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Bad Power Antenna Ground

Discussion in '308/328' started by jsumnertx, Nov 15, 2020.

  1. jsumnertx

    jsumnertx Karting
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    Dec 9, 2004
    122
    Austin
    Sometime in the first 18 years of my car's life, the power antenna was replaced with an ugly whip antenna. Since the only sound-system I've used in the past 20 years is the engine, it hasn't been a priority to fix. But it is ugly and I've gotten sick of it - so I've been following the various threads for switching back to a modern antenna. It looks like the wiring harness at the antenna has a bad ground. Wasted a ton of debugging time getting to this point - lesson learned - check the grounds immediately.

    Since it's never worked, I'm a little suspicious of the way the ground strap is wired. Can anyone confirm this is the proper place for the antenna ground to be attached to the "chassis"? Mine is just going to a hole in the luggage compartment.

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    See the yellow circled area. The ground strap goes to that screw and the screw just goes into a hole in the bulkhead there. The whole area is covered with carpet adhesive. Seems like it makes almost no contact and I can't imagine how this is making a good connection with anything. The resistance between that screw and a place that I know is grounded, like the trunk latch - is infinite so no connection at all.

    If this is indeed the right place, is the ground the metal backing? I could get out mineral spirits and try and strip away that adhesive gunk. Another possibility is that there is some wiring behind that bulkhead. I recall something behind the wheel well cover in that area that seemed to be poorly connected or disconnected last time I took that area apart. But if someone knows, I'd love the pointers.

    Oh, BTW, in the process of debugging, I found that the power antenna switch has two blades that are internally connected. One blade goes to the 12V side coming from the fuse. The second blade is not connected to anything. Since the battery provides 12V at all times to this blade, the other blade is energized with no cover or anything - just a bare wire providing a handy 12V to anything that comes in contact during vibration or anything. Nice... I capped it to give it at least a little protection for the future.

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  3. Steve Magnusson

    Steve Magnusson F1 World Champ
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    #2 Steve Magnusson, Nov 15, 2020
    Last edited: Nov 15, 2020
    The unusual answer is: "there isn't a ground connection". On the stock '78-'79 system, using the stock aerial motor, only the two BR (white-red) wires go to the antenna motor. Push the stock antenna switch one way = one BR wire is +12V and the other BR wire is ground = runs the motor one direction. Push the stock antenna switch the other way and the voltages are reversed and the motor runs the other direction.

    An aftermarket antenna motor might have three wires, or two wires and the body is ground, where you put +12V on wire #1, nothing on the wire #2, and wire #3, or the body, is ground = runs the motor one direction. Put nothing on wire #1, +12V on wire #2, and wire #3, or the body, is ground = runs the motor the other direction.

    The stock switch only works with the stock-style antenna motor (where reversing the polarity reverses the motor direction). If you want to use a 3-connection aftermarket antenna motor (where which wire getting +12V determines which way the motor runs and has a constant ground connection), people have posted clever solutions using a DPDT relay (and an added ground) to make the stock switch work with it. If you can't find those threads (and want to use a 3-connection aftermarket antenna motor) give a shout, and I can dig it out.
     
  4. jsumnertx

    jsumnertx Karting
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    Dec 9, 2004
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    Austin
    Interesting. Ok, I could see that wiring arrangement. It seems to be different than the wiring diagram I’m looking at and the way the car may be wired - but of course it’s never worked so that could be a thing. Can you help me decode a few things?


    1) this picture is from the online user manual I downloaded. It shows that the switch provides +12 to one wire or the other and that the antenna motor is grounded. Are you saying this version of the manual is different than my car?

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    2) my switch is definitely wired like the diagram above and seems to behave like that diagram. When I put a voltmeter across the two terminals with the striped wires, you get basically no voltage. But if you go from one terminal to ground, it will give you 12V when the switch is just that direction. I don’t seem to get a voltage between the two Here’s: the switch

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    is both the wiring diagram and the switch wrong?

    3) if both are wrong, do you know the part number and how the switch should be wired?
     
  5. Steve Magnusson

    Steve Magnusson F1 World Champ
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    My bad -- I should've looked at things rather than just typing from memory. I have it backwards for aftermarket vs stock (aftermarket is the one that swaps polarity) -- so you should have a ground connection somewhere (but can't help you with that).
     
  6. kiwiokie

    kiwiokie Formula 3

    Aug 19, 2013
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    On my GT4 the ground is a metal strap that supports the base of the unit and the other end is bolted to the steel in wheel arch.


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  8. jsumnertx

    jsumnertx Karting
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    Hey Steve. Thanks for the update. I now see there seem to be a couple of styles, even for Ferrari. Birdman references his 77 being a DPDT that reverses 12V/GND. Seems this area evolved over time. Hopefully the wiring diagram I have is correct for my model year and I'll keep digging around in the wheel well for where that sucker is supposed to get real ground.
     
  9. thorn

    thorn F1 Rookie
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    My QV antenna is driven up/down by the stereo (not the toggle), but the activation theory is the same.

    There are 2 wires to the antenna, both red-striped. Polarity switches up and down. There is also a ground wire (more like a strap), which connects to the body in the trunk area. It's in the same area as the one in your image, but my car doesn't have all the glue/gunk that I see in your image.
     
  10. jsumnertx

    jsumnertx Karting
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    Dec 9, 2004
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    After pulling the wheel well arch, I can see the screw goes through and runs into nothing but rustproofing. No frame in sight. Screw location must have been moved at some point 1979-1997, maybe when the car was turned resale red in the 80s

    #thatsnotground (barely see it where the yellow circle is). Next step to find a new location that hits a frame piece.

