!
Oh...there was a small downhill stretch just before you got to our house. (as "hilly" as it gets here on the coastal plain) The Courier was a 5 speed. Every single time-EVERY. SINGLE. TIME-that Dad came to that hill he would cut the ignition, let it coast a bit, then flip it back to "on" and the engine would backfire, POW! POW! POW! I tell you, I don't know why that truck was completely worn out at 50k, guess those Japanese just don't know nothin' 'bout buildin' pick-em-up trucks
