Hi all, I just had a tach from a '76 Corvette checked out and refaced to match the 1970 style of my car. Now that it's all hooked up, the tach is reading zero while the car is running. It jumps to 1000 RPM or so at first, and then comes right back to zero.

I have a new MSD setup and am using the tachometer out on the 6AL box. I ran a test light from the tach output and it is definitely outputting signal. I have the tach grounded to the birdcage, and power coming from the fuse box. Should I have the power or grounds somewhere else?

Thanks all for any advice - I'm taking advantage of some holiday time off to get my car going again.

 

Mine does that in the firebird when I went HEI........Never got around to repairing it. Be interesting to find the fix......................

 

You're problem is simple, but gonna cost a few more bucks. Most factory tachs don't accept MSD ignition tach outputs, and gonna need an adapter. Although a while back, had to use MSD adapter #MSD MSD-8920 on a build I did. This should solve things.

 

With an MSD ignigtion box, you may need one of the MSD adapters. Look through MSD's website. There is a list of different tachometers that need an adapter and those that don't. I don't think Chevy products need one but I think you have to do something if I remember correctly.

 

I have a '76 with an MSD Pro Billet distributor and 6A box and the tach works fine. Now when I got the car the tach did not work so I bought a new circuit board only to find out that you need to buy the ones from Zip, Corvette Central or Rik's vette that state they are "Calibrated" No problems here and I've had this set up for close to 2 years now. I used the original tach wire from the HEI distributor which I can only guess goes straight to the tach but there could be something in between that I haven't checked on or can see.

If you want to pay the shipping there and back I have a spare Autometer (Autogage) 5" tach you can try to verify there isn't a problem with the MSD box. I used it until I replaced the circuit board in my factory tach.

Eric


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Thanks for the replies. I hate to have to pull the dash apart again!! I'll walk away from it for a few days and come back to do it. Does it make sense that it goes to (and stays at) zero? I've heard when these fail they read all over the place.

 

Curious on this, as installed MSD boxes on a couple HEI ignitions, and the factory dizzy modules were always removed, leaving essentually no dizzy tach output. Is there something I'm missing here.

 

that's not true - it works just fine, you don't need the adapter! proof? I'll go ahead and post pictures of the MSD ignition running straight to my Tachometer.... I'm sure you're thinking a 70 tachometer - which I have no idea - however, his tach is a 76 tach...

rather than type, check out the Willcox video on Tach problems and solutions... it's comprehensive and it solved my problem I had the issues when I put the MSD on my car - but the problem was deeper seeded because the board, a replacement by the PO, was bad.

 

With my festive Xmas day green and red flame suit on, the easiest and most inexpensive way of avoiding this problem is not to install an MSD unit in the first place. I can't think of a bigger waste of money.........

 

Well, gotta agree with some here on a stock engine Mike, but on a built up engine with large lumpy idle cam, the multi spark ignition, helps smooth out the lumpy idle quite a bit. Believe Accel makes a replacement multi spark HEI module w/rev limiter built in, and probably the way I'd go now.

 

My box has a Tach wire output on one side of the box. A standalone metal spade, so all I needed was an extended wire with a female soldierless connector.

 

they've worked very well for me.... but then again, people swear by Fords - I only swear AT Fords

 

Mike, like most of us on this forum, we're just asking and offering help, not a poke in the eye.

John

 

Got it! Thanks for the help. I bought a tach from advance for $30~ and verified that I had a good signal. So as one last step before pulling the dash out again, I decided to try it one last time. I put the plug back on after bending the pins straight in case one was out of line. Plugged it back in, and, voila - working tach. Plug must have not been seated all the way before. Here's a video with the new dynomax vt mufflers in the background.

http://s116.beta.photobucket.com/use...bfe20.mp4.html

As soon as the tach started working, I was able to fix the turn signals (new flasher) and taillights (bulbs not seated properly). So, all in all, a good night working on the car. And after a long weekend getting the dash together and the horn to stop blowing (junk reproduction horn assembly had to be taken apart and washers added to keep it from going off so easily), I'm glad some things are starting to work the way they're supposed to!

Many thanks to Roger Scott of Corvette instrument service for the excellent work and turnaround time. So I went from having to pull the dash to replace the tach and steering column to replace the switch to car that operates like it should. Even the headlights go up and down, just a little slowly. I think a new relay will solve that.

btw, thanks Palmbeachvette on your offer, I wanted to take care of this while I'm off from work. If I had more time I would have taken you up on it, that was very generous.

 

Your welcome on the offer, just wanted to help a fellow vette owner in the Sunshine State. Glad to hear you got it figured out and it sounds really good.