It's located behind the left cylinder accessed through the starter cover, #24 0n page 23 of the owners manual referenced earlier. You will have to remove the generator to change it out. I just removed mine (Q 55-G) 2 weeks ago for other reasons. You will need a jack system to lower it down and then roll it our from underneath. They are not that heavy, maybe 200lbs and two men can pick it up. I used a motorcycle jack stand with rollers, worked great. I have not changed a starter, but should be obvious once you see it.
Before you do this though, check all things in the trouble shooting sections first. I bet you have a bad connection on the battery cable and more likely the grounding cable on the generator frame or on the chassis frame. Clean both ground connections and tighten both good.
John & Clare - Buck & Zeus - Jack & Husky
2008 Fleetwood Bounder 38P
Towd: 2 HD Streetglides