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Tach inop

the_elder_rocker

the_elder_rocker

Silver Level Sponsor
HI Folks-
After finding the tach to coil wire attached to the wrong terminal on the ignition switch (Was plugged in with the whi/red solenoid wire), and attaching it correctly I now have the right wire on the coil (more about this later) and still have no tach operation. Yes, the wire is looped through the plastic piece, the metal stirrup shaped piece is attached and contacting the contacts at the tach and the tach is grounded, as evidenced by the light working fine. Thing is, with the car running the tach will jump as I tap on the body of the tach with the butt of a screwdriver. Might it just need time since it had obviously been a very long time not operating? Does the nut attaching the metal stirrup to the stud need a fiber washer to insulate it? Is the tach just pookah? Any advice appreciated. Now on to the white wire conundrum-- The car was running with a different white wire. It came out of the firewall in a large harness with a bullet connector. Hot when key on. The correct wire that was wired incorrectly to the solenoid terminal on the ignition switch would be hot when key on but not when start activated. Moving it to the correct terminal on ign. switch cured that. Verified that it was correct wire by unhooking pos terminal on the battery, unhooking wire from ignition switch, jumper to batt positive, test light on coil end terminal and piercing wire covering at tach- all lit up w/ test light. All's right with the world- but---- what is the extra white wire? All I can figure based on the (Excellent!) wiring diagram in living color is that it is an - unused- overdrive feed. Am I way off? At worst I figure it would power a radio when I get to that point. If you made it this far I thank you. Any feedback on the wire? Couldn't resist the pun.
Mike Burgess
Albert, KS
 
Sounds like the white wire is the overdrive feed. Here is where the factory left the white wire for the overdrive wiring on my Series V:
1767635611920.png

As to the tach - did you coil the wire loop in the correct direction? Did you try adding another loop?
 
Looks like the same location as the mystery white wire on my SV. I just left the wire coiled as it was when I started. I noticed a couple of times when I tapped the tach body the needle jumped to 1500 rpm or so. Strong believer in Repair Procedure Number 1- whack it! I will dive a bit deeper on that- The car sat for a very long time before I got it- an unfinished project with VB parts dated 2009--- then the guy I got it from is a Harley mechanic- home schooled- it didn't run at all- need I say more?
Thank you!
 
The tach is electronic, so banging on it probably not a great idea. Try adding one more coil to the loop. If that doesn't work, try reversing the loop coil direction.

Here is an old picture of the back side of my tach:
1767637904624.png
 
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Yep- that's what I see (with a hand mirror) when I look back there. I'll dig into the looping next time I get out to the shop. Oh- I'm just tapping the tach body- I save the hammer for the carbs of course!
Thanks again!
 
Was your car originally positive earth or negative? These tachs are polarity specific. The tachs can be converted though to work on whatever polarity your car is.
 
Is it possible that the tach is just so out of calibration you are getting this anomaly? I was able to stop the tach in my Tiger from jumping all over the place and being useless by adjusting the adjustable resistor inside. I took off the mounting nuts and had enough wire length to bring it out the front of the dash enough to get to the back of the tach. By removing the light bulb socket, I could see the adjustable resister and was able to rotate the body of it with a small screwdriver pushing on the side of the adjustable resistor. Only needed to move it about and 1/8 inch of rotation. I then fine tuned it at about 2,000 rpm against a meter on the coil. It instantly fixed my issue. Not my idea. Read it somewhere. Hope this helps.
 
Hi Guys- Thanks for the replies on this. Terrific info. Since my post on the tach I haven't started the car. The dash was mud-fence ugly and the wiring behind the dash was misrouted so---- out came the dash, It's got a nice veneer on it now and the wiring is much easier to work with. Working on recovering the bottom padding and lubing/ recabling/new heater control valve/cable..... Aaah, mission creep!
 
The white wire loop only works one way round. It has to be wound exactly as shown in the WSM. Make sure that you have it wound that way before trying other suggestions.
Tim R
 
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