Even with the high-output alternator, it wouldn't hurt to add a second battery, if you have room for it. Many years ago that's what we did with our 1965 Olds VistaCruiser ambulance. It came with a 100-amp alternator. For emergency equipment we had a roof-mounted Q flanked by four DoRay lollipop lights (two on each side of the Q), a Federal 174 beacon back over the VistaCruiser "hump", red and blue spotlights and red and blue grille lights. We took it to the local Sears and told them that we wanted two of their best Die-Hard batteries and wanted it hooked up so that if we turned on all that stuff, including the headlights on bright and then "romped" on the Q, we didn't want any of the lights dimming down. They used two big Die-Hard truck batteries on the wagon. We had used the kind of solenoid described above. The solenoid was a grounding-type. It had a single terminal on top that went to the foot button and from the foot button to ground. So what we did was to run the large 4 ga. cable from the solenoid to the number two battery, as well as the wiring for the lights. Then they ran the "hot" cable from Battery 2 to the hot side of Battery 1. Worked just fine. We could light that wagon up and run the Q, along with the Federal Interceptor with grille mounted speaker, and none of the lights would dim. Worked like a charm.
As to the Ford solenoid you suggested: they will work, but they're not the grounded type. On it there are two terminals on top. The left terminal goes to your foot button and from the button to hot. The right terminal you can use a small wire to go from it to the large right terminal on the side that will go with the large 4 ga. cable that goes to the battery. Your Q cable will go to the left side of the solenoid, regardless of which solenoid you use. By the way: you do have a brake on that thing, don't you? You didn't mention it.