    (side observation - does the wiring chart give a sense of wiring harness bundles? Next mystery is what that unconnected connector is)



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  11. Steve Magnusson

    Steve Magnusson F1 World Champ
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    At the risk of being wrong twice in one thread, I believe that that's the connector for the suction fan motor that evacuates the gas fumes from the airbox to the charcoal canister at engine shutoff (one pink wire and one black wire):

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    Has your suction fan motor been removed?
     
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  13. jsumnertx

    jsumnertx Karting
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    Bingo. Mine had been removed at some time in the past. My canister is not connected and that unit is missing from those bolt locations. Thanks!
     
  14. TurtleFarmer

    TurtleFarmer Karting

    Jan 13, 2020
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    @jsumnertx Well, I think your ground strap is definitely stock. Or, alternatively, both our cars were owned at some point by the same crappy PO who felt a braided ground strap to a sheet metal screw on the fender well surrounded by gunk was a good idea.

    Here's the same area in my '79 GTS
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  15. TurtleFarmer

    TurtleFarmer Karting

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    Oh...and I forgot to ohm it out...I can do that in the morning.
     
  16. jsumnertx

    jsumnertx Karting
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    yeah please. Best ground I found in the trunk was the deck lid latch. Straight ground to the cam covers. I ended up finding a metal plate in the engine bay and ran the ground to that plate. Antenna is going up consistently and only inconsistently and partially down. Now on to that problem.
     
  17. TurtleFarmer

    TurtleFarmer Karting

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    Will put a meter on it in the morning and send out.

    Also, took a quick grab from a '78 OM wiring diagram: good confirmation that there was indeed a crappy little ground strap coming off the antenna motor (81) going to a local ground in addition to the two power lines coming from the switch (BR - white/red)

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  18. kiwiokie

    kiwiokie Formula 3

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    WD40 works great at cleaning up the surface of the aerial so the sections slide over each other easier.


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  19. jsumnertx

    jsumnertx Karting
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    Wow. Yours does look exactly like mine. Now I'm even more confused.
     
  20. TurtleFarmer

    TurtleFarmer Karting

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    Just put a meter on it...it's not a good ground (same as yours). I'd have to remove the fender liner to figure out what that fastener is screwed into, but I'd hazard that the problem is the fastener itself and not the stick or body panel that it's attached to. A magnet near the fastener area indicate there's metal in there somewhere.

    Of course that lower body panel (part #60329802) that starts six inches below the ground strap is fiberglass with embedded metal bosses (for attaching the fender liner), so my magnet check near the ground fastener may only be indicating a floating piece of metal. However, I'm sure that no one would have put a ground strap to a floating piece of metal.

    It would be kinda ridiculous, but it's possible that the ground was expected to be pulled thru the threads of the fastener rather than the head--which would be seriously awful electrical design, but perhaps that's what's happening here. In that case, oxidation (rust) on those threads could make it crazy difficult to create a decent ground path.

    I don't currently have an antenna but it's on my list to add one and I'm planning to try to preserve the motor functionality. Very curious to hear what you find.
     
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  21. Imatk

    Imatk Karting

    May 6, 2007
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    Interesting that you're doing this. I just got my aerial to go up but it won't go down. Not sure if it's the switch or motor at this point.
     
  22. jsumnertx

    jsumnertx Karting
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    Dec 9, 2004
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    Austin
    I think it's now done enough. Thank you @kiwiokie for the WD40 suggestion - that seemed to be the last piece

    Summary:
    Rather than fix the original spot, I moved the ground connection to be in the wheel well. Buttoned everything else up, had the struggle with it not going down all the way, and ended up with WD-40 as being the fix.

    Ground fix:
    I found a spot in the engine compartment where one of the accessories used to be, filed off some paint at that area to get a good contact, and attached the ground strap with the strap on one side and the nut on the other with a lock washer. Got good ground there. Ran the strap as far as I could and made an extension with some wire, ran it back into the trunk using the hole for the antenna coax, and put connectors on either side. Got a good connection.
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    Debugging tips for posterity:
    * Removed the antenna and made some pigtail extensions. Tried the antenna connected straight to the battery. Good way to test if it's the antenna or something between the antenna and the battery. It went up just fine and down just fine.
    * Found a chassis ground and repeated the experiment with the antenna to chassis ground and the antenna input straight to the battery. Still went up and down just fine.
    * Those pigtail extensions allowed me to clip on a multimeter. Plugged the antenna back in to all of the connections in the trunk and had the red multimeter lead on 1 12V antenna input and the other on the ground strap, meter on DC volts. If the antenna was going up smoothly, the voltage was around 12.0 (car off, battery only). If the antenna was going down and got "stuck", I still got 12.5V on the meter. Told me the switch was fine.
    * If you're suspecting switch problems, you can reverse the two leads where the antenna goes into the harness in the trunk and see if it now has problems in the reverse direction. I had done that step earlier and found it still got stuck going down and was fine going up.
    * If you really want to get to the switch, you can try and remove it and reverse the leads at the switch. I'm not sure this tells you anything new though compared to reversing it at the trunk.
    * After getting good voltage at the antenna itself, then I tried WD-40 and that made things much better.
    * If that hadn't worked, I was going to try and get a current reading on the multimeter and see if some current limiter was getting tripped on the way down.

    Note, I find if I put the antenna up partway and then immediately down, it does tend to get stuck more. If I go all the way up and, wait a sec until it's clearly been up for a second or two, and then put it down, it seems to consistently go all the way down. Not sure if it's the design of the antenna or what

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    My pigtails for debugging. Good spots for the multimeter to clip on to
     
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