If you want to use a 6v system, any 6v auto/truck battery that will fit into the battery box will work. I prefer an Optima 6v red-top battery.
Most 6v volt vehicles that have been used over the years have most likely had their battery cables replaced with 12v battery cables - these are not sufficient for use in a 6v starting system. A welding-supply store, large-truck repair service, or a farm-supply store (like TSC) should have 1/0 or 2/0 battery cables (or, they can make them)- a necessity for a 6v system to work properly. Make sure all connections are clean and solid (I also use a conductive, ant-oxidant, copper grease that is readily available in small jars at NAPA).
If you have a battery in your truck, the number of cells will identify 6v vs 12v. If the generator or starter has an oval tag on it, black is 6v and red is 12v. If any of your light bulbs have a number on it, post it here.
Check out the Tech Tips section for information about the 12v conversion.
