Final Important Update:Rewiring my 1975 860GT

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Parallel Twin
Posts: 137
Joined: Thu Dec 05, 2013 10:54 am
Location: Malabar, Florida

Final Important Update:Rewiring my 1975 860GT

Post by rjk40 » Thu Oct 02, 2014 12:08 pm

Two items: one easy substitute, one mystery

First Item: In retrofitting the universal switch into the left side to replace the rotten original, item KS12-0030L at Bevel Heaven (nice item, Steve), I had trouble getting the blinkers to blink, after confirming, with meter and jumper wires, that I could light them all up statically, I eliminated everything but blinker the relay in the headlamp assembly. I was able to get the lights to flash, but very weakly with the original relay when compared to using jumpers. Looking for a rational substitute and finding nothing obvious online, I fitted, in desperation, a cheap NAPA 552 blinker relay, as my old Chevelle uses, and the blinkers blinked nicely. So, there is an easy substitute. Time will tell to see if it lasts. Cost: about $3.00 US four years ago.

Second item: I am unable to get the yellow dash blinker indicator light to blink with the right turn signal, even though both the front and rear blinkers light up. All is well with the left signal, both the front and rear blink, as does the yellow indicator on the dash. In looking at the wiring diagram, it appears that only the left blinker circuit goes to the yellow dash indicator, and not the right. Can this be for real, or am I nuts? Tracing the circuits with a meter shows the same thing. It's been 30 years since I rode this bike, so I cannot remember what worked. Can this really be a wiring error, or a brain error on my part?

After looking further into the wiring diagram, I have found that the blinker indicator is not, as typical, wired to ground on one side plus an energizing signal, but one lead goes to the "hot" side of the left front blinker and the other side goes to the "hot" side of the right front blinker. As I have retrofitted LEDs into the dash, and since they are not bidirectional conducting as is an incandescent bulb (they are semiconductors and only pass current in one direction), I believe that I must, perhaps, put in diodes into each leg that feed the new LED indicator, to isolate one blinker side from the other. As this is a work-in-progress, I can experiment.

As I suspected, if I swap in an incandescent lamp into the spot for the blinker indicator, taking out the LED I just put in, the indicator flashes when EITHER left or right turn signals are switched on.

Am I missing a wiring update? Steve? Comments? Am I the only person who has had this problem when retrofitting LEDs into the dash?

But, if any of you have been here and can share some advice, I am grateful.

I was pointed to the manufacturer of the LEDs, Damien Birch, by Steve. Here is the final word from the source. It should be fairly explanatory:

Hello Richard, when fitting any of the ducati bevel twins with LED dash lights where the bike has direction indicators, you have to fit a diode bridge on that one LED. It's a very simple device that will keep a constant polarity to that LED. See here; ... cts_id=154

This should save all of you who are retrofitting LEDs into your Ducati 860GT dash, the time I wasted coming to the same conclusion without this information.


Richard Kovach
Malabar, Florida

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