found out the hard way that 6v motor craft plugs don't like glowing more than 5 second on manual switch. I had heard 15 second was the limit and also that various plugs can run forever with 12v so I didn't worry about it. My mistake...... My question is, ac delcos have the spade connector will they run just as good as the motorcrafts? I've heard they take 12v all day long and are just fine. Edit have researched quite extensively. Finding lots of contradictory information. Would like personal experiences on long lasting 6 9 glow plugs with manual control. Trying to set my buyer up right with my truck I'm selling. If the 6v motorcraft plugs are the best ill just tell him to be careful and not toast them like i did.