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Thread: Identify that mystery part - electrical doo-dad on Jeep

  1. #1
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    Question Identify that mystery part - electrical doo-dad on Jeep

    In the process of cleaning up the spaghetti of wires but I dont want to introduce new problems if I dont understand whats going on and start disconnecting stuff.

    I have already ruled-out it being a henway or a dikfur.

    Alternator is a 12volt conversion, its a 3 wire alternator and the first thing connected to the output batt wire (as it goes on into the dash, to reach the ammeter gauge) is this isolated cylinder object. On it, one wire going from the alt is attached to the wire tab on the lowest end, and then there is a clamp where the other wire is then attached and then the wire leads to the ammeter. These are the only 2 wires attached to it.

    The voltage leaving the alternator is 17.5 volts and when measured at the clamp leaving this cylinder thing is the same 17.5 volts. There is a terminal on the other end of the object that nothing is connected to, that when I read it there, I get 15.5volts. There is live voltage exposed across the entire metal surface of the cylinder, and you can see there are rubber isolators on both ends so the the voltage doesnt ground out on the brackets. You can tell by the patina its been there quite a while.

    I dont want to pull it out or bypass it if I dont know what it is, but 17.5volts is concerning and if this thing isnt serving a purpose Id like to get rid of it. Not sure if there is fusible link in the wiring yet, there are no fuses on the vehicle, just circuit breakers for the few electrical items there are.

    (BTW When I measure across the battery tops, vehicle running, I get 14.4volts )

    My only guesses at this thing is some sort of industrial voltage reducer (and its not hooked up right) , or a + voltage bus bar, or some kind of weird circuit breaker, again possibly industrial ? I dont think its automotive, maybe its a tractor part or ?

    I have googled and not come up with anything that I can identify this. Figured one of you guys might have seen something like this before

    about 5/8" diameter and 8" long. What the heck is this thing ?





    Last edited by Robb; 03-29-2017 at 11:17 AM.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  2. #2
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    Definitely a Flux Capacitor.... you should be fine as long as you don't exceed 88mph which should be easy. :=)

    Never seen it. I don't have that on my XJ.
    99 XJ, 33s GY MTR, RK LA Kit

  3. #3
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    That looks like an old high-power variable resistor. While hard to tell from the pictures, the cylinder part would be brown ceramic and then there would be a strip of exposed wires that the clamp connects to. I can see the exposed wires towards the fender in the third picture. It would be right at home in a 60's TV transmitter.

  4. #4
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    The whole outside surface is metal and just kinda rust colored. (Edit, maybe not, but I swear it conducted voltage when I hit it with the meter)

    the second picture is likely the best overall view of it.

    Previous owners used wire longer than necessary and then just bundled it up to shorten the slack, so while it looks like many wires, its just 2. one going in, and one going out. (Edit: by going in and out I mean attached to the lower tab and the clamp using wire terminals, the cylinder doesnt have any actual wires itself)

    EDIT, thats a good thought , I had only checked voltage. I havent checked resistance yet. Ill check for varying resistance next.

    On one side of the tube, there are tightly spaced grooves all up and down the length of the tube ( you can see them in the first picture ), looks like so you could put clamps on and they wouldnt slide up and down as easy due to the introduced friction (EDIT, this is what I think you were talking about now that its sinking in a bit more).

    It reminded me a little of the old AFX controllers for the electric race tracks we had as kids so that prompted me to check voltage all up and down the length of the tube where it didnt change voltage (except for the unconnected tab), but I could see where maybe it might have to variance in the resistance somehow.
    Last edited by Robb; 03-29-2017 at 12:15 PM.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  5. #5
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    bobchase is on to something,

    found this picture of a variable resistor on google

    Name:  variable_resistor.jpg
Views: 190
Size:  59.4 KB

    The outside of the one I have conducts electricity all up and down the length, maybe it was wrapped at one time or I didnt test it like I remembered?

    Sure looks like thats what it is though.
    Last edited by Robb; 03-29-2017 at 12:16 PM.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

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    Re: Identify that mystery part - electrical doo-dad on Jeep

    Now you just need 25kV and your well on the way to making pictures fly through the air!

