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Old 07-13-2019, 10:30 AM   #1
mbiver
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Default 78 Scout II Rear Wiring Mess

Trying to get the rear wiring sorted out on my 78 Scout II but not really sure where everything connects to. Passenger side tail light still has the gang connector, but there isn't one on the drivers side, so looks like the previous owner did some "modifications". I've cleaned out the bulk head connector, applied some dialectic grease and re-connected. I pulled everything apart at the end of the rear wiring harness and tested each wire with dome, brakes, signals, hazards, headlights on/off, etc. Wasn't able to determine which wire energized the running lights. Diagram of what I found is attached. The typing was a little small in the overall diagram so broke it into 3 zoomed ones as well. Any guidance with how I can piece this back together is greatly appreciated. Thanks!
Attached Images
File Type: jpg Scout_Rear_Wiring_Harness.jpg (39.6 KB, 46 views)
File Type: jpg Scout_Rear_Wiring_Harness_Right.jpg (46.8 KB, 34 views)
File Type: jpg Scout_Rear_Wiring_Harness_Center.jpg (51.6 KB, 36 views)
File Type: jpg Scout_Rear_Wiring_Harness_Left.jpg (31.2 KB, 30 views)
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1978 Scout II with 1977 345 engine
Four wheel drive Dana 44 Axle's, Dana 20 T-Case, Power Steering, Power Brakes (Disc/Drum), no A/C.
Manual trans, Borg Warner 3-speed w/floor shift.
Prestolite distributor with petronix.
Fuel System: New 19Gal. Poly tank/Sending unit and Holley 2300 P/N 07448 kit from IHPartsAmerica, Nylon fuel line, relined original fuel neck filler tube.
Unknown non-oem modifications

Last edited by mbiver; 07-13-2019 at 11:32 AM.. Reason: Writing in the picture wasn't clear. Added zoomed versions.
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Old 07-26-2019, 02:50 PM   #2
mbiver
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Default Re: 78 Scout II Rear Wiring Mess

So I had 2 wires I wasn't sure about on my diagram. After doing a little more reading and testing I think I've identified one of them, and thereby the other due to elimination. On my diagram, the wire that does nothing when the key is off, but then once you turn the key to the "run" position starts a constant flashing no matter what scenario, appears to be the fuel sender ground. I ran it back to the passenger side marker light ground and once I tightened it down, the fuel gauge came alive. Not sure how that works, but whatever. So that means the one wire left is the tail light/running light wire. The wire will flash when the hazards are on and stay solid when the brake is also pressed, but I can't get it to work when turning on the headlights. I went to the bulk head connector and there appears to be 6 connections in there and then another wire joins the harness just after the BHC and goes to the back. I probed all the connections on the BHC and they appear to do what you would expect. Dome light, dome light switch, left turn, right turn, brake, reverse. Am I missing something or is the tail light/running light also supposed to come out of the BHC? Or is that the 7th wire that joins the harness just after the BHC the tail light/running light? Any assistance appreciated. Thanks!
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1978 Scout II with 1977 345 engine
Four wheel drive Dana 44 Axle's, Dana 20 T-Case, Power Steering, Power Brakes (Disc/Drum), no A/C.
Manual trans, Borg Warner 3-speed w/floor shift.
Prestolite distributor with petronix.
Fuel System: New 19Gal. Poly tank/Sending unit and Holley 2300 P/N 07448 kit from IHPartsAmerica, Nylon fuel line, relined original fuel neck filler tube.
Unknown non-oem modifications
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Old 07-27-2019, 07:19 AM   #3
Scoutboy74
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Default Re: 78 Scout II Rear Wiring Mess

I'll be referring to the FSM covering early SII models '72-74, but as it pertains to the rear wiring, I believe it should still be mostly, if not entirely applicable to your Scout as well. Beginning at the firewall connector, the circuits involved are as follows:

36-16 - Fuel gauge sender joins a connector near the tank with a brown wire that terminates at the center of the sender. A red wire is used as the sender ground.

57-16 - Right Turn/Haz/Brake corresponds to red wire of RH light housing.

