'67 800 Tail Light Harness routing and fuse location?

Discussion in 'General IH Tech' started by Scoutcamper, Jan 12, 2019.


  1. Scoutcamper

    Scoutcamper Farmall Cub

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    Hey all-

    I'm not having much luck with the search function. I was tearing into project Wilma trying to wire in my LED tail-lights and the PO had hacked up the wiring more than I thought. I'll be tearing a lot of that crap out tomorrow.

    I'm trying to find what the routing was for the brake / turn signal wires, between the brake switch at the pedal and the back of the vehicle. I also understand that there should be an inline fuse somewhere in there? I'm hoping the original wiring is still there and usable, or at least I can use it to pull good wire through the correct routing.

    The brake lights had been re-wired from the switch at the pedal with a new wire section running under the floorboard and zip tied to the frame. This ran to some cheapie harbor freight lights mounted to the bumper.

    The good news is that the running light circuit was still wired to the stock housings and functional at the bulbs, so I'm sure there is a good ground.

    Edit: Also, the turn signals are working in the STOCK housings. They don't appear to be wired to the cheapie harbor freight setup.

    Thanks,
    -Josh
     
    Last edited: Jan 12, 2019
  2. kevingweq

    kevingweq Y-Block King

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  3. Scoutcamper

    Scoutcamper Farmall Cub

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    Thanks! I had previously found the circuit diagram, but it does not tell me where the wires are physically located (routing vs. diagram).

    -The fact that the turn signals are working tells me the wiring should be OK between the column and the rear, if it's the same circuit as the brake lights.
    -The fact that the wired-in cheapie lights at the bumper work tell me the brake switch, and power to the brake switch, should be good
    -So by elimination my problem should be missing / damaged / disconnected wiring between the brake light switch at the pedal and the turn signal switch in the column, correct?

    Is there a fuse in this section of wiring?
    Edit- the only fuse I'm seeing in the wiring diagram is a 14A inline fuse on the Flasher circuit, but I can't tell whether the Stop Light Switch is powered through that circuit or not.

    Any other theories?

    Thanks,
    -Josh
     
    Last edited: Jan 13, 2019
  4. Scoutcamper

    Scoutcamper Farmall Cub

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    I found what I'm guessing is the correct terminal connector to plug into the stop light switch:

    The fuse was a 30A and appeared to be good (not blown). Tried plugging it into the stop light switch- no magic smoke or any other effects inside or outside the cab, with brake pedal depressed or released.

    20190113_123854.jpg

    Here's the stop light switch with the wire from the PO in place. Note the second connector on the switch matched the one shown in the first pic. I have not unplugged that connector at all, I'm assuming it's Key-off 12v, will measure tomorrow. And no, I did cut the "access slot" in the dash.:
    20190113_120508.jpg
    I'm guessing this guy is the 6-way connector from the steering column? Any ideas on the bare yellow wire or the blade-terminal red wire?
    20190113_124010.jpg
     
  5. scoutboy74

    scoutboy74 Lives in an IH Dealership

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    A 30 amp fuse seems excessive for brake light circuit protection, when you consider the typical size fuse found in IH vehicles is 14 amps for the vast majority of fuse protected circuits. It appears that some, if not all the circuit numbers within that green wire gang connector are legible. Identifying them might prove helpful. Any wire that you can still read the number on is YOOGE. As for the loose yellow and blackish/red, they were probably connected, but that is admittedly an assumption based only on the fact that they appear to have been terminated in close proximity with no other likely choices visible.
     
  6. Greg R

    Greg R Dreams of Cub Cadets

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    The fuse under the dash was for the flasher and is 4 amp. All voltage for the signal and stop lights is sourced from the hot connection on the end of the light switch. It goes like this: For the stop lights the voltage starts at the light switch hot to the brake light switch. From there it goes to the connector and from there to the red wire on the turn signal switch. At center position of the T/S, the stop lights are connected to the red wire. At the T/S Brown is left rear, and Green is right rear to the lights. Do you have a 4way hazard switch?

    For signaling: from the same live end on the light switch the power goes to the 4 amp fuse, then to the SignalStat or flasher. From there it goes to the connector and then the black "center" wire on the T/S switch. Moving the turn signal arm moves the contacts to switch voltage source for the side selected; from the brake light switch to the flasher and energize a front light.

    Any numbers still readable on the wires? I vaguely remember, or it's possible, the YELLOW wire was for the horn button in the steering wheel assembly.

    For trailer lights all that was needed was to splice into the Left and Right wires behind the bumper with a pig tail to a trailer plug connector.
     
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  7. Scoutcamper

    Scoutcamper Farmall Cub

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    Thank you! That confirms what I thought I was seeing based on the wiring diagram. With the fact that there was a 30A fuse in that line, plus some of the wiring looking a little "toasty", I'm now almost certain there is a short somewhere between the headlight switch and the turn signal. I'm guessing why the PO bypassed that circuit.

