Diesel engines require on heated and compressed air to run efficiently. Glow plugs and intake heaters help make that happen, ...

While it's doubtful Plug will ever revisit its all-time high, it actually might be worth buying today as a contrarian investment for one simple reason: Its insiders are net buyers again.

Killian said they then moved onto the heads, which is where the glow plugs came into play. “This was really us with Cummins, but [we agreed] it’s time to get to glow plugs,” Killian told me.