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Discussion Starter #1
So over the winter I stripped my 748 down to the frame, powder coated it and put it back together. I never noticed this before the strip down and I double checked all my wiring so I'm not sure what it could be. Whenever I turn on either directional my tach will jump up and down as my blinker flashes. It will do it all throughout the rev range and at idle. I have LED integrated tail lights and another set of blinkers in the tail screen vents. I thought that it might have been the LED causing the problem so I disconnected them and left the bulb type ones in the tail vents but nothing changed. The first time it happened it was actually bogging the bike down and ended up blowing the fuse. I found one of the wires going to the LED tail light was pinched. After I fixed that the bike wasn't bogging down and the fuse wasn't popping but the tach was still jumping. Any ideas?
 

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Old Wizard
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Electronic tachometers give erratic readings when the base voltage is low, usually caused by a loose battery connection. The worse situation for low voltage is at idle when the alternator output is at it’s lowest. You may just need a new battery or a good charging.

If it's not the battery:

Most likely - Intermittent power or ground connection
Next likely - Intermittent rpm signal connection
Least likely - Tachometer internal problems

Check for a loose or corroded electrical connection at the battery, the fuse, and any in-line connector. Check the two battery connections first, next the connector at the instrument cluster, then at the fuse, and lastly at the wiring harness connections. Check the three brass ground screws on the back of the tach for tightness.

Next, since the bike is running OK, the RPM sensor gap, the sensor itself, and wiring back to the computer are not the problem. So you need to check the connectors between the computer and the tach.
 

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Check your grounds, the tach and turn signals share the same black ground wire going through the big circular connector. Chances are the ground connection through the conner are flaky. To check; land a volt meter between the negative battery post and the black ground wire servicing the tach and blinkers. If you see more than than a 0.5 volt rise on the blinker ground you've nailed the problem. Also keep in mind some LED blinkers include a shunt resistor to insure the LED's draw sufficient current to trigger the old fashion thermal blinkers. If this resistor is too small [read low resistance] then the blinkers can draw more current than the electrical wiring was designed to handle. Again check this by landing a volt meter between the the black ground and the 12v [LB light blue] because again they share the same 12v light blue wire.

Good Luck..
 

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Super Moderator
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Check your charging system (see my write up in the Hall of Wisdom)

I had that exact same symtoms on my -97 748 when the yellow wires and V/R connector had burned out. The tach jumped with turnsignal pulses all through the rev range. Fixed it and it stopped.

//amullo
 

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Discussion Starter #7
Check your charging system (see my write up in the Hall of Wisdom)

I had that exact same symtoms on my -97 748 when the yellow wires and V/R connector had burned out. The tach jumped with turnsignal pulses all through the rev range. Fixed it and it stopped.

//amullo
I think this might be it. I found some corrosion inside the connector from the stator. I'm going to upgrade the wiring anyway so hopefully I'll kill two birds with one stone. Thanks everyone.
 
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