MEP-802a DN2M heater plugs

[cscott719]

Hi.

I picked up a DN2M engine that is used in the 802a TQG. The question I have is regarding the heater plugs in the air intake manifold. According to the wiring diagram, these plugs are wired in series. However, I don't know how that would work, because the plug simply has a single screw terminal on top of each one. If there were 2 terminals, that would make sense.

I suspect the plug is grounded through it's body to the intake manifold. If this is true, and a wire is placed under the screw terminal lug from one plug to the other, and then connected to the heater relay, that would effectively put the plugs in parallel, not series as the diagram in TM9-6115-641-24 would suggest.

Does anybody have any insight on this? Perhaps a photo or two showing the wiring? Is it possible that the TM is incorrect? If the plugs are indeed wired in series, and one of them failed, it would prevent the other from working too. In my mind, a series setup would be illogical, because in case of a failure of one plug, the engine would be nearly impossible to start in cold weather. In a parallel wiring, one plug failing would not prevent the other from operating, thus "possibly" allowing the engine to start, since there would be at least some heat applied to the intake.

Thanks!

Scott

 

[TooMuchWork]

The wiring diagram is correct as the intake manifold heater plugs are not individually grounded to the manifold. On an installed generator the positive lead carries 24 volt to the (2) 12 volt plugs in series and the latter plug has a wire going to one of the bolts that the a exhaust flange is mounted to the intake manifold. Sorry as I can not provide a photo at this time. Hope this Helps.

Brian

 

[cscott719]

Thank you Brian. Perhaps my confusion is coming from the appearance of the plug terminals themselves, since I have never seen this engine in any form with a wiring harness on it. On the attached photo, the plugs have a screw terminal at the top with a thumb wheel type nut on them. My assumption is that these nuts are removed, and a wire, with perhaps a ring terminal on the end, is secured under the nut. That takes care of one connection. But where is the other connection made?

Thanks!

Scott