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Tach issue

Meee

Member
Hi everyone, I have a mid 60's Thiokol 1404 V4 and put all new digital gauges in a new dash panel but I can't seem to get the tachometer to display properly. It has a switch on the back to select 4/6/8 cylinders. I do have it set to 4 but it doesn't read properly in any position. Anybody have a suggestion? Thanks.
 
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PJL

Well-known member
Where are you connecting the wires? The tach sense should be connected to the same wire on the coil that goes to the points.
 
some after market tach if its not set on 8 cyl. there is a wire that has to b cut----they sometimes have a small loop sticking out the back of the tach
 

Meee

Member
Oh yes, I think that is my problem and I forget to mention that I also added electronic ignition. No points. I'm hooked to the negative wire going to the coil as instructed by the tachometer instructions. This tachometer has a switch no wire loop to cut.
 
the tach should be hooked to the wire going to the dist.---NOT the power wire----and the coil has no polarity btw-----try putting the points back in----(and leaving them in----lol)----I ve had no luck with aftermarket kits----I would look into a crank trigger set up before a dist. update kit---many moons ago I would go to the junk yard and get a electronic dist. if I was working on a ford or dodge and use a chevy brain box out of a gm hei dist and wire it in line getting rid of the ford and dodge wiring mess----works great and a gm brain will adjust to a 4-6 or 8 cyl. on its own----my sv200 was bought cheap because of the aftermarket junk dist. kit that supported the halls system----pushed it on the trailer----got it home dug through the cab and floor putting the points back in and drive it off the trailer 3 years ago and still using the same points I found on the floor to this day
 

Cidertom

Chionophile
GOLD Site Supporter
If it is erratic reading, it needs a diode in line with the sense line.


(from the vdo troubleshooting guide) (I had to do this to my ST)
To Reduce or Eliminate Erratic Operation in Tachometers
1. Purchase diode #1N4005 from your local electronics store.
2. Cut both ends of the diode so each is approx. 3/ 4" long.
3. Crimp a 1/ 4" female spade connector on the end of the diode with the
silver band.
4. Crimp a butt-splice connector on the other end of the diode.
5. Crimp the opposite end of the b utt-splice connector to the wire connected
to ignition signal source.
6. Connect 1/ 4" female spade connector used in step # 3 above to terminal
# 4 on the back of the tachometer.
7. Connect a ground (-) wire to terminal # 3.
8. Connect a switched 12-volt power wire to terminal # 2.
9. Set switches for the appropriate number of cylinders


hope this helps.
 

andyv916

Member
Hey guys , I too have installed electronic ignition and a new SW rpm gauge , My gauge is not reading wrong but is acting sluggish slow to respond . I ordered the diode`s IN4005 from amazon and installed one silver band facing the gauge and it didnt get any better . I can live with it but it would be nice to have the gauge responding faster . any ideas ?
 
buy a new tach.----they have them that wrap around the coil wire and pick up the signal that way----I use them on are race car and my airplanes
 

sheep_mtn

Well-known member
GOLD Site Supporter
I typically run at 2000-2500 RPM, and today my stock analog tach went erratic on me (LMC 1500). It jumped to 5000 (pinned) and stayed there, then would drop to 3000-4000, and then sometimes would read correctly between 2000-2500. Repeat all of the above in any random order. Best place to start?
 

NDPilot

Active member
SUPER Site Supporter
I typically run at 2000-2500 RPM, and today my stock analog tach went erratic on me (LMC 1500). It jumped to 5000 (pinned) and stayed there, then would drop to 3000-4000, and then sometimes would read correctly between 2000-2500. Repeat all of the above in any random order. Best place to start?
I'm not familiar with the 1500 but if it's like my 1202 it is an electric driven analog. It sounds like a intermittent short or bad connection. That's where I would start looking.
 

sheep_mtn

Well-known member
GOLD Site Supporter
Thanks for the help. I had the panel apart recently and made sure the ground was secure to the machine, but didn’t check on the instrument side of the tach. Something may have come loose or shifted with me messing around in there.
 
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