Trouble shooting the Rheostat

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  1. #1
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    Trouble shooting the Rheostat

    Hello y'all. First post here :-) I have an '83 5-speed terracotta warrior.

    The 15 volt tail fuse behind the battery keeps blowing. The previous owner apparently removed the front side indicator lights already - there's just a hole and no wires to be seen so I can rule those lights causing the fuse to blow. So I kept searching the forums and found a thread called Temp Rheostat Fix about disconnecting the Rheostat wires switch under the steering column and using a fuse to get things working again.

    I have opened up the lower part of the dash under the steering column to get to the Rheostat and I disconnected it. But I need a 'tiny' fuse as the normal sized ones don't fit. So what voltage 'tiny' fuse do I need until I get the $ for a new Rheostat? I'm just trying to avoid getting a ticket since I leave for work in the early AM hours so it's pitch black outside and the tail lights only light up when I brake.

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  3. #2
    CelicaSupra.com Member Road Ripper's Avatar
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    Rheostat would not affect the taillights unless it is shorted to ground somehow, and disconnecting it would make the taillights work again. The parking lights, taillights, radio lights and dash lights are all fed on the same circuit. If your front marker lights are missing and one of those wires is touching metal, it will short out the circuit and blow the fuse. Then you would not have dash lights or marker lights. If the other lights on the circuit still work, then the metal bulb holders in the taillights have probably rusted and prevent the tails from having a ground, so they use the brake light circuit ground and work with the brake lights. This is a common issue with our cars.

    Keep rocking the terra cotta; it's one of those unique colors that seems to be underappreciated.
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  4. #3
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    Ok, put in another fuse with the Rheostat disconnected and started the car and turned the lights on. This time I did not see the dash light up. The fuse must have blew immediately whereas before it the dash lights would come on as usual and it would take a minute or two for the fuse to blow.

    Then I took the covers off the taillights and looked at the wiring, bulbs, bulb holders, etc. and everything looks like it was installed yesterday. I do not see exposed wiring anywhere or anything that looks off.

    So I unhooked the battery and pulled the fuse box yet again and I still dont see anything that looks out of the ordinary. I'm stumped. Any ideas on what to check next? I really want to drive my '83!

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  6. #4
    CelicaSupra.com Member ddd228's Avatar
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    That 15 A. fuse protects a lot of circuits.
    The rheostat may be shorted to ground as is other circuits,including the license plate light,glove box light,etc.
    http://www.cygnusx1.net/Supra/Librar....aspx?S=E&P=15
    This is for an '85.
    Dave in Seattle. I keep LATE hours.Hidden Content
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  7. #5
    Boosting Mod SilverMk2's Avatar
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    You should really have the Toyota factory EWD if you really want to troubleshoot this correctly. The tail fuse wires pretty much every light bulb in the car except the taillights so the wires literally go everywhere. There is a large junction box in the left kick panel. The wiring from the engine bay fuse box runs from there to this interior junction box. At least on 85 the circuits for the tail fuse runs thru connectors 2A, 2B, 2D, 2G, 2H, 2I, and 2J to the components. What I would do is unplug all those connectors and one by one plug them back in til the fuse blows. This way you can identify what circuit its on and troubleshoot done from there. More than likely what you'll find is something wrong where someone hacked something up at some point like an alarm or something. The rheostat is just a potentiometer between the dash lights and the ground, so even if was shorted about all that would happen is your dash lights would be full bright.

    HTH

  8. #6
    CelicaSupra.com Member drjim's Avatar
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    What I would do is unplug all those connectors and one by one plug them back in til the fuse blows.

    And THAT, my friends, is called intelligent troubleshooting!

    Simple, concise, and practically foolproof.....

    - Jim
    1985 5-speed "Ms. Swan"

    OH, What A Feeling!

  9. #7
    CelicaSupra.com Member ddd228's Avatar
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    I have a photo of my screen for an '82.
    Can you see any of this?
    http://i514.photobucket.com/albums/t...m.jpg~original

    [IMG][/IMG]

    Click on photo for a larger image in Photobucket.
    Dave in Seattle. I keep LATE hours.Hidden Content
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  10. #8
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    I. Am. An. Idiot!

    So I got ready to trace the wiring diagrams and I started taking apart the area under the steering column for the 3rd time for easier access the the drivers side fuse box. I was following the diagram above and also cross referencing then with the 1983 repair manual (the one from Toyota with the green cover), when all of a sudden I realized I never laid eyes on how the the indicator light wiring was removed

    I realized I needed to get to the indicator light wiring from under the wheel well area and *not* by just removing the orange light coverings and looking inside the space. So I turn the wheels and remove the wheel well covers and low and behold there was what remained of the former indicator lights and exposed wiring on both driver and passenger side. I believe the passenger side wiring was the culprit since the light fixture crumbled in my hand. So I used electrical tape to tape off the exposed metal terminals and now my dash and running brake lights are back to normal! Whew!

    I feel so stupid and should have been more thorough in checking for the indicator light wiring before moving on to other, more laborious things. But, I know a lot more about my '83 than before so that's a good thing :-)

  11. #9
    CelicaSupra.com Member drjim's Avatar
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    It's called learning.

    I screwed up so much stuff when I started working on cars I stopped keeping track of what my Screwup Of The Week was.

    But I got better and better, and you will, too.
    1985 5-speed "Ms. Swan"

    OH, What A Feeling!

  12. #10
    CelicaSupra.com Member
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    I believe the actual philosophy is, "Make all the mistakes you can as fast as possible". Of course, you don't want to make a mistake that ruins everything in an instant. Well, unless you're using a video camera to record "the event" for the enjoyment of all mankind! In that case, it would be wise to take appropriate precautions so you're ultimate demise isn't recorded at the same time. If the worst does happen, at least you won't be accused of being a failure at committing suicide!
    But seriously folks, these type of things stay with you for life. They're the kind of things that we just can't forget. For example, the reason I haven't tried to fire up any motors for the first time without securely tightening the distributor down stems from an incident nearly 40 years ago when I was building NASCAR motors. I leaned over the carb just in time to greet a fireball coming up. The next thing I remember is the owner / driver laughing his ass off inside the car and wondering what the weird smell was. (It was burnt hair.) Nearly all of my beard was gone, the same for my eyebrows, too. And I had no eyelashes at all! From that day forward, even I thought that laughing hysterically was totally appropriate.... at first. But I added that should the victim still be on fire, it would be nice if any and all observers tried to put them out... So should you ever wonder what happens when the ignition fires before the intake valve closes, just remember this. To this day, the vivid memory of "the event" is "burned" into my memory!
    So relatively speaking, being a genius qualifies me to overrule your own personal assessment of being an idiot. If you were an idiot, you wouldn't know it. So therefore, you can't be an idiot if you realize that you learned a valuable lesson here. The even better news is that not only do you have a good story to tell for the rest of your life, the lesson you learned will save you a tremendous amount of time in the future. And you know way more about your car than you did. There's no downside to that either!

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