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Another Horn Question-74 Cj5

Discussion in 'Intermediate CJ-5/6/7/8' started by BellhreyFarm, Apr 22, 2021.

  1. Apr 22, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    After troubleshooting my horn I’ve come to realize I don’t have constant 12v, but instead I get 12v when pushing the horn button. So basically the opposite of what I need. My wiring seems to be ‘original’ with a red(+) and black with yellow tracer. Can anyone point me in the right direction? Thanks!
     
  2. Apr 22, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    If you look at the wiring diagram, it's straightforward. Power comes from the solenoid (C12-A12) to a splice under the dash, where it travels to the horn (A25-B25). It then travels back to the dash (B27-A27) and to the horn button in the column. At that point it is grounded by the horn button and the horn sounds.

    https://oljeep.com/gw/74_tsm/22-7-CJWiringDiagram.pdf

    The colors are in a legend separate from the diagram. Identify by circuit number.
    https://oljeep.com/gw/74_tsm/22-WiringDiagrams.pdf

    Maybe you are confused by a voltage measurement along the way? At any point between the wiring and ground, you will see full battery voltage (12V). All the wiring referenced above is floating at 12V. Your meter has a huge input impedance compared to the circuit, and any measurement along the way will only need a tiny current for the meter. This will not detectibly affect the circuit. Once you ground the button, significant current will flow and the horn will sound.

    If your Jeep is not wired like the factory diagram, it's up to you to figure it out. Trace it with your meter, draw it out on a big sheet of paper. Without the Jeep in front of you, diagnosis will be effectively impossible.
     
    Last edited: Apr 22, 2021
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  3. Apr 22, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    You know how sometimes you have to ask someone where something is and immediately you remember where you put it?!? Ya, went back through the wires, reattached new Wolo 370 horn from Walck’s and boom I have a working horn. Yay!! Thanks timgr for the quick response and the TSM. I’ve used it multiple times already. Call me crazy, but I’m having a blast troubleshooting. Luckily, majority of electrical works and everything that I’ve seen so far is original so easy to track. Now on to the fuel and temp gauges! Ha! I’ve already read John Strenk’s Troubleshooting guide. My only question is do I need to unhook battery when testing ohms on gauges/sending units? I’m paranoid I’m going to smoke my qauges.
     
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  4. Apr 22, 2021
    John Strenk

    John Strenk Member

    Shalersville, Ohio
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    That would be the safest but just having the power turned off with the key is enough. Beside, It's best to disconnect all the wires when doing an ohms test.
    Make sure you have a good grounds. That will keep the magic smoke where is belongs.

    I'll have to look up if the 74 had an external regulator for the gauges. If it does, then the resistance test will be a little different.
     
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  5. Apr 22, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    Thanks for your response! From what I’ve seen my speedometer is not original to a 1974 cj5, will that change whether or not I have an internal or external regulator for the gauges? Currently the speedometer works, but neither gauge(fuel and temp) or odometer shows any life. And the amp light stays on when engine is running. So I have my work cut out for me! 75E0DFAD-6DE7-410C-919B-689370575B2D.jpeg
     
  6. Apr 24, 2021
    John Strenk

    John Strenk Member

    Shalersville, Ohio
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  7. Apr 24, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    Yep, mine has 3 posts.
     
  8. Apr 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    There is a lot on the internet written about this. Most Wagoneers and J-trucks have the same configuration, except the CVR (constant voltage regulator) is in the temperature gauge instead of the fuel gauge, and unlike the CJ it also powers the oil pressure gauge.

    I don't know why they named this a "constant" voltage regulator. It's actually a PWM (pulse width modulated) regulator that turns on and off about once a second. The average voltage over time is something around 5V, but the instantaneous voltage is either 0 (off) or battery voltage (on). Anything but constant.

    On the CJ, the CVR needs three connections - battery voltage in, regulated voltage out, and GROUND through the gauge case to the cluster to the dash. The gauge actually has 4 connections, with an additional connection to the fuel level sender. Don't try to operate the gauges without a ground to the cluster. The default state for the CVR is on, and it won't cycle without a ground. A constant 12V to your gauges will burn them out.

    You can replace the internal CVR with an external IC (integrated circuit) called the 7805 voltage regulator. Unlike the CVR, the 7805 delivers a constant 5V from whatever the battery voltage is (more stable). The gauges will also respond faster with an actual constant input voltage. The 7805 will turn off if it loses ground, which is safer for your gauges. If you have a defective CVR, you can replace it with the 7805 and keep the original gauges. (If you want to replace the CVR, you'll have to replace it with a complete aftermarket gauge of dubious quality.) Excellent upgrade even if your gauges work fine.
     
