sounds like your "tilt" switch is gunked up. Run a patch wire across the leads, and see how it goes.
With any miles or weather, from what I hear, its common. They are a simple engineered device. Its under the ECU cover, in front of the rear tire. I've ran across a couple of those tilt switches that were really gunked up
OR,
Could possibly be the other ends of your battery cables. The ground from the factory goes straight into the top of the engine casing, behind the faux oil tank. Most of the X's on assembly, had a lot of loc-tite put on that very bolt, the battery grounds to. Take it out, and run a wire brush on it, to clean the threads. If you got one, use a thread cleaner where the bolt goes.
AND,
One of your relays could be going bad. There are 3 of them behind the faux oil tank cover, on the battery inside wall. Most parts houses carry them, and they are not terrible in price. Take one with you, so they can look at it. As the prong patterns do change up a bit vehicle to vehicle. It'd really help if you had a schematic, so you'd know what you're looking at. Down load it.... and print it off.
Give those a shot.... come on back with your results... If I can't answer, I know who to find out from. good luck
