ski522

A break wouldn't blow fuses; it would have to be a short. I find it odd that two wires would somehow short under electrical tape unless they are being twisted or pulled on at a common point, like the harness getting pulled when turning the steering. I found a circuit diagram that might help. I'm not sure of the year, but I doubt it changes much.

One way to troubleshoot is to use a multimeter with a continuity setting. Put the black lead on ground, then use the other lead on a plug to see if it grounds out when it shouldn't. This isn't a perfect test if a relay or other component needs to engage to complete the circuit, but it's a good start. Make sure the battery is not connected when doing this too to be safe. 

https://www.manualslib.com/manual/830446/Yamaha-Yfm-400-Fwa-P.html?page=33#manual

Good find. Electrical problems can be such a huge PITA, though on ATVs they're not as bad as on a car.

I don't recall, but I think you're right that the starter requires something bigger than a 10A fuse. But if it ran and then died, I'd be more concerned with gas, assuming it's fresh. If it is, then I suspect stuck floats in the carb. Remove a side and tap lightly on the bowl, it should help free it up. Otherwise, your carb probably needs a good cleaning if it's been sitting for a year with gas in it.

Thanks for the idea as well. 

Capacitors do not have infinite life, and as an EE, I question the claim of 10x the service life over a jumper pack. Maybe, but I think I'll just stick with a jumper pack. I've been happy with my NOCO Boost GB40, going on 6 years and still strong. That thing started my Vette with a DOA battery, so the ATV is a piece of cake when I've needed it.

My 2007 has been pretty reliable, though some crap got into the carb throttle assembly and I just had to replace it, but otherwise the machine has been very reliable.

Friends had them, and I always wanted to ride with them since we had lots of trails. Sadly, southern NH isn't so friendly for riding anymore, but we do have Jericho State Park up north, though it's a 2-hour drive from the NH seacoast.

Bought a electric 1800psi pressure washer at Lowe's for other projects for around $100...but works great on the ATV caked in mud..spray Simple Green on beforehand and pressure wash off mud and grime.