Author: Bad Boy Bobbers & Customs   Date Posted:7 March 2018 



There are loads of Motorcycle Tachometers available however the specifications vary as much as the designs. We often hear people who own XVS650's state they feel that their bike isn't ideal for the freeway as its revving its head off. We have ridden the same model bikes without having this experience so really wanted to drill down & figure it out.

As any XVS650 owner will know, the speedometer is the only gauge fitted by the factory. The latest Bobber turned out by Bad Boy Bobbers is a shop bike for ourselves & features loads of custom parts including a Sportster tank. Fitting the Sportster tank eliminated the factory speedo. We fitted this bike with 1 1/4” Harley fitment T-Bars courtesy of the T-Bar adapter we are now producing to suit Yamaha XVS650's. The T-Bars don't have any dash mounts so we sourced a dash mount kit for the T-Bars.

Once that was installed we proceeded with our plans to install a new Speedo & a new Tacho side-by-side. Finally we would get a true reading on the RPM's.

The new Speedo is cable driven so connecting the cable was a no brainer. The speedo also houses the Neutral, High Beam, Left & Right Turn lights & LED Back lighting and earths for each so there was a lot of wiring to be connected and no colours matched. Interestingly the only challenge encountered when wiring the speedo was the neutral light stayed on when the bike was placed in gear but the LED back light went out. Sounds like a simple case of two wires being swapped or so I thought. After cutting the harness open so I could access the individual wires I found the Neutral & High Beam lights to be connected correctly. Okay..... what else could it be? I hunted in the harness with a test light for ages, checking for power supply to the individual lights & also checking for good earth connections.

It was checking earths where I made my breakthrough. The dash wiring harness had no less than 4 black wires, 3 out of the 4 of which tested as good earths. What I would eventually discover was that one of the earth wires changed from active to inactive when the gear selector was moved between neutral & first gear. Once I had the neutral light connected to 1 particular earth wire, everything functioned.

I have zero formal training in automotive wiring. Everything I know about wiring I have learned from my two best teachers, Trial & Error. Installing the new compact speedo was a trial and I made errors but eventually I achieved success.

The next task was to install the compact Tachometer which had a total of 5 wires. There were 2 thin wires, one red & one black which I guessed correctly were for the LED back light. That left 3 wires with male bullet connecters. I recall back in my youth I tuned a lot of cars using an automotive multimeter to set various parameters such as idle RPM, points dwell and somewhere in my rearview mirror I remembered the multimeter being connected to the coil. I also know coils put out substantial voltage, can give you a nasty jolt & can be shorted causing electrical damage so before I jumped in I decided to do some homework. Time to hit google up.

Forums are a wonderful source of both information & misinformation & I followed more than one bum steer before turning to YouTube where I found some relevant videos giving me the fundamentals of connecting a tacho to a V-Twin Yamaha. Two of the videos were particularly helpful but, of course the colours of the wiring on their tachos were different to mine & most of them were dealing with 4-wire tachos, where mine was a 5-wire. Its never that easy is it!

As mentioned I isolated the 2 thin wires leaving me with 3 tachometer wires. 2 of the wires would be connected to the coils positive & negative terminals & the 3rd wire needed to be earthed.

Okay – but which ones?

Using my white board I made notes of which colour wires I was connecting and tried all the possible combinations with no success. I was using an earthed test cable for my earth so the only other variation I could think of was to get my earth from the mounting screw on the coil. Once again I set out to try all the combinations but on my second connection the tachometer jumped into life and sat around the 1000 rpm marker. Success!! I photographed the current wiring arrangement whilst I had it all functioning as I learned a long time ago, what seems will be easy to remember is gone when you need it. My phone does not suffer the same memory problems as I do & I'd rather take 10 photos & not need them than forget to take a photo when I do need it.

So I have the tacho working using test cables (cables with Alligator clips on either end) and now I just need to make permanent connections to the relevant wires & terminals. This took time as I had to splice into the positive & negative coil wires and make an earth cable with a post connector to the mounting screw. The LED backlight wires needed to be wired into the bikes dash harness.

Once all of this was done I fired the bike up expectantly . The lights were on but nobody was home, the tacho needle didn't move. :-(

I knew I had the wiring sequence correct so using a test light with a probe I began testing the tacho side of all the wiring and discovered a bad connection. I removed the connector from the terminal, cleaned both and reconnected and tested again, the wire was live! I started the bike again and was very happy to see the tacho working & when I revved the engine, so too moved the tacho.

What did I learn? I learned that the wiring diagrams you get are almost useless and often the information is misleading or wrong. I learned how a tacho needs to be connected to a coil but unless I was using the exact same tacho again, its likely I would need to use the trial & error method on the 3 wires until I got it right. The great time saver is the knowledge that I cannot pick up any earth, even one running directly to the negative terminal on the battery, I have to get my earth off the coil mounting screw.

We have developed & will be releasing a T-Bar & Adapter kit for the XVS650 as used on this bike and also a Dash Relocation Kit for same. We will offer the speedometer alone and a dual gauge kit with the speedometer & tachometer. We will do our best to provide the most comprehensive wiring instructions possible but when it comes to wiring, there are gremlins at work against you. Poor connections, broken or dead wires, power back-feeding down earth wires, amperage change caused by connecting 2 different diameter electrical wires & all sorts of craziness designed to fry your brain cells. Many people run for cover when the word “Wiring” is mentioned and I don't blame them. I'm not sure if I'm tenacious, obstinate or just damn stubborn but I MUST figure these things out or I cant rest.

To be honest, a full days worth of work would have been consumed configuring, installing & wiring the two new gauges. How could a customer understand 8 hours labour to fit a dash? They couldn't & if they could, they would be doing it themselves. There may be some electrical geniuses out there who could have completed the work I did with one hand tied behind their back and had it finished in 10 minutes and if so then good luck to them, they don't need to read this. I write these blogs to help the average guy or girl who wants to customise their motorcycle & wants to do the work themselves.

Good luck with your wiring, if I could give you one final tip it would be to walk away or do something else when it all gets too confusing. Coming back to it with a fresh pair of eyes & clear mind will often reveal issues you just couldn't see before.

From the team at Bad Boy Bobbers & Customs.


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