Wire for oil sending unit/gauge cannot be found...help!

[dans78c10]

There is a lot of posts about gauges, I searched, apologize if this has been answered somewhere already.

78 C10 350V8 with gauges on dash.

I am looking for the wire that will go to the oil pressure sending unit located at back of engine on china wall.
Looked through a 78 wiring diagram, no luck. AI summary (dummary) suggests a tan wire for oil, and dark green for coolant send unit.
There is a dark green wire (cut off, no connector on it) coming out of the large harness that runs across the firewall behind engine. At the same point on the harness is the wire that goes to the batt. side connector on the distributor. Also at the same point there is a dark blue wire (cut off, no connector on it) that exits there... could this be for the oil sender unit??

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I peeled back the cover a bit for this harness, they attach at the block at the firewall, to see the wires and colors.

 

[goldpack]

I guess you mean Fire Wall, and not China Wall.

did you try a factory service manual on charm.li (typically cited on forums).

Free Car Service Manuals from Operation CHARM — No strings attached!

Operation CHARM provides completely free repair/service/workshop manuals for over 50,000 models of cars and trucks manufactured 1982-2013. No sign-up or paywall.

charm.li

more are on their newer site

Free Car Service Manuals from LEMON Manuals

LEMON Manuals provides free repair/service/workshop manuals for about 10,000 US and Canada market vehicles from 1960-2025. No sign-up, no paywall!

lemon-manuals.org.ua

when I have looked they don't have them in color ,...just black and white scans.
(but one might have the wire listed by color)

 

[dans78c10]

Goldpack, I did mean china wall. There is a threaded hole that a 45 degree angled fitting threads into. The oil sending unit then threads into this. Then a wire attaches to the sending unit, which I am not sure about.

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I have a service manual, lots of good info but no wiring diagrams for this situation.
I downloaded a PDF of a 1978 wiring diagram from a post on the forum, it was not much help, and I am pretty good at reading/using these diagrams. I will look into the diagrams you linked. Thanks.

I took the loom/cover off of this set of wires hoping to find a tan wire hiding in there. Only wires exiting are the green, blue, and distributor wire.

I want to get all of this engine bay stuff wrapped up while the fenders and hood are still off (much easier to get around in there at this point). I have everything painted and am eager to get this truck put back together.

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[Turbo4whl]

Newer year truck manuals have color diagrams. Older manuals may have letter codes for the colors, ie, DB-dark blue, LG= light green etc.

 

[Turbo4whl]

Your book, page 6D-40

Fig 6D-2-Diesel Electronic Control, near the bottom of the picture. Oil pressure sender dark blue wire, temperature sender dark green.

Some times the factory repair books don't show what may be in an earlier book. Your book, I can't find the gasoline engine wiring diagram.