    The thing I wonder about is that you said that this is between the alt and the amp meter. Hooked up like you say, it would act as a limiting resistor. The only 'limiting' resistors I can recall for older vehicles were for the coil and the blower motor's speed control. The big white block that is attached to the firewall in the third picture is for the coil, so I have no idea why that resistor is there unless there is no regulator for the alt. I may be preaching to the choir here, but a three wire alt has an output, a ground, and an input. The voltage/current on the input terminal sets the output voltage, which typically is around 14.8-ish after a start-up and throttles back down to 13.8 ~ 14.2 depending on the outside temp and the age of the battery.
    Last edited by bobchase; 03-29-2017 at 12:53 PM.

  7. #7
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    Quote Originally Posted by bobchase View Post
    Now you just need 25kV and your well on the way to making pictures fly through the air!
    Ohh... so what youre saying then, is that its a tool of the devil ? just my luck. haha.


    So after refreshing memory on how stuff works, it seems like basically this old high power variable resistor is trying to function like a voltage regulator would, on a normal vehicle.

    I need to then look at the alternator, see if its internally regulated (but maybe not hooked up) or introduce an external voltage regulator appropriate to the alternator currently used.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  8. #8
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    Bobchase:

    Yep that white ballast resistor is for the ignition coil, I picked up an internally resisted coil so that I can ditch that from the engine compartment.

    There are 3 wires and then a ground on this particular alternator

    theres the black ground that goes from the body of the alternator and is just run over to where the battery is ground to the engine block,
    theres the yellow BATT cable that leaves the post of the alternator and goes to the variable resistor, and then to the ammeter
    theres the white wire thats on a molex connector at the alternator that then goes to the ignition switch (im pretty sure)
    theres the red wire thats on the same molex as the white wire and either its just taped up out of the way, OR its spliced into the yellow BATT cable. (Im not sure yet)

    if the red wire is just taped out of the way, that should be the voltage sensing wire and would explain why, maybe, the alternator is at full output and not regulating.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  9. #9
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    So going thru some more info...


    As it sits now, the way its wired, its simply a resistor. And as I discovered, its not changing the voltage.

    Does it make any sense in having a resistor in the charging system, maybe to keep things from shorting-out further down the line maybe, in case a bare wire hits metal ? Would that keep a wire fire from happening, for instance ? Or is that still a risk that would occur just from having the battery connected.


    In order to actually reduce the voltage, the unconnected terminal towards the top of the cylinder, should actually be grounded .
    Grounding it would turn it into a voltage divider / potentiometer and that would allow me to do a voltage drop which if there isnt a functioning voltage regulator, I guess that could kinda work even though I would think it would be a little rougher on the alternator.

    https://www.youtube.com/watch?v=GvEQiNF35c4
    Last edited by Robb; 03-29-2017 at 05:46 PM.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  10. #10
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    Could it be something of a RF filter? My CJ had a good sized one, but did not look like that.
    Get Down With the Sickness!

  11. #11
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    OK I think I now have this situation figured out.

    Looked up some data on old tractors.

    The reason to put a resistor in-line with the alternator output is to trick the alternator into seeing a load and to engage (charge) at lower RPMs. If its sits idling much, this is valuable. So Ill just go with that but Ill verify the resistance its set at. Looks like a good reason to leave it in place, but cover it up.

    The voltage problem Im seeing is either the red sense wire from the alternator NOT being connected at all, or: I have a bad voltage regulator inside the alternator.

    The area around the battery appears to have had a catastrophic battery failure in the recent past so its quite possible that the alternator overcharging had fried out a battery before and it didnt get fixed, just a new battery.


    Thanks guys for helping me work this thru, Ill follow up later with a result.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  12. #12
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    hey Bugs !. There is a part called a "filterette" that is a box that mounts under the dash, it was meant to reduce RF so that the vehicles wouldnt interfere with radio equipment and stuff like that, but its not integral to the operation of the vehicle. Not sure how exactly it wires in to the system though, yet. I dont have one.

    ---

    OK I think I now have this situation figured out.

    Looked up some data on old tractors.

    The reason to put a resistor in-line with the alternator output is to trick the alternator into seeing a load and to engage (charge) at lower RPMs. If its sits idling much, this is valuable. So Ill just go with that but Ill verify the resistance its set at. Looks like a good reason to leave it in place, but cover it up.