56-16 - Left Turn/Haz/Brake corresponds to red wire of LH light housing.

71A-16 - Reverse light corresponds to black wire of of RH light housing.

71B-16 - Jumps the reverse light from the RH gang across to the LH gang, thus corresponding to the black wire of the LH light housing.

68A-16 - Tail/Park/Side marker corresponds to brown wire of RH light housing.

68B-16 - Jumps the Tail from the RH gang across to the LH gang, thus corresponding to the brown wire of the LH light housing.

One terminal of the gang connectors on both sides has an 18ga black wire which is the hot feed for the side markers. It derives that power via circuit #68, even though it is coming from an adjacent terminal of the connector. An 18ga white wire serves as the chassis ground for the markers on either side.

One terminal of the LH gang connector sends two 16ga wires out, a brown wire and a red wire to a connector, which then sends one 16ga black wire to the license plate bulb.

Circuits 63B/E are for the rear dome/courtesy coming down the RH side of the truck, but they do not terminate at the gang connector on that side, as they have there own terminations higher up inside the cabin.
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Coal Trickle - '99 Dodge Ram SLT 2500 Q-Cab SWB 4x4 - 5.9L 24V CTD/NV4500/8800# GVW/12K# winch
Hooty - '74 SII 4x4 - 392/TF727/D20/3.73 D44's/Spartan FA/Powr-lok RA/33g Fuel
Lemuel - '73 1210 Reg Cab 4x4 CS - 304/TF727/NP205/4.09 FA25 & 4.10 RA16/6800# GVW - "Pull Lemuel, pull!"
Organ Donor - '72 1210 Reg Cab 2WD - seized 392/TF727/7500# GVW - "Use my body to keep you alive!"
Mongo - '71 1210 Reg Cab 2WD - 345/TF727/4.10 RA17/6100# GVW - "Mongo love candy! Duh, huh, huh!"

Last edited by Scoutboy74; 07-27-2019 at 07:29 AM..
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Old 07-27-2019, 07:32 AM   #4
Scoutboy74
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Default Re: 78 Scout II Rear Wiring Mess

I forgot to mention that the early SII models used metal light housings which derived their ground via fastener and direct sheet metal contact. Your Scout likely has the all plastic housings which would thus require an additional wire to provide the chassis ground.
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Coal Trickle - '99 Dodge Ram SLT 2500 Q-Cab SWB 4x4 - 5.9L 24V CTD/NV4500/8800# GVW/12K# winch
Hooty - '74 SII 4x4 - 392/TF727/D20/3.73 D44's/Spartan FA/Powr-lok RA/33g Fuel
Lemuel - '73 1210 Reg Cab 4x4 CS - 304/TF727/NP205/4.09 FA25 & 4.10 RA16/6800# GVW - "Pull Lemuel, pull!"
Organ Donor - '72 1210 Reg Cab 2WD - seized 392/TF727/7500# GVW - "Use my body to keep you alive!"
Mongo - '71 1210 Reg Cab 2WD - 345/TF727/4.10 RA17/6100# GVW - "Mongo love candy! Duh, huh, huh!"
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Old 07-30-2019, 06:36 PM   #5
mbiver
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Default Re: 78 Scout II Rear Wiring Mess

Thanks a lot Scoutboy74. I do have the metal taillights that ground to the body when screwed down. Iíll study your
Info above along with the schematics in my manuals and see if I can figured it out. Looks like the front marker lights arenít working as well so I wonder if itís something as simple as a bad circuit in the light switch. In the meantime I have all the other lights working so at least I can drive around in the day time.
__________________
1978 Scout II with 1977 345 engine
Four wheel drive Dana 44 Axle's, Dana 20 T-Case, Power Steering, Power Brakes (Disc/Drum), no A/C.
Manual trans, Borg Warner 3-speed w/floor shift.
Prestolite distributor with petronix.
Fuel System: New 19Gal. Poly tank/Sending unit and Holley 2300 P/N 07448 kit from IHPartsAmerica, Nylon fuel line, relined original fuel neck filler tube.
Unknown non-oem modifications
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