Is my Tachometer dead?

[GhostMerc]

My tachometer quit working sometime last year.  I finally decided to tear into it a little bit to see what was going on.  My bike runs great, and starts almost instantly.  The tach will bounce a little bit, but not very much.  I started by looking for rust or corrosion and couldn't find any.  I decided to hotwire the tach straight from the coil. Below is how I went about doing this.  Still nothing.






Is my tach dead?  Is there a different way to wire this to check? Do I need to bust out my voltmeter?

[Pat Conlon]

Tach signal comes from the grey wire on your 2/3 coil (right side as you sit on your bike)
Check the continuity of that along with the black ground.

[GhostMerc]

I can double check my ground wire again.  I've got my yellow jumper wire ran directly from the first connector of the gray wire (I've got it squeezed into the connector in my first picture) to the tach.  I decided to bypass as much as I could first.  If my tach worked after that, then I'd start slowly working my way through the wiring harness.

I think I saw a post where Randy describes using this method.  I didn't see any pictures or hear any results of people trying this so I decided to give it a go.

If it is dead, I'm hoping I can find a functioning OEM.  Sourcing and installing an aftermarket does not look like fun.

[red]

I can double check my ground wire again.  
If it is dead, I'm hoping I can find a functioning OEM.  Sourcing and installing an aftermarket does not look like fun.

GhostMerc,

Hate to say the words, Search here (that's not my style), but I remember some outfit (in California?) was repairing the FJ instruments, and another outfit was putting in updated electronic gear which looked completely OEM.  Sure, there are also digital units (my preference) available, which fit the panel like OEM.  I would like to tell you more, but I have not contacted any of these guys, and I can't give you links (or old posts) to check any faster than you can do for yourself.  Maybe somebody here can chime in with more.  

Best.

[Firehawk068]

Ghostmerc,

I may have a good working spare Tachometer.
If you find yours is indeed "Dead" after testing of electrics, message me.
I'll look to see if I have it still, and I can send it to you.

Alan H.

[GhostMerc]

Ok, I did a few tests when I got home today.

1. Used my multi-meter to check original system continuity - Good
2. Checked voltage from coil ground to tach.
   A) AC
      1. Key on, engine off - 26V
      2. Engine low idle - 24V
      3. Engine high idle - 20.5V
   B) DC
      1. Key on, engine off - 12V
      2. Engine low idle - 10.5V
      3. Engine high idle - 9V

I read somewhere that the pulses from coil wouldn't register on the DC setting.  I tried both and got similar trends.

Conclusion: dead tachometer

[red]

GhostMerc,

You can have every voltage present and correct, but nothing works unless the grounding connections are good.  Run a temporary dedicated ground wire directly from the battery negative terminal to all the places where ground should be on the instrument panel.  Frame grounding can be bogus, and likewise the wiring that should make it happen.  If all voltages are good, and direct battery grounding is in all the right places, then you may have a dead instrument. 

Somebody here with an extra tach can probably provide the real Ohms readings across the instrument pins individually, from the ground lead to Pin 1, Pin 2, et c.  Then repeat the sequence, but starting from the Power pin, reading the Ohms value to pin 1, Pin 2, et c.  NO power is to be applied during these checks/readings.  A bad tach will probably show OPEN between the same pins that have a valid Ohms reading on a good tach.

I would bet on a grounding problem, sight unseen, because it is the most common failure mode of FJ tachometers that I have seen come by here.

Happy hunting!
.

[GhostMerc]

While I'm fairly certain my frame grounds are good, I've got the battery negative connected directly to the frame, I decided to run a ground wire directly from the battery to the tach.  Still no changes in performance.

I'll take a look at the wire diagram a little bit more and see if I can think of another test.

[red]

While I'm fairly certain my frame grounds are good, I've got the battery negative connected directly to the frame, I decided to run a ground wire directly from the battery to the tach.  Still no changes in performance.I'll take a look at the wire diagram a little bit more and see if I can think of another test.

GhostMerc,

IIRC, battery Ground goes into the instruments panel at several different terminals.  Those Ground terminals may or may not be interconnected inside the panel, but I have never had the instrument panel apart to know.

If nothing works, somebody here may have a good tach just waiting for you, or maybe they can give you the good Ohms readings from the Ground pin to the other pins, and from the Power pin to the other pins.  These Ohms readings are made with no connectors in place, and no power applied.  Beyond that easy stuff, I can't be any better help.
.

[FJ4ever]

Here's a post I did a while back on my wonky '92 tach. As of today, after thousands of miles, it's still working fine. Maybe you'll find it useful:

"Quote from: FJ4ever on July 24, 2017, 10:40:10 AM
After intermittently showing high revs for short spells, my tach started to continuously read almost double. Drove me mad. After checking out the coils and wiring I concluded the tach itself had to be the problem. So, out came the cluster and the tach mechanism itself, after getting hold of a working tach from an old 82 Seca 650 for cheap. After locating the corresponding wiring and setting up a fan to keep the engine temp manageable I started and warmed it up, set the engine speed to 3000 rpm on the Seca tach then shut it off and removed that tach. On the back of the FJ tach mechanism, top right, there is a rectangular white plastic resistor block with a round, slotted adjuster in the centre. I hooked the FJ tach up (holding it in my hand), started it up again at the same idle speed, adjusted the resistor with a small screwdriver until the tach read 3000 and shut it off and on a few times to ensure it was consistent, which it was. Cluster was reassembled and reinstalled, and it has been behaving itself for over a month. No ideas to offer on why a resistor should behave like that, but as long as it's working, who cares."

[Firehawk068]

Spare Tachometer 1990 FJ1200