TAC Tech => Electrical => Topic started by: Brewski on May 06, 2021, 01:34:54 PM
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I'm looking for a schematic or perhaps a description of how the shaker hood flap actuators are powered on my '72 TA. I have two actuators with one wire that attaches to the underside of the shaker. That wire joins the engine wiring harness behind the brake booster. Where it goes from there is a mystery to me. However, my shaker flap is not getting power. Not sure where to begin honestly. I'm guessing it might be tied to the kickdown switch by the gas pedal. Not sure what makes it open or what conditions are necessary for the actuators to become energized. I know the '74 GTO shaker used vacuum as a parameter. But I'm pretty sure the TA is strictly an electrical signal. My really cool laminated TA schematic doesn't show it. Any help or ideas would be appreciated. My apologies if this has been already covered. I did a search but came up empty.
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Welcome to TAC!
I've got the shop manual, but I've never looked at that. I'll see what I can find in there.
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The shaker flap was actuated by a carburetor mounted electrical switch.
Reproduction parts are available - https://www.firebirdcentral.com/1970_1971_Trans_Am_Functional_Hood_Scoop_Throttle_p/tra-2154.htm (https://www.firebirdcentral.com/1970_1971_Trans_Am_Functional_Hood_Scoop_Throttle_p/tra-2154.htm)
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If I understand the question correctly you don't know about the connection behind the booster. That's were the switch receives power through the fuse junction box. The carb switch just completes the circuit when the pedal is depressed and actuates the solenoid.
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Unfortunately, my carb does not have a switch. So the power and switching is coming from somewhere else.
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The 72 scoop control was different than the 70 and 71. The earlier ones had a carb mounted switch but the 72 used the automatic transmission kickdown switch to activate it. In automatic cars the switch needed to power three solenoids (2 in the scoop and one in the TH400) so it had a unique switch that could handle the current. My notes say it was PN 1235480 but that one-year-only switch isn’t reproduced (at least not that I’ve found). If you have a manual transmission it’ll also have a “kickdown switch” but it only activates the scoop so I’d guess the standard switch would likely work. As for wiring at the kickdown switch I’ve found no wiring diagrams that show it but it should be easy enough to ring out the wires near the gas pedal to find the one going to the scoop. Also, remember that the scoop needs to be grounded as it’s sitting on the gasket between it and the carb. I think the ground is another thing that is unique with the 72. In 70/71 there is a ground strap attached to the bottom of the scoop that connects to the firewall but the 72 uses a spring ground strap (identical to the spring that grounds the hood to the firewall right in front of the windshield antenna.) This spring is mounted to one of the top carburetor screws and contacts the metal bottom of the scoop.
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That makes sense. I have a 72 shop manual, and I don't see any wiring diagram for this system, but I was looking at the engine and maybe I should go back and look at the accelerator pedal. The power supply has to be shown somewhere. I did find an illustration in the "air cleaner" section, but it may be outdated based on Mace1971's comment. These illustrations are tiny but I was able to zoom in and get some legible info. I will include the whole thing here just for posterity.
(https://i.imgur.com/8xTKhwT.jpg)
(https://i.imgur.com/ZQaH1sg.jpg)
(https://i.imgur.com/3ZLulS2.jpg)
(https://i.imgur.com/KwXBZco.jpg)
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Did not know that, thanks for the clarification.
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I looked again at the wiring diagram, and it's not there. I did find the kickdown switch and that is wired through the bulkhead connector to the transmission. There's no optional branches shown that are really clear. The drawing's a little hard to read, so I might be proved wrong on that. The transmissions that year had two wires going to them. I was thinking this was switch pitch, but now I think it may have been transmission controlled spark.
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This question got me to looking for the source I had found years ago which described the 72 scoop control. It’s by Rocky Rotella. He explains the the updated system for the 72 wasn’t documented in the shop manual or even a change notice. https://www.hotrod.com/articles/0407pon-pontiac-shaker-hood-scoops/
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P120-121 of 1972 Assembly Manual for similar but possibly clearer version of shop manual above.