When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Can anyone identify this electronic tachometer. It`s out of my 74. I need wiring diagram for the connection on back of tach. and any information about calibration. Or where I can look it up. Thanks The back. I believe this is the sending unit ? It is under the dash These connect to the back of the tach.
I am redoing the interior of my 74 and while I have it all apart (again) I thought I would try and get the tach working correctly. right now it works but reads 1500 RPM`s high. Looked up the part # on the back and found on ebay and Ecklers I can get the circuit board already calibrated. What I called the sending unit in the photo must actually be the circuit board. I guess I will have to cut the wrap around it to see. Is this normal, the circuit board out side of the tach. I just want it to work.
lastcaveman
Here. Read this. Electric tachs were on 75-77s from all I can find. It will help you with setting up your tach. You want to read this below because different years had slightly different zero'ing setups.
The circuit board is inside the tach housing. You are just seeing the terminals to connect the leads. http://www.corvettefaq.com/c3/RebuildSpeedo.htm
Gimme a few minutes and I'll go take a picture of my spare (old) circuit board (I should be able to find it). It used to be on forum until the photobucket screwup messed up a bunch of pictures...... gimme a few minutes.
Last edited by carriljc; Feb 22, 2020 at 06:51 PM.
I am redoing the interior of my 74 and while I have it all apart (again) I thought I would try and get the tach working correctly. right now it works but reads 1500 RPM`s high. Looked up the part # on the back and found on ebay and Ecklers I can get the circuit board already calibrated. What I called the sending unit in the photo must actually be the circuit board. I guess I will have to cut the wrap around it to see. Is this normal, the circuit board out side of the tach. I just want it to work.
OP
? Does yours have an HEI distributor with coil inside big cap ?
? Is your C3 made in Late 1974 production ?
I recall passing thru your neck of the woods, late at night in Fall 2013 ... lotsa backroads with letter / double letter designations ... then near springfield, picked up US60 East toward Van Buren & Big Spring NP.
lastcaveman
Here you go. in case you can't see from upper left to upper right and then below in this order:
12V
GND
COIL
tachometer circuit board / tach ckt board pictures
Last edited by carriljc; Feb 22, 2020 at 06:15 PM.
lastcaveman Hmmm... the more I look at your connectors and the funnier they look. You might have to pull your tach out of the housing to eyeball any labels on your circuit board. It struck me as odd that you had lug terminals since I had never seen those.
lastcaveman well, upon further review, it looks like the lugs are MISSING from your circuit board. The 3 blade lugs should come out throught the slots on the right hand side of this picture. Looks like someone is using screws instead. You'll have to turn the circuit board over to determine which line traces to which terminal.
Once you figure out where to connect them, then you can test the tach before putting the dash back together..... if it works ok, otherwise just get a new tach board. Remember to read the zeroing method for the year of your tach(unless your new board has other instructions): http://www.corvettefaq.com/c3/RebuildSpeedo.htm
Last edited by carriljc; Feb 22, 2020 at 06:12 PM.
OP
? Does yours have an HEI distributor with coil inside big cap ?
? Is your C3 made in Late 1974 production ?
I recall passing thru your neck of the woods, late at night in Fall 2013 ... lotsa backroads with letter / double letter designations ... then near springfield, picked up US60 East toward Van Buren & Big Spring NP.
lastcaveman well, upon further review, it looks like the lugs are MISSING from your circuit board. The 3 blade lugs should come out throught the slots on the right hand side of this picture. Looks like someone is using screws instead. You'll have to turn the circuit board over to determine which line traces to which terminal.
Once you figure out where to connect them, then you can test the tach before putting the dash back together..... if it works ok, otherwise just get a new tach board. Remember to read the zeroing method for the year of your tach(unless your new board has other instructions): http://www.corvettefaq.com/c3/RebuildSpeedo.htm
I`m beginning to understand what is going on. I opened the shrink wrap and found the circuit board. This is it in the picture I dont know why it was done this way maybe they didn`t have the connector or what. But the wires from the distributor are soldered to the board at the connector blades and then the three wires red, black and white areat the nuts then those wires run to the back of the tach. I will order a new board and wire with the plug. If I can figure out the right board. I guess it would be the 75/77 one. Oh yeah, I cut the red wire. lol
Last edited by lastcaveman; Feb 22, 2020 at 08:00 PM.
lastcaveman
well, i don't fault anybody for doing what they have to do, but that sure looks like a lot of work. That is still some crappy work.... I didn't have the connector but I have had blade connectors installed for years (heat-shrink wrapped and insulated).
I don't know what you mean by "shrink wrap". Go look at the willcox website....new ones available and it's cheaper than mine was locally ~15 years ago. Looks like it's all super whammerdyne updated wonderful thing.
There is a video in the link too!!
Make sure you have a Tach Filter or make one (2 - 3 bucks if you know how to solder and use heat shrink). I actually had to remove my tach filter since my tach signal now comes from my MSD-6 box....when I had the tach filter in place, and the signal being fed from the msd box, it would start jumping around at about 3500 rpm-- removed tach filter and it is smooth. If you need the schematics for the tach filter just say so and I'll go look for it....or you can use the search function of the forum.
Last edited by carriljc; Feb 22, 2020 at 08:35 PM.
I was looking at your pictures again....if you break open that "blob" that was under the dash it looks like it may be the connector to the back of the tach???
I was looking at your pictures again....if you break open that "blob" that was under the dash it looks like it may be the connector to the back of the tach???
Here it is. The blob is just to the right of the circuit board. It looks like a very large shrink tube, I cut it open with scissors .
Not yet. I `m going to call Wilcox tomorrow. Right now the tach sets at about 2 or 3 thousand rpm`s. When voltage is applied it go`s to 0 but at 70mph it reads around 1500 higher than it should. I checked this with a timing light as well as another tachometer. Now that I have found the circuit board and it has a pot. my question is If I adjust the pot to where the rpm`s are right will the needle need to be re-set to 0 ?
Not yet. I `m going to call Wilcox tomorrow. Right now the tach sets at about 2 or 3 thousand rpm`s. When voltage is applied it go`s to 0 but at 70mph it reads around 1500 higher than it should. I checked this with a timing light as well as another tachometer. Now that I have found the circuit board and it has a pot. my question is If I adjust the pot to where the rpm`s are right will the needle need to be re-set to 0 ?
Answer is no.... you do a zero set by removing the needle and powering up the tach board and re-installing the needle.
Then you dial the board in.
You've got an old Nord board which was pretty much a disaster waiting to happen. Look at the size of the cap on top the board... and how it's fixed to it and it has a one turn pot for adjustment which if you have this on a calibration machine you can flick it and the RPMS will change....
The board is to be powered up, zero set then input rpms are added (you can do this by using another source for your RPM's such as an old style dwell meter). I'm not sure if the Nords tach board can read both square and wave signals so you may have to run it through the filter first. Our boards can read either.
I don't know if you have done so or not but my suggestion is to purchase a newer USA made board.
Information about this Tachometer
