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Thread: Dash Lights Too Dim??

  1. #1
    Join Date
    Dec 2012
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    topanga CA
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    84 728i,325Ci, 77 R100RS

    Dash Lights Too Dim??

    1984 728i.

    So I'm in the dash today - inside the headlight/dash rheostat switch to be exact - trying to pick up the dash light dimmer wire to feed the new boost gauge light at night. I only found one wire on the switch that my test light, which was grounded to the dash, responded to dimmer-wise. It's the one off to the side by itself if you pop the rear cover off the switch. It measured a range of 2 to 8 volts at the extremes of the dimmer wheel. OK, maybe it's only supposed to have 8 volts so it doesn't blow the bulbs or something. So I picked up that feed and a ground and wired the boost gauge bulb ... and it looked OK, dimming as the wheel was turned.

    Tonight when I go out for a test drive I discover that the boost gauge only lights UP when the dash is dimmed DOWN. And (not new today) unless you're out on a dark road, the dash lights are all too dim. It's been like that since I got the car...which is a USA conversion, converted back to euro lights, with a big stereo with GPS and phone, etc, plus a remote locking/alarm rig, a turbo, methanol injection, a wideband, etc. So there's enough non-factory wire under the dash to build another car.

    So WTF?

    Should I have 12v coming out of the dimmer turned all the way up? And how did I get the boost gauge light going backwards? I'd like to get all this cleaned up once and for all. If I need to change the dash bulbs or voltage I'm good with that.

  2. #2
    Join Date
    Jun 2010
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    TX
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    4,487
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    1983/84/85 745i
    I swear the ground changes or some goofy shit when I was trying similar. Try tapping into the ashtray light or that plug for the headlight leveling.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  3. #3
    Join Date
    Dec 2012
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    topanga CA
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    84 728i,325Ci, 77 R100RS
    So 12V is OK for dash lights? No melting or big fires?
    Last edited by andyleonard; 02-05-2018 at 11:37 PM.

  4. #4
    Join Date
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    1983/84/85 745i

    Thumbs up

    Been about two years since I messed with it and trying to make my boost gauge dim. I will have to think on it and remember how it works, I just removed the damned bulb for now as too bright.
    I make E23 parts.
    09/1983 745i (stolen spring '13 around Houston, TX Achatgruen on nutria buffalo. 8481080)
    10/1984 745i
    11/1984 745i
    11/1984 735i (10:1-265/6)
    Ford, MB, and GM round out the pack.



  5. #5
    Join Date
    Dec 2012
    Location
    topanga CA
    Posts
    483
    My Cars
    84 728i,325Ci, 77 R100RS
    Quote Originally Posted by Hit Man X View Post
    Been about two years since I messed with it and trying to make my boost gauge dim. I will have to think on it and remember how it works, I just removed the damned bulb for now as too bright.
    OK I'm pretty sure the boost gauge issue is licked: solder boost light wires to the contacts of the lamp sticking out the back of the headlight switch, the backlight lamp for the ON-OFF positions. Seems to work.

    Still picking at the dash lamp dimmer and dim dash bulbs issue. It seems the dimmer works on a ground and doesn't dim the positive. I was getting 8V to ground off the dimmer turned all the way up so I gave it 12V and it blew the fuse. ???

    We'll see what's what when it gets dark.

    Here's an odd one. When I tested the little boost gauge lamp on the rheostat it was pulled out of the gauge and all was good. Once inserted in the gauge it grounded to the dash through the mount and screws and the rheostat quit working. I had to isolate the lamp holder from the gauge mount for dimmer to be effective.

    Jury's still out on whether main dash has 12v now.
    Last edited by andyleonard; 02-09-2018 at 05:48 PM.

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