Electrical woes on 79.....

Discussion in 'Ranchero Tech Help' started by drlance, Jul 31, 2014.

  1. drlance

    drlance In Fourth Gear

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    Robinson, IL
    On the way home last Wednesday evening, I stepped on the brakes and had the entire electrical system short out for a second. This happened 3-4 times and then stopped. This only occurred with the headlights on. Upon arriving home, I found that I do not have rear side marker lights or rear tail lights or license plate light, but the front side marker lights are lit. Brake lights work fine, backup lights work fine, turn signals work fine.
    I took apart the tail lights, checked for shorts and found a loose ground on the passenger side, fixed it, no change.... I have managed to fix the Key in column buzzer and the horn, but still no tail lights.
    I replaced the headlight switch.... no change ( Note: The Autozone switch is WRONG!!! The O'Reiley switch is the correct one!!!)
    I do need some color code help. My manual doesn't give wire colors.
    What color wire is the power for the rear sidemarkers on a 1979 Ranchero???
    Also, I found a blown fuse in the lower right hand corner of the fuse block, the writing is worn enough not to be able to read it. It had a 30 Amp fuse in it. If I replace the fuse I get the shorting out with headlights on and stepping on the brake. With it removed, the car runs fine and all the lights and accessories still work.... Weird huh? So what is the fuse for, again my supposed repair manuals do not show a fuse block layout....

    Thanks for any help you can offer, I just need to find the open wire!!!
     
  2. ribald1

    ribald1 Banned PLATINUM MEMBER

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    I suspect you will find the problem in your steering column wiring or emergency flasher switch.
     
  3. Hillbilly

    Hillbilly In Maximum Overdrive

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    Do you still have dash lights ? Dash lights feed off the same fuze as the tail lamps then thru their own 5 AMP fuze. Tail light wire should be the dark brown wire in the bundle to the rear. Your tail wires should run down the driver's side under the sill plate under the door then thru the rear quarter panel. I would check for insulation damaged by a screw in the wrong place or the wires rubbing on a sharp edge. Trailer hitch ? Many times that added wiring is a problem.
     
  4. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    The brake and marker lights have their own filaments in the bulbs; with the headlights on and you step on the brakes, bad filaments even in one bulb cause a cross-circuit short. Sometimes, when you step on the brakes with the headlight switch off, the front markers light up due to the crossed circuits. Pull one side's bulbs, replace the fuse, and see if it blows. You have a 50-50 chance of finding the bad side the first time.
     
  5. ribald1

    ribald1 Banned PLATINUM MEMBER

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    A cross circuit short on a single source DC system?
    This electrician has a hard time seeing how that could blow a fuse.
     
  6. 72GTVA

    72GTVA Administrator Staff Member

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    Hmmmm... it was mentioned above but I'll throw my hand-grenade in the punchbowl... a whole bunch of the wiring that is involved in all of this is located/routed through the turn-signal switch... might be time to be looking at that which contains the emergency blinker switch and assorted and sundry other exterior lighting/functions...
     
  7. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    As an ASE-certified Master tech with 8 years certified and 20 1/2 years total automotive experience, not to mention a Navy-trained guided-missile Fire Control Technician, I have seen some of the weirdest electrical s#!t in cars that make you go "How'd that happen? As for your comment on single-source DC systems, Ribald, what matters is what the new current path is; a backfed circuit will blow a fuse if the current exceeds the fuse rating, or cause any number of electrical gremlins if it doesn't. Sometimes electricity just does what it does, not necessarily what you want it to do. And I did consider the T/S switch, but the bulbs are the simplest possible cause, so I directed him to check them first.
     
  8. ribald1

    ribald1 Banned PLATINUM MEMBER

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    I will leave this one alone.
    I specifically do not discuss my training, certifications and experience as what I do speaks for itself.
     
  9. Hillbilly

    Hillbilly In Maximum Overdrive

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    Awww, be nice, guys. Let's asume his brake lights and turn signals have no cross connections, either by filament, or by bad switch or wiring. The shift indicator light in the column ( light blue with red stripe ) would be the most likely culprit if you follow that the dash lights and their fuze get powered by the taillight fuze. Chafed wire in the column ? Really suspect if he has a tilt column. Just something to check. Whatever is really happening sounds like a direct short to ground.
     
  10. Clark

    Clark In Maximum Overdrive

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    drlance: Be darned sure to check your grounds. All kinds of weird crap happens in these Rancheros with bad grounds as power feeds back in strange ways.
     
