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I am trying to decipher the wiring diagram and wiring harness.
Question about some things on the diagram.

Referring to wiring diagram from TM 9-8012

Wire # 28...... is that wire connected to the fuel gage and fuel sender?
If so, where does the power come from?

Wire # 36........I can tell that wire is connected to the oil pressure sender, and I suppose that 36 is connected to the gage on the other end.
If so, how does it get power?

Same goes for wire # 33 to Temperature sender.

And if I use a solid state regulator.......Does -9 & + 8 go to the volt meter?

Ken,

Check out the section in the same manual about the instruments and gauges. This section has a rear view photo of the instrument cluster and the text for the instrument cluster is very good.

Power to those gauges is supplied by the instrument harness which is wire "27". The "inside" terminal of the fuel, oil and temp gauge connect to the gauge wiring harness. The "outside" terminal on those gauges connect to the sending units.

Greg

That's the infamous SPIDER harness that takes power from #27 and distributes it to each of the three gages.



The 4 wire spider "AA" connects three of it's wires to the sender equipped gages and the fourth wire "T" connects to # 27 from the ignition switch.

The 8 & 9 wires are for use with an amp meter. If you use a solid state regulator they are not used. You must install a volt meter (Generator Condition Gage) and connect it's + connector to a 24 volt source. The cleanest way to do this is to use a big M series truck 5 wire instrument power spider and use the 5th wire for your voltmeter.



Here's one source. This is the late Packard type but can easily be converted to Douglas.

http://saturnsurplus.com/electrical/instspider.htm

Thanks, It' very clear now.
I thought maybe that wire 27 was the power, but wasn't that sure.

And my spider harness has 7 pig tails.