    Last edited: Apr 24, 2021
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  9. Apr 24, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    As always, appreciate the knowledge. I’m getting a good 12v to the fuel gauge, but definitely not getting 5v on the ‘A’ post. It’s closer to .5-1.0v. So I’m chalking it up to bad regulator. I would like to keep original gauges so thanks for the info on the 7805.
     
  10. Apr 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Done this on my J20 and it works great.
     
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  11. Apr 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    It should be cycling on and off. NB your multimeter (esp a cheap one) takes a while to convert each measurement, and may get confused by the PWM signal. A test light would be better.

    Be sure to post up if you have questions.
     
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  12. Apr 24, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    I have a Fluke 179. It’s cycling, but not getting anywhere near 5v.
     
  13. Apr 24, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    Do you happen to have a picture of your install?
     
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  14. Apr 24, 2021
    John Strenk

    John Strenk Member

    Shalersville, Ohio
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    I think the reason it was called a 5 volt regulator was because the instrumentation (VOMs) at the time had a very slow response time. I hooked up my old Simpson 520 and it read around 5 volts with a little fluctuation.
    That is probably all the mechanics could measure at the time.

    With a Modern DVM, Try putting it on a higher range if it has that capability. That slows down the response time or maybe just averages out a number of readings.

    But DVM's can be misleading, I prefer a test light also. It should flash about once per second if the regulator is working properly.

    I also experimented with a 'Ghetto Gauge Fix" https://www.jeepforum.com/forum/f8/ghetto-gauge-fix-4424051/

    It's cheap ($9.00), easy to connect even if you don't know anything about electronics and completely waterproof so those of us with leaky jeeps don't have to worry about getting water on anything and shorting out.

    [​IMG]

    Our OEM gauges polarity insensitive. They work either Positive or Negative ground and automatically adjust for temperature changes to remain 'accurate' .
    With a solid state regulator, you loose that self regulation because the regulator and the needle movement are both done by a bimetallic strip that is effected by ambient temperature. So as the temp goes up the regulator gives slower pulse rate compensating for the extra heat.

    With a solid state regulator, if the ambient temperature is Low then the Temp and Gas gauge will read low and if the ambient temperature goes up high, the gauges will read too high.
     
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  15. Apr 24, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    This is great info, thank you! I have another dvm that allows me to extend my range and it definitely gave me numbers closer to 5v. But still all over the place between 3-8v. I also found my test light and it did exactly what you said and flashed slightly faster than every second. Would you consider this a working regulator and move on?
     
  16. Apr 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Mmm, not to contradict John Strenk - he has posted a lot of good and useful upgrades before - but I think he's off track in this reply.

    A 7805 is 43c at Mouser electronics. Add two 25v 0.1uf capacitors at say 10c each for a total cost of 63c, plus shipping. Add some scrap wire, heat shrink and a few connectors - no different from his solution.

    A 7805 from ON Semi has something like a -40-125C temprature range. Specified temperature drift is -0.8mV/1C or -0.132 volts over the entire range. This is not going to affect your gauges, which are advisory at best. Others have used a 7806 at a 6V fixed voltage and seen no difference in gauge performance. I can't imagine that the factory performance range in response to temperature is better than this. After all, it's a bimetallic strip that opens and closes, and that will clearly be affected by the ambient temperature.

    Here's a thread with similar coverage: Instrument cluster voltage regulator upgrade - Full Size Jeep Network I didn't take any pictures because I felt this topic had already been done to death. The FSJs are a little different from CJs, but all you have to do is disconnect the 12V input to your CVR and connect the 5V output from your chip to the CVR output of the gauge. Not difficult or expensive.
     
    Last edited: Apr 24, 2021
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  17. Apr 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Yeah, I would think so. My next step would be to test the sender. You can substitute fixed resistors for the sender and test the gauges, then test the senders with your meter. I built a gauge tester here Build A Gauge Tester which I subsequently gave away. You don't have to build a fancy tester - some clip leads and fixed resistors work just as well.
     
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  18. Apr 24, 2021
    BellhreyFarm

    BellhreyFarm ‘74 CJ5- Should’ve bought one sooner…

    Cameron, NC
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    Great job on the gauge tester! The article won’t let me open the pics/attachments though. I’ll probably stick with clip leads and fixed resistors for now. Maybe that can be a winter project!
     
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  19. Apr 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Thanks on the tester.

    I'm not hosting the pictures. They were all uploaded to the site. Suggest you ask the mods (Focker sp) what's up.
     
  20. Apr 24, 2021
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

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    Second thought - you could post in the help forum above.
     
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