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Thread: shift light

  1. #1

    Default shift light

    my shift light on my 85 gt dosent work any ideas ? when the key is turned on it dosent light up but if i put a test light on it its getting power is the bulb the same as the others thanks

  2. #2

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    Not 100% sure, but I don't think the stock shift light functions on the 5.0 cars. I know it doesn't on my 86 GT. I had an 85 4 cyl stick shift mustang that it did work in.
    Andy G.
    1986 Mustang GT vert, 2R, original owner, 5 spd, 19k miles
    1986 Mustang SVO, 1C, comp prep, 3rd owner, 48k miles
    1989 Ranger GT -SOLD-
    2004 T-Bird, triple black, SST

  3. #3

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    wow anybody else hear of this

  4. #4
    FEP Senior Member svo6's Avatar
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    The light on my 86 has not worked since the day it was new! Dont think they were suppsed to.
    408 C.I.-Sleeper

  5. #5
    FEP Super Member Bryan Knebworth's Avatar
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    Default

    My '83 GT has the light, and the original owner told me his disconnected it since it was "annoying" lol

  6. #6
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    qikgts's Avatar
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    Default

    Mine works when the engine gets warm enough... There's a thermal switch on the manifold which allows the circuit to become active and there is also a "module" right around the column that is part of it too...
    '85 GT

  7. #7

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    The light functions just fine on my '85 T-Top car.

    There is no "prove out" function for the shift light, like there is for some of the other warning
    indicators. And the light is not supposed to work when the engine is cold, or whenever the
    transmission is in 5th gear.

    The shift light needs tach pulses, a vacuum switch on the back of the driver side strut tower,
    a top gear inhibit switch, and the electrical connection on one of the thermal vacuum switches.
    If any of these are disconnected, or not working, the shift light won't ever illuminate.

    The shift light should have voltage on one side whenever the key is on. The ground for the
    light is provided by the upshift module, in response to the tach and vacuum switch inputs.
    The top gear inhibit switch, and PVS switch are in series with the connection from the light
    bulb to the module.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  8. #8

    Default

    I would say that Jeff nailed. Also as another data point, the stock shift light used to work in mr '85 GT when the car was mostly stock.




    --Vince
    + Jalapeņo Red 1985 Mustang GT, 347 in^3, Canfield heads, 650DP, X-Celerator, & 1-5/8" LT's
    + Tremec 3550, D&D shifter, 3.73:1 gears, & TrueTrac differential
    + EVM watts & 3-link, Homemade LCA's, & Koni SA's
    + '00 Cobra R Brembos in front and SN95 Cobra rear brakes, R58 rims, & 275/40R17 Falkens
    www.1985mustanggt.com

  9. #9

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    I think you can get the light socket from the link below. I found my socket missing during my 3G install.

    http://www.dormanproducts.com/p-23945-40245.aspx
    84 GT. Drop Eibach springs, KYB shocks W/quads and tube upper & lower control arms, short throw, Welded subframe connectors, cast camb plates, Mac shorty headers, 2.5 back with cats, underdrive pullies, Weiand intake, 600 holley, 8.8 W/373's. Ugly but fun.

    05 V6. Mama's pony. GT rims.

    04 Jeep Grand Cherokee

  10. #10

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    '86s don't have them. I know that '85s do, because I remember test driving one about 20 years ago, and it would come on around 2000 RPMs... anoyingly low, but it was probably for fuel economy purposes.
    Project "WinBacK" 1986 LX Hatchback
    - CA car, 5.0 w/5 speed
    - Cobra 17x8.5's + Modded Mach1 Chin Spoiler + 83-84 Hood & Scoop/85-86 "Blackout"+ FMS Mass Air Kit+ MM Clutch Cable & Quadrant + Fiore Cable Adjuster + MM SFC's+ Wild Rides "Battle Boxes" + Explorer Intake, Converted TB & Injectors, 70 mm Mass Air Meter + BBK Ceramic Shorties + 2.5" Bassani O/R X-Pipe & Cat-Back Exhaust w/ 3" Tips + 3L27 w/ Carbon Fiber Clutches​(out of retirement) + Pistol Grip Shifter + 99-04 GT Front/00 Cobra Rear Disc Brakes

  11. #11

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    The shift light comes on at a low RPM, if you're light on the throttle. If you have the throttle
    matted, it doesn't. The whole idea was to encourage you to upshift when you're just loafing
    along, to save fuel. I don't know, but I think the upshift light was one of the measures that
    helped Ford meet their fuel economy targets for '85, without using the Two-Speed Accessory
    Drive.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  12. #12

    Default

    ^^ That makes sense. ^^
    Project "WinBacK" 1986 LX Hatchback
    - CA car, 5.0 w/5 speed
    - Cobra 17x8.5's + Modded Mach1 Chin Spoiler + 83-84 Hood & Scoop/85-86 "Blackout"+ FMS Mass Air Kit+ MM Clutch Cable & Quadrant + Fiore Cable Adjuster + MM SFC's+ Wild Rides "Battle Boxes" + Explorer Intake, Converted TB & Injectors, 70 mm Mass Air Meter + BBK Ceramic Shorties + 2.5" Bassani O/R X-Pipe & Cat-Back Exhaust w/ 3" Tips + 3L27 w/ Carbon Fiber Clutches​(out of retirement) + Pistol Grip Shifter + 99-04 GT Front/00 Cobra Rear Disc Brakes

