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Thread: HELP!! Speedhut inverter/dimmer

  1. #1
    Senior Member Higgybulin's Avatar
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    HELP!! Speedhut inverter/dimmer

    Has anyone had one of these go bad? I am wiring up my dash with the RF harness and can get the pointers to work with the red/blk/white ribbon but can't get the backlights of the gauges to come on with the white/blk wires no matter what I do. Wiring is not my forte so if there is a way to test it I'll be happy to try that. I have tried direct blk/white to a 12V jumper. I did buy the gauges used but was assured they worked. Any help would be great!!
    Higgy
    Last edited by Higgybulin; 12-10-2019 at 11:17 AM.
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  2. #2
    Senior Member edwardb's Avatar
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    Yes, the inverter has been known to be defective and/or fail. The version of the gauges that uses the inverter (there's apparently a newer version that doesn't...) won't light the AC powered backlighting without it. So direct wiring with 12V DC won't do anything. Ideas? Make sure the knob on the included little potentiometer is turned up. Make sure the knob on your headlight switch is twisted all the way clockwise. The dash gauge lighting circuit goes through the dimmer function on the headlight switch. Sometimes guys have that knob turned down to where the gauge lighting doesn't have enough voltage to light. The inverter needs the proper DC voltage in. Start there for the obvious possibilities. Next steps would be to start probing with a VOM. If you have to call Speedhut, I've found their customer service is very good.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
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    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

  3. #3
    Senior Member Higgybulin's Avatar
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    Quote Originally Posted by edwardb View Post
    Yes, the inverter has been known to be defective and/or fail. The version of the gauges that uses the inverter (there's apparently a newer version that doesn't...) won't light the AC powered backlighting without it. So direct wiring with 12V DC won't do anything. Ideas? Make sure the knob on the included little potentiometer is turned up. Make sure the knob on your headlight switch is twisted all the way clockwise. The dash gauge lighting circuit goes through the dimmer function on the headlight switch. Sometimes guys have that knob turned down to where the gauge lighting doesn't have enough voltage to light. The inverter needs the proper DC voltage in. Start there for the obvious possibilities. Next steps would be to start probing with a VOM. If you have to call Speedhut, I've found their customer service is very good.
    Paul, does my headlight switch need to be in the mix. I put the 12V right to the blk/wht wires on the inverter, and played with the dimmer switch
    New MK4 kit picked up 4/10/23!!!
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  4. #4
    Senior Member Avalanche325's Avatar
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    I had one go bad. The replacement was a newer version.

  5. #5
    Senior Member edwardb's Avatar
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    Quote Originally Posted by HiggyMK4#9579 View Post
    Paul, does my headlight switch need to be in the mix. I put the 12V right to the blk/wht wires on the inverter, and played with the dimmer switch
    My response was assuming you had the dash wired. My bad. No. The headlight switch doesn't add anything if you're applying power directly. You can bench test the gauges. I assume you have all the gauges wired together with the supplied daisy chain cables. The black and white wires for the inverter should power the backlighting. Turning the pre-wired potentiometer should adjust the level. The 3-wire cable does the rest. Red = gauge power, white = pointer lighting, black = ground.
    Build 1: Mk3 Roadster #5125. Sold 11/08/2014. Build 2: Mk4 Roadster #7750. Sold 04/10/2017. Build Thread
    Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020. Build Thread and Video. Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020. Build Thread and Video
    Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023. Build Thread. Sold 11/9/2023.

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    Senior Member Avalanche325's Avatar
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    12 VDC in 100 VAC out

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  9. #7

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    Just a tip here. First car we used the Speedhut gauges in we tried the gauge lights in the well lit shop and could not tell if they were working. Turned down/off all of the shop lights and what do you know, they worked.

  10. #8
    Senior Member Higgybulin's Avatar
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    Quote Originally Posted by i.e.427 View Post
    Just a tip here. First car we used the Speedhut gauges in we tried the gauge lights in the well lit shop and could not tell if they were working. Turned down/off all of the shop lights and what do you know, they worked.
    I definitely had the shop lights off, I think it's toast. Good news, as many have said before Speedhut has pretty good customer service! A new one is on the way.
    New MK4 kit picked up 4/10/23!!!
    SOLD
    MK4 #9759 picked up on 4/3/19
    351C, 3 link, 17's, dual roll bars

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