Getting a shock from tachometer
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Intermediate
Joined: Jun 2017
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From: Michigan
Getting a shock from tachometer
I start my bike and take a jumper wire and touch the back of the tachometer and the other end on the top of head light or any metal and the bike will shut off! I can tough the back of the tachometer with my hand and I don't get a shock until I touch something metal. The tach should be insulated, Correct? I took the back of the tach off and I don't see any bare wires anywhere.
Elite HDF Member
Joined: Feb 2016
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From: Pittsburgh
I start my bike and take a jumper wire and touch the back of the tachometer and the other end on the top of head light or any metal and the bike will shut off! I can tough the back of the tachometer with my hand and I don't get a shock until I touch something metal. The tach should be insulated, Correct? I took the back of the tach off and I don't see any bare wires anywhere.
The tach is floating at some VDC potential - I'd say there's a wiring fault within.
House circuits have a grounding plug to prevent electrocution? For arguments sake say you have a drill with a metal body and a dysfunctional grounding plug. Plugged in, you receive an electrical shock? What is occurring is that internally, there is a fault that allows the drill body to become 'floating' at some a/c potential. When you touch the drill body, your body provides the path to ground and you feel an electrical shock (maybe kill you depending on your grounding).
I suspect the tach has the same fault. Insulating the tach from ground doesn't do anything other than allowing it to 'float'. Any path to ground is basically shorting out the electrical system.
Road Warrior
Joined: Jul 2012
Posts: 1,566
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From: Londonderry, NH
I start my bike and take a jumper wire and touch the back of the tachometer and the other end on the top of head light or any metal and the bike will shut off! I can tough the back of the tachometer with my hand and I don't get a shock until I touch something metal. The tach should be insulated, Correct? I took the back of the tach off and I don't see any bare wires anywhere.
Elite HDF Member
Joined: Feb 2016
Posts: 4,133
Likes: 452
From: Pittsburgh
Most digital circuits require a good ground to operate, it prevents ambiguous logical (electrical) states? That is not what is happening here - the entire device is floating at some VDC potential? It's dragging down the entire power grid when you provide a ground. I'd suspect the tach.
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Intermediate
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From: Arkansas
Grounds are typically located just aft of the fuel tank under the seat. Otherwise other things are just frame grounded.
Road Warrior
Joined: Jul 2012
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From: Londonderry, NH
You can easily varify a ground fault by running a jumper from the fork tree (upper or lower) to the frame.