What is this wiring piece?

[ray_mcavoy]

^^ Yes, they're fusible links.

To be more specific, the fusible links are actually the short sections of smaller gauge wire between the starter solenoid and the off-white plastic "tubes". The "tubes" are just insulators covering the factory splices between the fusible link & the wire it protects.

Here's some more info on fusible links --> http://www.madelectrical.com/catalog/fusible-link.shtml