Here is where I found the cause of the fire.
This battery cable was rubbing against the hold down bar, wore through it's insulation and shorted to the bar.
This is a problem because this Sparrow had the Pack Negative tied to the frame/12v ground.
The power flowed through the front famework (which appears to be isolated from the rear), then through the brake line to the back framework, which is tied to pack negative through the controller.
