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  • Electrical wiring cotinuity test

    As the title states I'm trying to do a continuity test on the wires under my dash on my 59 bird with my multi-meter. Right now I have my engine compartment completely gutted including wiring so no power to interior. I hook my one probe to the heavy yellow wire terminal on the plug that comes into the car that should be the feed to the light switch. When I put the other probe into both brake light switch wires, which are not hooked up, I get a signal in both terminals. I know It should be hot all the time but I figure with them not being hooked up to the switch it would only be energized on one terminal until the switch was activated. Also I am in the process of installing a tilt column in my car so I have the wires to the column unplugged. With the probe connected to the heavy yellow terminal I am getting a signal in all the terminals for front and rear turn signal terminals again these wires are not hooked up to column. I am also getting a signal on the blue wire with the blue female end which should be coming from the flasher and goes to turn signal switch. I believe this should only be getting switched power from ignition switch. One thing I want to point out is that I have three schematics that I am using, the one that is on this site, the electrical assembly manual and the schematic from classic car wiring.The one from this site and from classic car wiring show feed to the brake light switch coming from the "a" terminal on the light switch. the electrical assembly manual shows feed coming from the battery terminal on the ignition switch. Anyways my question is I am a little confused why I am getting continuity to all these terminals. I assumed that from the incoming yellow terminal I would have continuity to the brake light wire terminal. The wire from the flasher would only have continuity if the ignition switch was turned on, and the terminals for the turn signal lights would only have continuity if they were hooked up to the wires to the turn signal switch in the column and the feed wire hooked to turn signal switch as well. Am I wrong with this assumption or am I missing something in my test?

  • #2
    I am not the best help as I am challenging myself with technical stuff myself but I did learned that although continuity is helpful and I use it a lot, it must also be checked with another device like a bulb tester (but with live power so you need to be sure of the condition of your wires) as sometimes, for instance, continuity might goes through a resistance like a bulb filament. So it can goes the same through other "items" on the network...
    Just my input and for sure it is best for you to wait for better mechanics to jump in there.

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    • #3
      Thank you Eric for taking the time to reply. I am basically trying to determine constant and switched power feeds going to my new column turn signal switch. As stated above a little confused to why I am getting signals on multiple wires. Hoping to get someone to chime in about my testing.

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      • #4
        If the main yellow wire (the wire that runs from the battery side of the solenoid to the light switch) is disconnected at both ends then there should not be power or continuity to any lights, turn signals, etc. including the brake lights. If you have power windows there's a yellow wire that goes to the window relay and circuit breaker. There are multiple yellow wires so I would verify with an ohmmeter that you are testing the correct one.

        John
        Last edited by jopizz; February 13th, 2020, 02:31 PM.
        John Pizzi - Squarebirds Administrator

        Thunderbird Registry #36223
        jopizz@squarebirds.org 856-779-9695

        https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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        • #5
          Thanks John for replying, as I stated above no electrical wiring in engine bay or window relay. I am doing continuity test from the plug coming out of the firewall that hooks to the harness in the engine bay, it has 4 male pins and 2 female sockets on the plug. The one pin that has a heavy yellow wire is where I am connecting to and testing from there to wires that go to the turn signal harness which are unplugged from the column. At first I set my ohm meter to sound when connecting to end of wires and was getting a signal for continuity on the wires mentioned in my first post. After reading your commit I set my meter so I could see the readings. Hooked to heavy yellow terminal probed each wire that go to brake light switch (which are disconnected) I get .3 on one and 9.5 on other. Double green wire with green connector that goes to turn signal switch, assume this wire tied to brake light switch wire reading 9.5. If I put the 2 brake light switch wires together reading at this wire .3. Tested from heavy yellow wire to other wires that go to turn signal switch, readings are rt.rear turn 8.4, lt. rear turn 8.1, rt. front park/turn 12.7, lt. front park/turn 13.0 and last tested the blue wire with blue connector, which I assume is coming from the turn signal flasher with key off reading is 40.5 and with key on reading is14.6 which I believe is keyed power. I am surprised I am getting readings on turn signal wires being that they are not hooked up to column yet. Sorry for the lengthy explanation, again thanks for replying.