    Based on this I will probably replace the 30A fuse with a 4A and see if I can get things working. If not, I think I'll splice into the "new" circuit for brake lights until I can get in the parts to put in a new turn signal switch and flasher and associated wiring sections.

    EDIT: Had another thought, though: My turn signals are working. If this fuse is not hooked up, my turn signals should not work, correct?

    Thanks,
    -Josh
     
    Last edited: Jan 16, 2019
  8. Greg R

    Greg R Dreams of Cub Cadets

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    It does kinda read like the fuse is some how bypassed or maybe a back feed from somewhere.
     
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  9. Scoutcamper

    Scoutcamper Farmall Cub

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    Hey all-

    Finally got my tail lights back to semi-functional and setup for my LEDs.

    As I mentioned above, I had brake lights functional through a stand-alone circuit set up by the PO using trailer brake lights to bypass the existing brake light circuit.

    The turn signals and running lights were working at the stock buckets.

    Rather than have the scout torn up right now to troubleshoot and fix the existing harness, I opted to splice the stand-alone brake circuit back into the stock buckets / LEDs, with the understanding that the "brake" signal would over-ride my turn signals when I hit the brakes.

    What I did not take into account was the fact that the stand-alone brake circuit signal would back-feed through the stock turn signal circuit and turn on ALL the lights when I hit the brake.

    After a little down time to cool off, I realized that I could still use a brute-force approach and isolate the brake signal to just the tail lights.

    I bought 4 Schottky Diodes (also called Rectifiers) rated for maximum 6A / 100V. These were about $2 / each at Fry's Electronics.

    I soldered a Diode inline with the stock brake / turn signal wiring, with the Cathode Band (stripe on the body) facing toward the tail-light. I then spliced in the connection to the stand-alone brake circuit BETWEEN the Diode and the tail-light.

    This isolated the turn signal circuit in one direction, making it so the brake signal could not backfeed through to the steering column and turn on all the lights.

    It did not completely solve the problems- I found that I also needed a diode on the brake signal line, because the turn signal was backfeeding through to both tail lights.

    With a total of 4 diodes in place, 2 per side, I was able to isolate each tail light and have a semi-functional solution. I just need to remember that my turn signal will "turn off" at the tail lights when I hit the brake, since the brake signal will hold the light on solid instead of blinking. Pics / diagrams to follow.

    -Josh
     
  10. Scoutcamper

    Scoutcamper Farmall Cub

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    OK, here's the diagram. Any Electrical Engineers on here please forgive my scribblings and possibly incorrect description, I'm a Mechanical guy.

    20190129_221925.jpg

    For anyone not in the loop, a Diode is essentially a one-way valve for electricity.

    The 2 types of Diodes you will commonly run across are Zener and Schottky. My understanding is that the Schottky type has lower voltage losses and can generally withstand higher current ranges, so that what I looked for.

    When you wire them up, you want the Cathode band- the stripe on the body- to be closest to the part you want the electricity to flow to.
    Here's what the actual parts look like:

    20190127_132531.jpg

    You can see the actual part above the box in this pic, I'm in the process of soldering it into the circuit.
    20190127_133136.jpg

    -Josh
     
  11. Scoutcamper

    Scoutcamper Farmall Cub

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    The important take-away to this is:

    YOU CAN MAKE A TEMPORARY WORKING BRAKE LIGHT FIX TO BYPASS THE DASH / STEERING COLUMN WIRING AND STILL KEEP (SOME) TURN SIGNAL FUNCTION IF YOU SET THIS UP.

    EDIT: You would disconnect the wire running between the brake switch at the pedal to the steering column, and plug in a new wire, run it to the back of the Scout, and split it off to the 2 tail lights. This is labeled as "Trailer Light Brake Circuit" on my diagram.

    -Josh
     
    Last edited: Jan 29, 2019
  12. kevingweq

    kevingweq Y-Block King

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  13. Scoutcamper

    Scoutcamper Farmall Cub

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    Very interesting. I'm guessing they have some internal circuitry that solves the problem of the brake light signal over-riding the turn signal blink.

    I may give it a try if it looks like the solution for my under-dash issues is super time consuming and / or expensive.

    -Josh
     
  14. Greg R

    Greg R Dreams of Cub Cadets

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    I'm too "Old Skool" to gussy up work arounds.

    The schematic shows that the brake switch output DOES go through the turn signal. The rear bulbs are dual element. The same element for turn signal IS the brake light on both sides. The turn signal switch switches to power from the flasher for flashing on the side selected. If ALL the lights are lighting with the brake switch, front and rear?, then there's a bad turn signal switch, bad 4 way flasher switch or crossed wiring. Band Aiding with diodes doesn't fix the problem. Rip out what isn't stock and make it right. KISS
     

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