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  • th400 downshift switch wiring?

    I want to rehook up the downshift switch, or passing gear switch, on the Caprice's TH400. It's basically a push button switch that is activated by the carb linkage opening to full throttle.

    There are two wires that connect to the trans. An orange and a black, I think. The plug and switch have four terminals, but for the life of me I can't figure out where the other two wires are, if there are any. And, which of the terminals the two wires from the trans go. The wires came out of the terminal connector and I don't know how where they go.

    Here's a pic of the switch with it's terminal markers. With the button out, the SW post and REL post are connected. With the button push in the IGN and SOL posts are connected.
    BS'er formally known as Rebeldryver

    Resident Instigator

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  • #2

    Re: th400 downshift switch wiring?

    Re: th400 downshift switch wiring?

    why do you have a switch for an overdrive 3 speed trans? You need a TH400 kickdown switch...they only have two terminals

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    • #3

      Re: th400 downshift switch wiring?

      Re: th400 downshift switch wiring?

      All of the TH400 kickdown switches I have seen (and I may have one somewhere) mount under the dash on the accel. pedal/firewall. One wire (12v+) to the spade on the driver side of the trans.

      Let me dig around in the attic and see if I can find it.
      Whiskey for my men ... and beer for their horses!

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      • #4

        Re: th400 downshift switch wiring?

        Re: th400 downshift switch wiring?

        The pedal mount switch thing started in 1971 in full size cars, I think....but look at your pedal bracket Scott and see if it has a place to mount a long sliding switch

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        "If it don't go, chrome it!" --Stroker McGurk

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        • #5

          Re: th400 downshift switch wiring?

          Re: th400 downshift switch wiring?

          It started earlier in Buick's I think but I'm familiar with that set up since it's on my '64 Nailhead. 2 wires, hot to the switch and then out down to a single blade terminal on the side of the transmission. Transmission grounds internally to fire the solenoid when you give it +12V. My switch is adjustable and bolts to the throttle lever on the carb.

          Central TEXAS Sleeper
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          • #6

            Re: th400 downshift switch wiring?

            Re: th400 downshift switch wiring?

            Buicks and Cads and some Olds mobiles thru 1967 had a 4 wire switch that also ran the switch pitch converter. The chevys all had a 2 terminal switch.

            My fabulous web page

            "If it don't go, chrome it!" --Stroker McGurk

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            • #7

              Re: th400 downshift switch wiring?

              Re: th400 downshift switch wiring?

              here's the 70s style pedal with the switch mounted on it, and the old 60s style carb switch, fits a Qjet






              My fabulous web page

              "If it don't go, chrome it!" --Stroker McGurk

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              • #8

                Re: th400 downshift switch wiring?

                Re: th400 downshift switch wiring?

                Here's some quick pics I took today to show you the setup on the car. No switch on the pedal. Two wires go to trans.

                I bent the bracket to get it to work with the Holley. I pulled the throttle back to show how it's supposed to work.


                No switches anywhere around the gas pedal.


                This is the driver's side of the trans.
                BS'er formally known as Rebeldryver

                Resident Instigator

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                • #9

                  Re: th400 downshift switch wiring?

                  Re: th400 downshift switch wiring?

                  A n.o.s. micro-switch that, mount to the pedal (in car) work great for this..

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                  • #10

                    Re: th400 downshift switch wiring?

                    Re: th400 downshift switch wiring?

                    The 1st one that Jim posted was the one I'm familiar with.

                    If you're running the DP, one of the N2O micro switches that mount on the carb would work just as good.
                    Whiskey for my men ... and beer for their horses!

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                    • #11

                      Re: th400 downshift switch wiring?

                      Re: th400 downshift switch wiring?

                      The 1st one that Jim posted was the one I'm familiar with.

                      If you're running the DP, one of the N2O micro switches that mount on the carb would work just as good.
                      That's a good idea. Does this car need anymore wiring? Or, does the switch in the trans work on it's own completing the circuit when the switch on the carb is closed?
                      BS'er formally known as Rebeldryver

                      Resident Instigator

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                      • #12

                        Re: th400 downshift switch wiring?

                        Re: th400 downshift switch wiring?

                        The switch needs power from the fuse block (switched power, only on when the ignition switch is on). The other side of the switch goes to the orange wire on the trans.

                        The last picture I posted shows the tab you bolt onto the throttle arm, that rubs against the switch plunger. The switch is designed to get kickdown before full throttle, that's why it has a longer travel than the switch you have. The switch you have is for a manual 3 speed trans with overdrive. It'll kind of work, but it's not right.

                        The microswitch idea is a good one, too.

                        My fabulous web page

                        "If it don't go, chrome it!" --Stroker McGurk

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                        • #13

                          Re: th400 downshift switch wiring?

                          Re: th400 downshift switch wiring?

                          Just adjust/bend tab on micro switch to kick it down a gear when you want it to. And now that I think about it, I have an extra switch and bracket laying on the bench if you want it. Its a home made bracket that bolts on the base plate in the two holes by the primary accel pump and hits on the accel pump arm. Let me know if you want some pics.
                          Whiskey for my men ... and beer for their horses!

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                          • #14

                            Re: th400 downshift switch wiring?

                            Re: th400 downshift switch wiring?

                            I found this article. But, it looks like the plug on the trans only has one wire. Mine has two.
                            http://www.highperformancepontiac.co...all/index.html


                            BS'er formally known as Rebeldryver

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                            • #15

                              Re: th400 downshift switch wiring?

                              Re: th400 downshift switch wiring?

                              I think B&M still produces those too.
                              Whiskey for my men ... and beer for their horses!

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