  13. #13
    FEP Senior Member smokinn85's Avatar
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    My light stopped working after I started heavy modifications to my engine (including stripping all the smog equipment). I'm not complaining because it was very annoying for me.
    85 GT, 331 Stroker, Forged crank/pistons, AFR185's, 1.6 rollers, CompCams blower cam (35-312-8 ), Performer RPM Intake, Summit Racing 600, MAC 1 3/4" Ceramic Shorties, Stainless 2 1/2" X-pipe, MAC Cat-back w/ 3" tail pipes, Poly bushings front 2 back, 10.5" clutch upgrade, WC T-5, Pro 5.0 Shifter, Tri-ax handle, Granitelli LCA's, BBK Specific Rates, 8.8 w/ 3.73's & Ground Pounder Girdle kit.
    http://www.youtube.com/watch?v=od4j41_xXQM
    http://www.youtube.com/watch?v=jSPrj...eature=related

  14. #14

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    I read somewhere that they started in 83, but have ever seen mine come on. I figured that maybe it was a running change along with the T5, because I have an SROD.
    Tony

  15. #15

    Default

    where is the top gear switcth located on the tranny? who sells them

  16. #16

    Default

    It's on the top cover. It's actually the same switch as the later ones with the neutral indicator
    switch, just screwed into a different hole, and I believe also the shift rail may be cut differently.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  17. #17

    Default

    do i have to drop the tranny to get to it

  18. #18

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    anyone?

  19. #19
    FEP Power Member 69SCJ's Avatar
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    Default

    If I remember correctly you can get to it without dropping the tranny. Again, if memory serves me, it is high on the driver side of the tranny. I bet Jeff knows for sure though.

    Mine works in my 85, but I pulled the bulb last year 'cause it was kinda annoying.
    Black, 85 GT, T-top, 5sp, ......SOLD WAH!!!
    68 F100, 4x4, 390, 4 sp.
    68 Bronco, Roller 302, injected, auto, being modded!
    2010 Raptor, SCAB, 6.2.......
    2012 Focus, little motor.

  20. #20

    Default

    I was just thinking about this last week.... wondering if anyone around here has done it before. Ist there a way to get an aftermarket shift light module and wire it up to use the factory shift light. I haven't really messed with shift lights before, so I'm not too familiar with how they work.

    My shift light doesn't work at all anymore, but it would be nice to add so functionality back using the old instrumentation

  21. #21

    Default

    mine has never worked in my 85 gt either.

  22. #22

    Default

    I'm new here. I have an 85 GT 5 speed and my shift light is intermittent. Sometimes it comes on and sometimes it doesn't. It seems to work when I hit a bump. I was told it could possibly be the shift indicator relay. Please help!!!

  23. #23

    Default

    The shift light does not use a relay, it's controlled by an electronic box. Your problem is more likely a
    wiring issue, either to the top gear switch on the transmission, or to the ported vacuum switch on the
    intake manifold, that has the electrical connector on it. The former is a normally closed switch that
    opens in 5th gear to inhibit the light. The latter is a normally open switch, that inhibits the light when
    the engine is not up to operating temperature. Both switches basically interrupt the power feed to the
    light.

    The third leg of the shift light is a vacuum switch on the back side of the driver's strut tower. On the
    '85s it shares a bracket with a switch that controls the TAD solenoid. If the switch leaks, or is not
    getting vacuum, it can indicate to the controller that you're at WOT when you're not.

    Or maybe the bulb itself has an intermittent connection, or a broken filament.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

  24. #24
    FEP Member Mgino757's Avatar
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    Jan 2011
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    Virginia Beach, VA
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    Default

    My light has worked before, but there isn't a vacuum switch behind my driver's side strut tower. My PVS on the intake manifold has gone bad though, the one with the electrical connector and red top. It doesn't switch over to ported vacuum when at operating temp. My job sells the ported vacuum switches, but only the green and blue ones. Anyone know what temperatures these blue and green switches operate at?
    Last edited by Mgino757; 05-15-2014 at 10:43 AM.
    1985 Mustang GT conv. modified 4180C, Weiand Street Warrior intake, equal length headers, true dual exhaust, 3.55:1 8.8'' rear end, 2003 V6 T5, Ford Racing 10.5" clutch.

    1998 Mustang GT auto. PI swapped. Daily beater

  25. #25

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    The green one switches over at 128F, more or less the same as the green non-switched one used for EGR.
    And more importantly, the switch is normally open (when the engine is cold) same as the red one you have.
    (The red one switches at 160F.)

    The blue one also switches over at 128F, but the switch is normally closed. Not what you would want, unless
    you just want the upshift light to work when the engine is cold.

    Your '85 should actually have a pair of vacuum switches on a bracket on the back side of the driver side strut
    tower. One controls the upshift light, the other controls the TAD solenoid. If yours is gone, someone's probably
    "cleaned up" your your engine bay, without understanding what any of that stuff does.

    The upshift light will still operate without the vacuum switch, but it will always tell you to upshift at ~2000 RPM
    whether you're cruising or at WOT. The vacuum switch closes to inhibit the light when manifold vacuum goes
    below 3"HG.
    Cheers,
    Jeff Cook

    '85 GT Hatch, 5-speed T-Top, Eibachs, Konis, & ARE 5-Spokes ... '85 GT Vert, CFI/AOD, all factory...
    '79 Fairmont StaWag, 5.0, 62K original miles ... '04 Azure Blue 40th Anny Mach 1, 37K original miles...
    2012 F150 S-Crew 4x4 5.0 "Blue Coyote"... 65 coupe, 289 auto, Pony interior ... '67 coupe 6-cyl 4-speed ...
    '68 Vert, Mexican block 307 4-speed... '71 Datsun 510 ...
    And a 1-of-328 Deep Blue Pearl 2003 Marauder 4.6 DOHC, J-Mod, 4.10s and Lidio tune

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