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General Category >> Rubber Side Down! >> Tach wiring problem
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Message started by Keifer on 03/25/21 at 11:54:33

Title: Tach wiring problem
Post by Keifer on 03/25/21 at 11:54:33

I bought the generic tach like everyone else has here (like the old RYCA or drag specialties one).. but no logo. Has 4 wire, meant for the waste spark system... been through the tech section.

I hook blue and red to horn, black to ignition coil mounting screw, and green to the black/yellow on the coil itself. It's not working.... it gets power (does the needle sweep) but not registering any RPM.

Is there another way to wire these 4 wire tachs?? Why am I having an issue here it was supposed to be dead simple... :-?

Title: Re: Tach wiring problem
Post by TheBrendan312 on 03/25/21 at 12:08:48

I just wired mine up a few days ago and had no issue.

I would double check both of the wires on the coil, make sure you have the black wire screwed down around the wire itself and not the insulation.

If that doesn't work it might be a faulty Tach and I would try to exchange it.

Title: Re: Tach wiring problem
Post by Keifer on 03/25/21 at 13:20:35

If it’s getting power (from the needle sweep at startup) the ground should be proper right? So it’s just not getting signal from the green wire? Maybe you’re right could be a defective unit...

Title: Re: Tach wiring problem
Post by TheBrendan312 on 03/26/21 at 04:30:18

yeah, if you have double and triple checked all your connections that's what I would think, that is assuming you bought the right tach.

do you have a link to the one that you bought?

Title: Re: Tach wiring problem
Post by Keifer on 03/26/21 at 04:52:19

This is the one:

https://www.ebay.ca/itm/MOTORCYCLE-TACHOMETER-FOR-ALL-DUAL-FIRE-IGNITIONS-HARLEY-TACH-UNIVERSAL-FIT/350956583289?hash=item51b6a47979:g:6~IAAOSw9SdeL5aa

If my ground is bad, the whole tach would not work, correct? It's just odd I'm getting power but no green wire signal. I guess I'll try and take apart the tach once the weather improves here... too late to return it.

Title: Re: Tach wiring problem
Post by oldNslow on 03/26/21 at 07:46:46

According to the link you posted that tach is made for a Harley and the green wire is supposed to be connected to the VSS (vehicle speed sensor) not the coil. Harleys have a sensor plugged into the transmission that reads the speed of the transmission output shaft in order to drive the speedometer.

That tach may not work on a Savage..

Title: Re: Tach wiring problem
Post by TheBrendan312 on 03/26/21 at 07:53:11

142A2B27352928460 wrote:

This is the same Tach that I ordered, works perfectly fine on my bike.

I would assume that the tach they received is faulty ~~and I would return it to the seller.~~

Sorry, didn't finish reading the rest of the posts

Green is not for the ground, the black wire is for ground, green is supposed to go to the negative terminal on the coil according to the diagram that comes with the tach.

Title: Re: Tach wiring problem
Post by Keifer on 03/26/21 at 09:44:41

I may have worded incorrectly... but yes I have black to ground.

This seems like the same tach that every company stamps their own logo on... I assumed the reference to VSS was generic speak in an ebay ad. The diagram that comes with the tach even shows it connected to a coil.

Title: Re: Tach wiring problem
Post by TheBrendan312 on 03/26/21 at 11:50:07

Right, this tach reads coil pulses for its measurement, luckily its not super expensive if you feel like buying another since you said its too late to return.

Title: Re: Tach wiring problem
Post by DragBikeMike on 03/26/21 at 19:20:17

Are you 100% confident that the green tach wire is making good contact at the coil? The black/yellow wire connects to the spade connector on the top. How are you making the connection at that spade connector?

For reference, I measured the resistance on a known good tach.

The resistance across the black and green tach wires is 112K ohms. It is not polarity sensitive, same reading either direction.

The resistance across the red/blue and green tach wires is 143K ohms. It is not polarity sensitive, same reading either direction.

The resistance across the red/blue and black tach wires is 27K ohms. It is not polarity sensitive, same reading either direction.

To be safe, I would not use an analog meter to check these values. Use only a digital multi-meter to avoid damage to the internal circuitry.

Title: Re: Tach wiring problem
Post by Yoshi on 03/27/21 at 05:07:20

I use the same gauge

Hook up red and blue wires to one side of the coil, green wire to the other side of the coil and black to the ground on the coil

Title: Re: Tach wiring problem
Post by Keifer on 03/28/21 at 05:59:59

Couldn’t get any resistance across the green wire it was infinite, must be a defective gauge. It’s also impossible to disassemble without destroying it... ah well I’ll bite the bullet and try another one.

Title: Re: Tach wiring problem
Post by justin_o_guy2 on 03/28/21 at 06:24:17

I'd hafta autopsy it. A Dremel with a cuttoff is handy. You might be able to fix it. It wouldn't be something for the road, but it might be helpful around the shop.
Whether it can be fixed or serve any purpose ,I'd still just Have to look inside.