New tach not working.

jerryjerry05

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98 75hp 3cyl.
Runs ok.
The tach is new.
It's set right for the motor.
It does nothing on any other settings.
It doesn't jump or move when the motors started.
The leads from the motor
Black, grey, purple.
The grey and purple both have voltage. The purple is the power lead and the grey is the tach lead.
The grey is hooked into the rectifier and all 3 lugs on rectifier have voltage.
Hope I gave enough info.

Any ideas?
Thanks,Jerry
 

snowbrd84

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Since the gray lead has voltage, it sounds like a signal is being sent but the tach isnt responding? Did you verify the ground is good, gauge wont respond to tach signal without 12v power and ground... You say the gray has voltage, is that just with the motor running. i.e. it shouldnt have voltage with the motor not running... Are you sure the tach signal isnt just outputting a constant voltage where it should be sending pulses (maybe a crossed wire??)
 

jerryjerry05

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Motor not running, key off, 12v at the grey lead at/to the rectifier.
The tach doesn't jump or jiggle, nothing.
Ground is good.
All connections good.
 

snowbrd84

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The gray wire should not have 12v with the motor not running. The gray wire is on a rectifier post with a yellow wire right? The only rectifier post that should be 12v with key off is the + post with the red wire. The only time the gray wire should see voltage is when the flywheel is rotating around the stator, thus generating voltage pulses...

Those pulses are counted by the tachometer, the selector dial on the back of the tach is to let the tach know how many pulses equals 1 RPM since different charging systems generate different numbers of pulses per revolution...
 
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snowbrd84

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Maybe your rectifier is toast? Off the top of my head, and you may want to search around to verify, there should be very high resistance going from the red wire (+) post on the rectifier to the yellow wire posts. And very little resistance going from the yellow to the red. If there is little to no resistance going from the red to the yellow, then the battery is basically connected straight to your tach signal and it aint gonna work cause it just sees 12v all the time instead of a square wave pulse that it can count

On second thought, you should absolutely not have 12v DC on the gray wire. The stator outputs AC voltage, the rectifier (also know as a diode rectifier) converts the ac voltage to dc voltage to charge your 12v dc battery. The tachometer reads square wave AC voltage. Basically it is a pulse, it has high and low like this __---__---__---__---
 
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jerryjerry05

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On the rectifier: the middle post has a grey lead from the engine harness.
It goes to a grey lead up to the dash.
The grey from the engine harness has 12v
The top post has 2 yellow leads and so does the bottom post.
The top and bottom post(yellow leads) have 6v if the key is on or not.
I haven't unhooked the yellow leads to check voltage.

Anyone know how to test a rectifier?
 

snowbrd84

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A rectifier should have 1 post labeled "+" and that is the output to send 12V DC to your system and charge the battery (typically a red wire). There should then be one or two posts where the yellow wires from the stator hook up to. Those yellow wires deliver AC current in pulses generated from the stator. The tach signal connects to the same post as one of the yellow wires. Those yellow wire posts are connected to the "+" post inside the rectifier with a combination of resistor, capacitor, and a rectifier diode. Current flows ONLY from the yellow to the red through that system while being converted from AC to DC voltage. Therefore, you should read little to no resistance going from yellow to "+". You should read very high resistance going from the "+" to the yellow. Its a one way system. Disconnect the yellow wires and leave only the red wire on the "+" post. You should then measure 12v DC on the "+" post. Then measure the yellow posts, they should read nothing. If you get voltage on the yellow posts at that point, your rectifier is bad and needs to be replaced.
 

snowbrd84

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Before you do anything, disconnect the gray wire from the rectifier and check it with a volt meter, it should not read anything. If it still reads 12v, it is connected to 12v somehwere and it shouldnt be.
 

jerryjerry05

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The way it's wired.
The voltage regulator has a grey lead that goes to the rectifier.
It has 12v with the key off coming from the VR it goes to the rectifier and to the tach.
There are 2 yellows from the VR that match/meet on the rectifier with yellows coming from the stator,
They both have about 6v. the VR has 2 red leads into the VR and both at 12v
 

snowbrd84

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There should not any voltage on the yellow rectifier wires or the gray tach wire if the engine is not running. Did not realize you have a voltage regulator as well. Disconnect it and see if that fixes the problem.
 

jerryjerry05

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I hooked it all back up.
The grey lead from The VR is supposed to put out about 8v when running.
It puts out a little more than 12.
The motor doesn't charge while it's running.????
 

snowbrd84

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You should have your voltmeter on the AC voltage setting if you are taking a reading on the yellow wires. Yellow wires are AC, the rectifier converts it to DC at the "+" post where the red wire connects. The regulator simply keeps the voltage down so that you are not sending more than 13ish volts to your battery... The regulator can fail and screw everything up, disconnecting it to test will not hurt anything. It is only there so that at higher RPM, when the stator is outputting more, you are not sending more than 13ish volts to your 12v system...
 

quicktach

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Sounds like you're not getting a tach input signal. You should have grey as signal..other two wires ...12 supply and ground to run the tach light. Did you follow wiring diagram with the new tach ? is there a fuse anywhere that may have blown ? Check continuity of grey wire.
 

jerryjerry05

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The continuity is good.
It's wired right.
The grey lead from the voltage regulator has 12v coming from it.
I have unhooked the grey lead at the VR and it has 12v at the VR.
I'm guessing but I'd say the VR is shot???
 
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