Factory Tach with MSD?

[broncoman6524]

I tried to put a factory tach into my truck last night, I wired it up correctly. I know there is power because when you turn the key the needle will got from straight down and "go around" (full sweep) to right back where it started.

If you start the truck the needle just moves faster.

Any suggestions? It's hooked up on the side of the box where it's supposed to be when you eliminate the Stock HEI parts.

Thanks

 

[Smitty]

Check out the MSD web site. They have solutions for common problems and tach compatibility is one of the common problems.

 

[nvrenuf]

On the factory tach harness there is a resistor inline in the wire going to the tach signal on the MSD box. Check the MSD wiring diagram first but I believe that needs to be removed.

 

[broncoman6524]

There is no wiring harness...I took the cluster out of a truck, forgot the harness. I just made my own 12v, ground, and coil wire.

 

[nvrenuf]

...12v, ground, and coil wire.

That may be your problem, iirc the original harness is 12v, tach plug on MSD & coil. I don't remember the OE harness using a ground wire.

 

[broncoman6524]

alright, I'll check that out. Only reason it's there is because there is a plug for it that says "Ground"

 

[clstolten]

broncoman
I have a similar problem with the factory tach I put in my 74 with tbi. It zeros out when power is applied but when I start the truck the needle just flutters around. I also hooked mine up to 12v, ground and coil. I only used the factory plug, and built the rest of the harness myself. I will be interested to see if you find a solution.

 

[chulisohombre]

I tried to put a factory tach into my truck last night, I wired it up correctly. I know there is power because when you turn the key the needle will got from straight down and "go around" (full sweep) to right back where it started.

If you start the truck the needle just moves faster.

Any suggestions? It's hooked up on the side of the box where it's supposed to be when you eliminate the Stock HEI parts.

Thanks

i have aftermarket sunpro tach,but i thought they all worked the same.i plugged mine in with a direct wire from the msd to the tach and its fine.when i had it hooked into the coil,that is when it went irratic and didnt get a good signal.i wired it in the way it says to on the msd site.i originally had point ig when i got the truck

 

[Smitty]

http://www.msdignition.com/

 

[broncoman6524]

Not trying to be a D*ck...but like I said, I wired it up per MSD directions from the packet. And the it is the exact way that I did it in my blazer, except that it was a sunpro tach.

I was more of going in a direction of if it needed a resistor or something, or a way to test the actual tach.

I'm goin to go ahead and assume that it is bad.

 

[Smitty]

Not trying to be a D*ck...but like I said, I wired it up per MSD directions from the packet. And the it is the exact way that I did it in my blazer, except that it was a sunpro tach.

I was more of going in a direction of if it needed a resistor or something, or a way to test the actual tach.

I'm goin to go ahead and assume that it is bad.

If you bother to go on the MSD site and present your situation in the forum, you might just be able to solve your problem... Not trying to state the obvious, but sometimes it's best to go to the manufacturer of the product for the answers. I'm running three of the MSD systems and I can tell you that all of the answers are not in that little installation manual that comes with the unit.

 

[chulisohombre]

If you bother to go on the MSD site and present your situation in the forum, you might just be able to solve your problem... Not trying to state the obvious, but sometimes it's best to go to the manufacturer of the product for the answers. I'm running three of the MSD systems and I can tell you that all of the answers are not in that little installation manual that comes with the unit.

x2.maybe the forum there can tell you more or call msd for some tech answers.if the tach doesnt have a good ground it will jump all over the place also.i put my ground from the tach to the dash board.maybe that would help.there should be no resister to stop the needle from bouncing.the signal should be calculated inside the msd box and then sent out of the box via the tach hookup on the msd itself.the signal coming from the coil will not give you a true signal because of the multiple spark it is giving off.

 

[broncoman6524]

I took your advice and posted on their forum...

To be honest I think that the tach is bad, I have MSD in my DD and HAD a tach wired the same way. It used to work until one day while I was driving it just stopped...Couple days later It worked again until recently it stopped and has been dead since.

Weird...

 

[chulisohombre]

I took your advice and posted on their forum...

To be honest I think that the tach is bad, I have MSD in my DD and HAD a tach wired the same way. It used to work until one day while I was driving it just stopped...Couple days later It worked again until recently it stopped and has been dead since.

Weird...

maybe it is time for a new tach then.i dono.good luck.if you checked the wiring and all the connections are good,then it could be a dead tach.

 

[RootBreaker]

I may have missed it but what year truck do you have?

I put a 79 factory gmc tach setup in my 78 chevy....

it works fine.. then put a msd ignition on.... all I had to do was take the wire off of the distributor (on tach) and go to the msd, -6al in my case, and it works......


if you think the tach is bad.... try finding a truck to hook it up to...

I believe there are 3 wires.... 12v, ground and tach wire.......

 

[chulisohombre]

I may have missed it but what year truck do you have?

I put a 79 factory gmc tach setup in my 78 chevy....

it works fine.. then put a msd ignition on.... all I had to do was take the wire off of the distributor (on tach) and go to the msd, -6al in my case, and it works......


if you think the tach is bad.... try finding a truck to hook it up to...

I believe there are 3 wires.... 12v, ground and tach wire.......

mine has 4.12v,ground,tach lead and backlight wire to light switch power supply

 

[RootBreaker]

mine has 4.12v,ground,tach lead and backlight wire to light switch power supply

hmmm interesting... guess I dont know then...

I just put my hot into my fuse panel on ignition, another on ground then the last on the msd box....

so what supplies the 4.12v then?
you should be able to keep that hooked up but take the tach lead off and run that to the msd.....

 

[chulisohombre]

hmmm interesting... guess I dont know then...

I just put my hot into my fuse panel on ignition, another on ground then the last on the msd box....

so what supplies the 4.12v then?
you should be able to keep that hooked up but take the tach lead off and run that to the msd.....

that would work if it doesnt have a internal light.he said this is stock i guess,so it should im guessing only have 3 wires anyway and be backlit by the dash lights themselves.my 4th wire was white and hooked to the dash light power supply so that you could also dim the tach if wanted.12v.the only way to get a good signal to the tach is to hook it directly to the msd box.there would be too many sparks at once for the tach to handle it off the coil.needle would be reallly jumpy.

 

[broncoman6524]

It is a factory tach, It came from a 70's truck, but was spliced in. I have no idea if it ever worked.

Like root-breaker said, I hooked mine to both the box and dizzy and nothing happened either time. Guess I'll have to find another one.

 

[chulisohombre]

It is a factory tach, It came from a 70's truck, but was spliced in. I have no idea if it ever worked.

Like root-breaker said, I hooked mine to both the box and dizzy and nothing happened either time. Guess I'll have to find another one.

either the tach or the msd.you said the msd was new i believe.this leads me to think if you hooked it up correct that the tach is the culprit