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          • #6
            Greg,

            The main yellow wire has no connectivity until it connects to the battery terminal of the headlight switch. If you are getting a reading then that yellow wire is terminated somewhere or you have a short in the plug. Do you have any wires on your headlight switch?

            John
            John Pizzi - Squarebirds Administrator

            Thunderbird Registry #36223
            jopizz@squarebirds.org 856-779-9695

            https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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            • #7
              John, Everything behind the dash is still wired up other than I disconnected the terminals that hook up to the steering column and there is no incoming power I am just testing for resistance to see what would have been normally constant hot and what would normally be key switch hot. Since I hooked up my multi meter to that incoming yellow wire setting the meter for ohms,I figured I could test resistance through headlight switch and the wires that normally would be hot would show low resistance on the meter ( brake switch wire, which it did) and the one that is key powered ( turn signal flasher wire, which showed high resistance with key off and low resistance with key on) which is what I expected. I was just puzzled as to the turn signal/ tail and parking lights terminals showing readings without all the wires hooked up to the col turn signal switch. Prior to me disassembling the car, everything worked fine when I had it on the road. Greg

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              • #8
                Greg, I'd like to go through your electrical concerns over the phone because this requires far too much typing. Call me at (248) 544-8834. If I don't pick up right away leave a message and I will return your call very soon. - Dave
                My latest project:
                CLICK HERE to see my custom hydraulic roller 390 FE build.

                "We've got to pause and ask ourselves: How much clean air do we need?"
                --Lee Iacocca

                From: Royal Oak, Michigan

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                • #9
                  The #18 green brake wire is getting it's power from the fuse on the head light switch which is fed directly from the #12 yellow wire.
                  It sounds like all of the other readings that are about 10 ohms are the brake light and turn signal bulbs.

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                  • #10
                    I just want to give a big thank you to Dave (simplyconnected), I was able to have a lengthy conversation with him in regards to my questions along with just an enjoyable conversation in general. Dave is a super guy with a wealth of information and is willing to help and share his knowledge with others. I would also like to extend my thanks to John (jopizz) for the time you take and knowledge you share with us, on this site, too. One other person is Ray (yellowrose) who helps us to find and connect to the right people or companies in our search for services or parts for our cars. I know personally that restoring our cars to original, it can be hard to find some parts, but if you are making modifications from original like I am, when you contact companies and tell them what you have they don't want to even talk to you. One last thing is that I would hope others, including myself, would continue to share their knowledge in the restoration and modifications that you are making on your cars. That will be the only way to keep this forum going.

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                    • #11
                      Oldcarnut, Thanks for your reply, you pretty much summed up what the readings I was getting on the terminals was from.

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                      • #12
                        Also check if the head light switch is in the on or off position, it will make changes in your readings.

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                        • #13
                          Greg thank you for your comments and yes we have some very talented people as members supporting our site. That is why I always say that square birds.org " is the best TBird site on the planet"
                          Dano Calgary,Alberta Canada
                          Thunderbird Registry
                          58HT #33317
                          60 HT (Sold )

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                          • #14
                            Greg, thank you very much for taking the time to comment on the assistance you receive from the leadership of this dynamic Forum! It is very much appreciated. When we lost our fantastic co-founders, and Webmaster in Alexander's case, Alexander Sosiak, (who also founded the Lincolns Of Distinction Forum) and Sandy Block, over 10 years ago now, we lost our founders and leadership. Thanks to Dan Leavens, then Dave Dare ~ simplyconnected, our webmaster now for many years, and John Pizzi ~ jopizz, and myself, we decided to step in and assume operation of the Forum to continue the legacy of Alexander and Sandy. We dedicate ourselves to the operation of the Forum of Alexander's, and built on it to now include all years of Tbirds, and even Big Fords and Trucks. As Dan has often said, it has become the best TBird site on the planet.

                            Ray Clark - Squarebirds Administrator
                            The Terminator..... VTCI #11178
                            Contact me via Private Message for my email address, or Call (Cell) 210-875-1411

                            https://www.squarebirds.org/picture_gallery/TechnicalResourceLibrary/trl.htm

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