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Fixing The Dash Lights On A 1981 Ducati Pantah

Discussion in 'Vintage' started by Saltspringer, Sep 20, 2020.

  1. After I installed a fresh battery my 1981 Ducati Pantah, I found that none of the lights on the dash worked. Ironically, the only bulb that I later found still functioned was the neutral light, and that seemed to have a switch issue at the transmission…

    I decided to replace the bulbs with LED’s and took a few photos in case anyone else is contemplating a similar fix. It’s not a difficult job, you just need to take things a little slowly, and be methodical and careful.

    This is the original dash, pretty tired looking and in need of some paint.

    20200915_143450.jpg

    The original lamps are not designed to be disassembled, I guess back in the day if one blew you just replaced it with a brand new unit.

    I photographed the wiring, made notes regarding where the wires were attached, and then carefully disconnected everything. I found the previous owner had made a repair to the wires going into the rear of the ignition switch, using insulation tape and gobs of silicon, so all that was stripped off and proper bullet connects reattached.

    There are two types of warning lamp, a round style and an oblong block; both can be disassembled with care.

    The oblong blocks appear to be very lightly cemented at each corner. You need a very sharp blade and to carefully cut about 2 mm back from each corner. After you have freed up the white base you should be able to work the colored portion of the warning light off, to reveal the incandescent bulb.

    The round lamps, used to indicate neutral and oil pressure, can be disassembled, but you need a Dremel to cut through the plastic where the colored portion of the lamp meets the clear portion at the base.

    20200918_104543.jpg

    Start by cutting the assembly across from brass electrical connector to brass electrical connector. Gently flex the coloured portion of the lamp and it should break free of the base. If it is being stubborn, gently cut across each electrical connectors. Flex the two parts again and they should separate. These two fittings seemed more fragile than the oblong lights, so take a bit of extra care.

    Once you have opened up both types of lamp, remove the old incandescent bulbs and any wiring strands that are still attached to the solder.

    20200918_113541.jpg

    Attach the new LED to the exposed contacts.

    20200918_115058.jpg

    I am sure everyone knows LED’s are polarity sensitive, if you connect the 12v to the cathode they don’t light up. No damage results, you just have to reverse the wires to get the lamp to light.

    The anode/cathode orientation is slightly less important for the round lamps, because the two connectors are so close together that they can be swapped very easily.

    The LED’s I used have a built-in resistor and are designed for 12v automotive applications. The positive (anode) leg of the LED was slightly longer than the negative (cathode) and I used this to orientate the LED’s when installing in the oblong lights.

    With the oblong warning lights, once I had separated the white lamp bases I carefully drilled two holes.

    20200918_121154_Burst01.jpg

    I then threaded the LED legs through the holes and pulled the wires, left and right to the brass connectors. The anode needs to go to the positive side of the electrical connection and the cathode attached to the negative or ground electrical connection. In most cases the black leads to the lamp were ground and the coloured leads were the positive connections.

    When you are wiring these up it is best to try and replicate the original positive and negative wiring; space is a bit tight under the dash cover and trying to pull electrical wires around to new locations is just a headache you don’t need.

    Once the LED was installed, I slid a very small piece of shrink wrap onto the exposed legs and then soldered the legs to the base of the electrical spade connector. The shrink wrap is probably not required, but it was easy to do and does insulate and provide a bit of mechanical protection to the exposed wire.

    20200918_133408.jpg

    I put a smear of red goop in the LED legs as they exited the mount to provide a tiny amount of vibration support. It is probably unnecessary.

    Simply repeat this for all the oblong lamps in the dash.

    The only exception to the single-LED-per-oblong-block pattern is the direction indicator/flasher. This light needs two LED’s installed, since both wires coming in from the loom are considered positive; one side for the left flashers and the other the right. This lamp looks like this.

    20200919_170832.jpg

    Before I reinstalled the dash, I tested the LED’s by connecting up a 12v power source to the lamp pair’s pins in the main harness plug.

    I found that the LED’s were extremely bright and decided that riding with the two lamps that are lit the most; the “Lights” lamp and the “High Beam” lamp, would be distracting.

    I made two, small plastic masks that were cut to fit the dimensions of the interior top of the oblong warning lights. I cut the plastic from a yogurt carton lid and gently pushed them down inside the colored lamp fitting. These masks drastically reduced the amount of light shining through and it was much more restful on the eyes.

    20200919_190629.jpg

    I am sure that there are many sources of LED’s. I bought some from Digikey for about $1.50 each and they worked fine. I am sure that anything that meets these specs will be good too.

    https://www.digikey.ca/en/products/detail/visual-communications-company-vcc/LTH3MM12VFR4400/6691214

    20200918_102718.jpg

    The dash went back together very easily and all the lights worked. I am going to assume that these LED's will last, once they are subject to heat and vibration. I will let the forum members know if in a few weeks they start to fail!

    Any corrections or additional advice from forum members will be useful for other owners doing a similar repair.
     
    • Like Like x 1
  2. Thanks for the detailed description and pictures, i will need to do the same
     
  3. Been a while but i finally converted the light to led's too, one thing that i couldn't figure out is the the indicator light.
    in the schematic it get's a + on each side wht\blk on one side and grn\blk on the other side.
    i don't understand where is "Ground" in this setup as both wires are supposed to have a positive feed according to the indicator working on that moment.
    a LED must get a (-) to work and has to be to a specific leg of the LED.
    how did you overcome this?
     
  4. Thank you @Saltspringer will bear in mind if i ever manage to get one.
     
  5. This set up only works with filament bulbs, the dash light returns to ground through the bulb on the non flashing side of the bike but the current is so low it doesn't illuminate the turn signal bulb.

    To solve the problem you need to fit a diode in each of the +ve feeds and join them both to the LED +ve and provide a new ground from the -ve terminal
     
  6. Thanks, i thought about grounding the LED negative side and connecting bote + feeds to the positive side, do i have to use diodes? which one can work here?
     
  7. On a related note, I used the kit now available for my MHR and am pleased with the result.
     
  8. Wont the current from the active side turn on the non active side if both + are connected together?
     
  9. By adding diodes to the + input to the LED you are preventing that but in reality the current will be insufficient to illuminate the bulb even though it is flowing through the filament to ground. If the turn signals use LEDs as well as the dash light you have to use diodes because LEDs, unlike filament bulbs, will illuminate when very little current passes through them.
     
  10. Hi Eran, apologies for the slow reply.

    I won't profess to being an electrical wizard, but the set up outlined in my original post seems to work. I can only assume that there is enough of a ground pathway through the wiring to the opposite indicator, to allow the LED to recognize the correct polarity and function. Since LED's are cheap and probably difficult to fry I would suggest just trying stuff out and see how you make out.

    If it doesn't work then look for alternative options. Best of luck and let us know how you get on!
     
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