Electrical Stock tach wont work plugged into msd6al box?

Smurfstang88

Member
Nov 11, 2019
7
1
13
18
Virginia
Alright so like the title states, im trying to get my stock tach working by simply splicing into the original tach wire that used to go to the negative side of the coil. So i did that and plugged it into the tach output on the msd box and the tach is reading but i know its way off.. the car idles really low id guess around 700rpms or so but it reads around 1500 and when i rev it, it goes over 6k. Im not sure if it has something to do with it being a 4cyl cluster and its now a carbed 5.0 swap? Is there some sort of tach calibration or do i need something like the msd tach adapter? If i need the adapter id rather just buy a aftermarket tach.. thanks guys!
 
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CHILL347

I could barely beat on it while driving.
Oct 27, 2019
24
20
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32
Beaumont, Ab
You don't tie your stock tach into the tach output on the box. That output is for aftermarket tachs and shift lights. You shouldn't do anything with the factory tach wiring when installing the MSD box.
 

Smurfstang88

Member
Nov 11, 2019
7
1
13
18
Virginia
You don't tie your stock tach into the tach output on the box. That output is for aftermarket tachs and shift lights. You shouldn't do anything with the factory tach wiring when installing the MSD box.
Well crap i did in fact already know this but I figured it was worth a shot to try... anyways so i would be good just getting a autometer tach and plugging it into that tach output on the box? Is that all?
 

CHILL347

I could barely beat on it while driving.
Oct 27, 2019
24
20
13
32
Beaumont, Ab
Well crap i did in fact already know this but I figured it was worth a shot to try... anyways so i would be good just getting a autometer tach and plugging it into that tach output on the box? Is that all?
If you choose to disable your factory tach then yes. I use my factory tach even tho it isn't the most accurate, I have a shift light plugged into my MSD box that I rely on when shifting at the track and I just use my factory tach as a rough estimate as to where I am with RPM. But you could install an aftermarket tach if you'd like which they usually have a built in shift light. Me personally I just hate the big ugly aftermarket tach look inside the car. The small shift light is much cleaner looking. Personal preference.
 

Smurfstang88

Member
Nov 11, 2019
7
1
13
18
Virginia
If you choose to disable your factory tach then yes. I use my factory tach even tho it isn't the most accurate, I have a shift light plugged into my MSD box that I rely on when shifting at the track and I just use my factory tach as a rough estimate as to where I am with RPM. But you could install an aftermarket tach if you'd like which they usually have a built in shift light. Me personally I just hate the big ugly aftermarket tach look inside the car. The small shift light is much cleaner looking. Personal preference.
Alright i see what you mean although my tac is WAY off so im probably going to need to just get one of those ugly tachs. Do you know why the tac is so off? Is it because i would need an adapter or is it because its a 4cyl cluster? Im pretty much just curious for future reference if these tachs are interchangeable or not..
 

CHILL347

I could barely beat on it while driving.
Oct 27, 2019
24
20
13
32
Beaumont, Ab
Alright i see what you mean although my tac is WAY off so im probably going to need to just get one of those ugly tachs. Do you know why the tac is so off? Is it because i would need an adapter or is it because its a 4cyl cluster? Im pretty much just curious for future reference if these tachs are interchangeable or not..
I don't know why yours is way off other than it's wired wrong. You could start there. I believe aftermarket shift lights and tachs have an adjustable setting on them depending on how many cylinders you have. As far as the factory tach goes it may be a built in setting. Somebody on here must know for sure.
 

2000xp8

SN Certified Technician
Aug 8, 2003
6,650
888
194
NJ
The stock tach doesn't necessarily have to be dead on for you to know when to shift.
As long as it's consistent, it should be good.
If you know the car and know how it feels, you will adjust to reading the tach.
One could even argue that once you know the car you don't really even need to look at it.
I wouldn't waste my money on another tach.
 

Smurfstang88

Member
Nov 11, 2019
7
1
13
18
Virginia
The stock tach doesn't necessarily have to be dead on for you to know when to shift.
As long as it's consistent, it should be good.
If you know the car and know how it feels, you will adjust to reading the tach.
One could even argue that once you know the car you don't really even need to look at it.
I wouldn't waste my money on another tach.
Agreed here, since i bought the car the tach hasnt worked and have just driven by feel, no speedo no tach maybe I’ll take your advice
 

2000xp8

SN Certified Technician
Aug 8, 2003
6,650
888
194
NJ
Just to be clear, I think the speedo and tach should work.
I'm just not so worried about the tach being dead on.
 

Gs87GT

Active Member
Sep 25, 2019
81
28
28
Penn's Woods
Change the tach wiring back to stock configuration and see how it reads then? Just a thought.

Maybe try to find a tach or cluster for a 5L car of similar vintage and try that?

Just a thought....maybe you've already tried these suggestions. It would irritate me also having a tach that does not read correctly.