Speedo lead wire?

[map747]

I wanted to change the speedo on my 1980 Gs1000Gl with a 1983 140 mph unit. There are an extra set of wires on the 85 mph speedo. I belive it is called the speedometer lead wire. What does it do? Is it for the self cancelling turn signals?

[Steve]

Yes, that would be correct.

Your signals will still flash, but you will have to cancel them manually.

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[map747]

Do you know how it works?

[Steve]

Yes.

There is a magnet on the driven disk inside the speedo. There is a small reed switch attached outside the speedo that is activated by that magnet as it rotates. Power is sent from the Turn Signal Control Unit (TSCU) through one of those two wires, then through the switch. The pulsed power is then returned on the other wire to the TSCU, which then applies its logic to determin when to turn off the flasher.

It is somewhat important to note that the flasher unit itself is NOT something you will find at your local auto parts store. Yes, it has three terminals and looks pretty much the same, but is rather unique amongst all vehicles. Of the three terminals, one is power in, from the battery. One is the pulsing output that goes to the turn signal lights. The third terminal is a signal wire that comes from the TSCU. There is a small relay that is built into the base of the flasher that determines whether the unit will flash or not. It does not actually do the flashing, it only allows it to flash. The signal from the TSCU is removed when the bike has travelled more than 10 MPH for more than 10 seconds.

I would have to do some testing to see if the TSCU will allow the signals to flash without the reed switch. If it doesn't, and you don't mind cancelling them manually, you can replace the flasher with a two-terminal 555 flasher. Easy and cheap solution.

However, if you want to retain your self-cancelling signals, it's going to take some effort, or at least the proper speedo unit that has the magnet inside.

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