NewZed Posted August 8, 2012 Share Posted August 8, 2012 The font used for the numbers on the face changed over the years. Someone might recognize the year if you showed a picture of the front. Just for fun. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 8, 2012 Author Share Posted August 8, 2012 The font used for the numbers on the face changed over the years. Someone might recognize the year if you showed a picture of the front. Just for fun. Word Quote Link to comment Share on other sites More sharing options...
Leon Posted August 8, 2012 Share Posted August 8, 2012 (edited) Not only the font, but the redline as well. 8/73 is right at the end of 240Z manufacturing. The 260Z received a 3-wire tach as part of the change-over to electronic ignition. Some very late 240Z's might have gotten 3-wire tachs as well. I remember this being discussed on classiczcars before. Edited August 8, 2012 by Leon Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 8, 2012 Author Share Posted August 8, 2012 Quote Link to comment Share on other sites More sharing options...
Leon Posted August 8, 2012 Share Posted August 8, 2012 (edited) You have either an early 260Z or possibly a late 240Z 3-wire tach. Should be easy to make it work (one connection to coil negative, plus power and ground). EDIT: follow beerman's post. Edited August 8, 2012 by Leon Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 8, 2012 Author Share Posted August 8, 2012 You have either an early 260Z or possibly a late 240Z 3-wire tach. Should be easy to make it work (one connection to coil negative, plus power and ground). EDIT: follow beerman's post. Cant wait to leave work now!!!!!lol Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 9, 2012 Author Share Posted August 9, 2012 Well after a few hours of checking wiring from the stock harness, switching out the 240 and 280 tach's, I finally got the 280z tach to work. I ran jumper wires to the +12v and a ground to the back of the tach, got my signal wire from the negative side of the coil, and the MOST important thing is to make sure that the mounting post are grounded as well, as soon as I did this the tach worked, even though it jumped around a bit, but I can put in a resistor on the signal wire for that. Thanks for all the knowledge who replied to this post. Oh yeah, the 280Z tach had the same hook-up that the 240z tach did, wiring harness was different though. Quote Link to comment Share on other sites More sharing options...
beermanpete Posted August 9, 2012 Share Posted August 9, 2012 Cool. Glad you got it to work. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 10, 2012 Author Share Posted August 10, 2012 Spoke too soon, not working now. I got a working gauge in the mail, the 40 year old wiring must be frying my tach. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 16, 2012 Author Share Posted August 16, 2012 Im gonna try a 4 wire guage, and run all new wiring. Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 16, 2012 Share Posted August 16, 2012 I don't know exactly what "does not work" means in your case, but I had a tach that stopped working after I did some ignition work (swapped my 1978 Z coil for a Z31 coil). The needle would just dance around at ~1000 RPM, obviously getting some impulses from the coil but not able to use them. I attached a condenser/capacitor to the negative post of the coil on the theory that I had some electrical noise on the blue wire to the tach. It fixed the problem, tach works perfectly and has for ~6-8 months, but I couldn't go very deep in to why. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 16, 2012 Author Share Posted August 16, 2012 That's part of fun though, Working on old cars Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 17, 2012 Author Share Posted August 17, 2012 I don't know exactly what "does not work" means in your case, but I had a tach that stopped working after I did some ignition work (swapped my 1978 Z coil for a Z31 coil). The needle would just dance around at ~1000 RPM, obviously getting some impulses from the coil but not able to use them. I attached a condenser/capacitor to the negative post of the coil on the theory that I had some electrical noise on the blue wire to the tach. It fixed the problem, tach works perfectly and has for ~6-8 months, but I couldn't go very deep in to why. Where did you get that condenser? Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 23, 2012 Author Share Posted August 23, 2012 Anyone know what condensor and where to buy it ? Goes on the signal wire to adjust the signal Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 23, 2012 Share Posted August 23, 2012 It was the typical condenser used up by the coil. I think that it was 0.5 microfarads, if I remember and read my meter right (500 nanofarads). An alternator condenser would probably serve the same function (I just measured one recently and it was 0.7 mF), available at most auto parts stores. It's backyard electronics engineering though, I don't really know what I was doing. But I don't think it can hurt. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 23, 2012 Author Share Posted August 23, 2012 It was the typical condenser used up by the coil. I think that it was 0.5 microfarads, if I remember and read my meter right (500 nanofarads). An alternator condenser would probably serve the same function (I just measured one recently and it was 0.7 mF), available at most auto parts stores. It's backyard electronics engineering though, I don't really know what I was doing. But I don't think it can hurt. My coil has a condenser on the positive side that is mounted to the coil bracket, I was told this was for noise reduction in the car speakers Quote Link to comment Share on other sites More sharing options...
NewZed Posted August 23, 2012 Share Posted August 23, 2012 I can't say for sure but the word "noise" may have originally been meant to refer to electrical noise and been layman termed down to mean noise though the radio speakers. A side effect of electrical noise. Electrical "noise" tends to cause problems for sensitive devices. Anyway, I just put it out there as an option. I've also read of using a diode on the tach circuit for a similar purpose, to condition the signal to the tach. There's probably someone out here who knows much more about electronics and electrical theory who could help, if you posted a video or gave really good description of what the tach is doing. You said "not working" in #29 but didn't give any more details. If the needle is twitching, there's something there, you just have to find a way to use the good part of the signal and get rid of the rest. Quote Link to comment Share on other sites More sharing options...
Zmanco Posted August 23, 2012 Share Posted August 23, 2012 I used to run a Pertronix on my 73 with the stock tach with no issues. It has been a long time now, but I think Beermanpete's instructions should work. You do have to make sure you get the 2 BW wires connected properly otherwise as he says, the car will run, but the tach won't work. If you're going to replace your tach anyway, I'd recommend you switch to a later 3 wire. They are easier to find, and you can swap the internals to keep the stock faceplate and needle. After buying 2 used 4 wire tachs that had issues, I swapped to a 3 wire and haven't had to touch it since. Quote Link to comment Share on other sites More sharing options...
daddydonuts Posted August 24, 2012 Author Share Posted August 24, 2012 Link on youtube to my tachometer guts from the 280Z working, power and ground hooked up directly to the battery and tach signal hooked up to the negative side of coil. When I put the guts back into either the 240 or 280 tachometer, I cannot get the tachometer to work.It has to be a ground issue???? Quote Link to comment Share on other sites More sharing options...
Zmanco Posted August 24, 2012 Share Posted August 24, 2012 Reading your post reminds me that I think the polarity of the two posts are reversed for the 3 wire vs. the 4 wire? Take a closer look to see if that's the issue. Quote Link to comment Share on other sites More sharing options...
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