    The voltage problem Im seeing is either the red sense wire from the alternator NOT being connected at all, or: I have a bad voltage regulator inside the alternator.

    The area around the battery appears to have had a catastrophic battery failure in the recent past so its quite possible that the alternator overcharging had fried out a battery before and it didnt get fixed, just a new battery.


    Thanks guys for helping me work this thru, Ill follow up later with a result.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  13. #13
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    The wiring mystery has shifted... but less of a mystery now.

    Apparently Im becoming mildly color blind or just cant remember stuff like I used to. I had the wiring wrong in my head.









    I unbundled the bunch of wires and the alternator output is NOT going through the resistor. The white wire of the alternator that goes to the ignition switch was looped in through the resistor , and then the sense wire was also tapped into that white wire too. Well that did not make sense at all.

    I ended up re-routing the red sense wire over to the alternator output like is commonly done in a 12v conversion, ( I left the resistor in place with the ignition switch thinking maybe it keeps feedback from occurring that might otherwise keep the engine running if the switch is turned to "off" , a light is often used here I guess ?) and fired it up and it started faster than usual and ran great. But then the volts kept creeping up into the 16 volt range, so I went ahead and pulled the alternator and Ill take it to the city with me and have it checked/get a new alternator. The voltage regulator is still suspect for being bad.

    Also I was able to do some testing and the variable resistor is a 50 ohm model and its positioned so as to be a 12.5 ohm resistance on the slider.

    Once I get the alternator and voltage regulator thing straightened out, I can then go thru and start cleaning up the wiring, a lot of it is solid-core wire instead of multi strand , guess thats all the guy had available when he did it.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

  14. #14
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    Hey Robb, I'm sure you already know this but that alternator is about the simplest setup you can get. Obviously the threaded terminal is the output of the alternator. Of the 2 other terminals, one is used as a "sense" wire, this should go directly to the battery. The other one simply needs voltage when the ignition is on. The voltage regulator is internal to the alternator and there are only 2 things that would cause it to overcharge, either the "sense" line isn't connected properly or the internal voltage regulator isn't working properly. That should narrow down what's going on.

    I was thinking about the gigantic resistor under there too and I was curious if this Jeep used to have a 6 volt electrical system. If it did, they previous owner may have used the resistor to drop the voltage to the 6 volt components in the system, may be something worth looking into.

    It looks like a fun a project, let us know how it goes!
    I'ma cookin' somethin' up!

  15. #15
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    Re: Identify that mystery part - electrical doo-dad on Jeep

    Hey Jim,

    Youre right its not near as complicated as my first glances had it. That resistor spooked me and it turns out the way it was being used it didn't have be a high power one at all. Total overkill. That variable resistor was able to be wired as a potentiometer and could be used for voltage dropping. It wasnt, but it could have been.

    Made some progress. Have found tractor wiring diagrams to be more relevant to visualize what's going on in this old Willys. So that's been a big plus.

    Since there is no idiot light (which acts as a resistor), the variable resistor was added in when they did the 12v conversion. I considered just putting a red bulb tucked under the dash as a reminder if I left ignition in run. That would let me get rid of the variable resistor. Decided instead to just get a more modern 1-wire alternator then I won't need either the resistor, the bulb, or even that white wire anymore going to ignition key.

    The only thing left on there that's 6 volt now is the gas gauge and tank sender which they simply just cut the wires to and were just sure to always keep it topped off. Ive got a volt-a-drop and circuit breaker coming so I can hook that up again. All the lights were just a matter of putting in 12v bulbs. I just have 1 bulb type (fender blackout ) that's a bear to find in 12v , so I got volt-a-drop for it too.

    I was making all this too complicated, one of the previous owners was a whiz at Motorola in the 60's and 70's or whenever so I was nervous there might have been some old-tech rocket surgery going on. There really isn't though now that I've worked thru it all.

    Parts are on the way.

    I'm looking at moving the 12v starter solenoid off the firewall and over to where the resistor was sitting on the fender and putting that solenoid inside an old 6v voltage regulator case that's about the size of a thick cigar box, that would have originally been in that fender space.

    It'll look closer to factory that way, I'm figuring, plus I can get the original air cleaner back in there again.
    '14 Toyota FJ Cruiser, Off Road Edition
    '43 Willys MB
    LOWTECH 3-10-2007

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