Electrical Stock tach wont work plugged into msd6al box?

Smurfstang88

Member
Nov 11, 2019
63
10
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!
 
  • Sponsors(?)


StangNet created a new car social app called knowmoto! Add your Mustang or post a photo in the knowmoto app and enter for a chance at a $100 gift card from LMR. Click the LMR Logo for more about the knowmoto Mega Thread!

CHILL347

I could barely beat on it while driving.
Oct 27, 2019
24
22
13
34
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
63
10
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
22
13
34
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.
 
  • Agree
  • Like
Reactions: 1 users

Smurfstang88

Member
Nov 11, 2019
63
10
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
22
13
34
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
7,173
1,208
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.
 
  • Agree
  • Clever
Reactions: 1 users

Smurfstang88

Member
Nov 11, 2019
63
10
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
7,173
1,208
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.
 

Gs1987GT

Active Member
Sep 25, 2019
289
89
38
MidAtlantic
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.
 

Smurfstang88

Member
Nov 11, 2019
63
10
18
Virginia
I have yet to try wiring it “stock” which is just to the negative side of the coil but i doubt it will work i will try that tomorrow and tell of my results for anyone wondering in the future.. as for the cluster for a 5L car no luck locating one yet so am about to the point of buying ugly external tach... thanks for your input
 

Blown88GT

Founding Member
Nov 13, 1999
2,172
518
164
Palm Beach Gardens, FL
I have yet to try wiring it “stock” which is just to the negative side of the coil but i doubt it will work ...
Why do you doubt it will work, when that is the way it was designed to work?
EVTM_p022.jpg

EVTM_p043.jpg
 

Smurfstang88

Member
Nov 11, 2019
63
10
18
Virginia
Why do you doubt it will work, when that is the way it was designed to work?
EVTM_p022.jpg

EVTM_p043.jpg
The reason i said i doubt it is because it sounds like the 4cyl tach was designed to only read properly with the 4cyl engine? As far as what ive gathered from this forum but then again i dont know for sure.. unless im misunderstanding something?

Id love to get the stock tach to work well enough though i may add, i have a very clean dash with no holes in it and would like to keep it that way.. will try wiring it up to stock specs in the morning.
 

Smurfstang88

Member
Nov 11, 2019
63
10
18
Virginia
Why do you doubt it will work, when that is the way it was designed to work?
EVTM_p022.jpg

EVTM_p043.jpg
UPDATE
So i tried stock wiring today and no surprise to me it did not work.. tach moves slightly when i turn the ignition on so its getting power, but does not read anything when engine is running.. im assuming either because its the 4cyl tach like mentioned or msd ignition aforementioned..

Edit: So looks like either I’ll be waiting to find a stoch v8 cluster, or possibly a external tach as it seems theres no other options unfortunately.
 

Smurfstang88

Member
Nov 11, 2019
63
10
18
Virginia
Yea thanks for the links but I mentioned before in the thread how those adapters being 55$ id rather just get a external tach or buy a v8 cluster considering mine tops at 6k.. im thinking of the glowshift shiftlight tach similar to autometers shift light with led tach.. maybe hide it in a ac vent.