  11. drlance

    drlance In Fourth Gear

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    Started checking things this weekend, got sidetracked by Granddaughter's birthday......


    4 ways work, turn signals work brake lights work..... Going to pull the bulbs next and start looking for shorts to ground... someone, sometime, did a 'splice' behind the driver's seat where the harness goes back into the drivers side fender..... Will start there since it most likely isn't 'factory' (It's spliced with wire nuts and black tape.....) Thanks for the ideas!!!
     
  12. handy_andy_cv64

    handy_andy_cv64 In Maximum Overdrive SILVER MEMBER

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    Black tape is OK, wire nuts...no so much.... X^((
     
  13. 72GTVA

    72GTVA Administrator Staff Member

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    This post is absolutely guaranteed to start a pissing contest (again) - but here is the Ford Recommended Repair Method for 14 gauge (what our cars use in lighting distribution) and smaller:
    Ford Solder Method1.jpg

    Ford Solder Method2.jpg

    Ford recommends using a ratcheting crimp tool for AWG 12 and larger.
     
  14. 72RancheroGT

    72RancheroGT In First Gear

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    Would bad ground also cause one headlight to be bright and the others really dim?
     
  15. 72GTVA

    72GTVA Administrator Staff Member

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    Yes, possibly. Each side of the wire harness has a ground ring connector that screws to the radiator support. I'd check those first.
     
  16. 72RancheroGT

    72RancheroGT In First Gear

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    Awesome I appreciate the help. How about front turn signals. The previous owner removed the housing and all. There are some plugs ( both with two connectors but one is small and one is about a half inch wide) on the firewall. Would this be what I'm looking for?
     
  17. 72GTVA

    72GTVA Administrator Staff Member

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    Firewall or radiator support? Below is the harness removed, the turnsignal light connectors are quite close to the marker light sockets in the harness and installed are near the front of the fender, usually sticking through an access hole leading down towards the front bumper... '72 lighting harness.jpg
     
  18. drlance

    drlance In Fourth Gear

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    finally got time to take the Ranchero apart. Both the Orange w blue stripe and the orange with green stripe wires went to ground. I opened the splice for those wires and the short from cab to backend disappeared. Took the column apart and removed the Turn Signal switch. Once unplugged the short on the forward portion of the 'splice' disappeared in both wires. Have ordered a new turn signal switch from Dearborn, although I can't find a chaffed wire, but one of the metal tangs for cancelling the turn signal is missing, Lord knows what it did on it's way to the floor and probably into my shopvac...... as a note, I do not have a tilt wheel, so I figure something went nuts in the turn signal switch. Thanks for all the help!!!

    Lance E. Sikorski D.C.
     
  19. mo.herbfarm

    mo.herbfarm In Maximum Overdrive

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    Despite all the wrangling in this thread, I have to state that, there is no "f''ing magic" involved with, or happening in, vehicular wiring systems. All the circuitry is put together using basic circuit theory, and thus, can be analyzed and trouble-shot using that same theory.

    Two turn signal filaments, for example, being fed by a single fuse, are invariably in parallel with each other, even though they are switched individually in turn signal use, since those same two filaments are BOTH fed power as brake lights (but not in ALL designs). Please explain how one of those filaments could become short-circuited and affect the opposite side's filament, other than to blow the fuse.

    If one filament somehow short-circuited to ground, a rather misleading statement, since one end of the filament is already connected to ground the fuse would blow. If the filament partially shorted several of it's coils across one-another, the current flow would increase, the remaining coils would glow brighter, and depending on the portion of coils no longer a part of the original length of the filament, the fuse might blow, or alternatively, if not, the filament would likely quickly get much too hot, melt, and open the circuit.

    Or, maybe I'm full of crap! Tell me! mo.
     
  20. burninbush

    burninbush In Maximum Overdrive

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    No, you're exactly right about the current flow. I've never seen a shorted bulb, but it's worth mentioning that the wires inside the bulb to which the filament is attached are much smaller than the external wires feeding the bulb, so even if you put in an oversize fuse the wires inside the bulb would melt before the wire in the circuit feeding it.

    Not sure about other brands, but in the years of Ranchero, the brake and turn-signal are both using the same filament. The brake signal is in series with the turns flasher, so if the brake is on, it is interrupted by the flasher. At the front the turn signal has its own dedicated filament.

    Trying to understand the details of the turn-signal switch assy under the steering wheel has been known to drive men crazy. Best to just replace it if suspect.
     
    mo.herbfarm likes this.

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