Tach connection - v8 Miata Forum - Home of the v8 Miata Conversion

V8 Miata Wiring, Electrical, and ECUs v8 conversions on a Miata can be tricky. Post your comments or questions within with regards to swap wiring and electrical.

Tach connection

Reply

 
 
 
Old 08-21-2018, 06:24 PM
  #1  
V8 Miata Fan
Thread Starter
 
Join Date: Oct 2017
Location: PNW
Posts: 54
Thanked 2 Times in 2 Posts
Default Tach connection

5.0 build using a FiTech efi system so I no longer have the ford ecu...

I understand the tach wire is yellow/blu at the cluster and also in the diagnostics box. Can I jumper off either of those points straight to the negative side of the coil ?

Is a resistor required ?

Thanks in advance
hotwheels000 is offline  
Reply With Quote
Old 09-06-2018, 12:50 AM
  #2  
V8 Miata Fan
 
engineer's Avatar
 
Join Date: Aug 2015
Location: Sydney Australia
Posts: 80
Thanked 4 Times in 4 Posts
Default

Hi,

use the Dakota digital universal tach adapter us ethe fti as the trigger and the Dakota to drive the tacho in the dash. It does the 8 to 4 cyl conversion for you.

It saves a lot of mucking around.

cheers
engineer is offline  
Reply With Quote
Old 10-11-2018, 10:45 AM
  #3  
V8 Miata Fan
Thread Starter
 
Join Date: Oct 2017
Location: PNW
Posts: 54
Thanked 2 Times in 2 Posts
Default

Ok, I should have mentioned this is a 1992 NA...

Dakota Digital SGI 8E tach adaptor installed. Power and grounds to unit are fine, the unit flashes the red dot dot like it is receiving signal no matter what configuration output I use. Tach signal in is being pulled of the neg side of the coil. The problem is my dash tach is non responsive. Tach worked flawless before the swap.

I have tried all the output options offered, high out, normal out, and a jumper between high and not used terminal. I am using the screw on the back of the cluster that goes to the tach as a connection point versus splicing into the wire. Continuity between that screw and the wire is fine so I am assuming that is ok to do.

2 calls to DD and I don't seem to be getting anywhere. I check the high output and it is putting out 14.39v dc, low is putting out 534mv dc (that seems wrong) I did get a 5.6v dc reading one time on the low side. Seems to me I need to be using the high output anyways.

Any insight ????????

Last edited by hotwheels000; 10-11-2018 at 10:49 PM.
hotwheels000 is offline  
Reply With Quote
Old 10-24-2018, 09:18 AM
  #4  
V8 Miata Fan
 
engineer's Avatar
 
Join Date: Aug 2015
Location: Sydney Australia
Posts: 80
Thanked 4 Times in 4 Posts
Default

Hi,
Make sure that you are sending the output from the DD Tach Adpater to the correct wire at the cluster.

Wiring plugs at the back of the Mazda instrument cluster can be found as follows. Plug 1 is white, plug 2 is black, and plug 3 on 99-05 cars is small white. The tach wire is as follows:

90-93: 12v is 2K black/yellow, tach is 1H yellow/blue.
94-97: 12v is 2K black/yellow, tach is 1H black/white.
99-05: 12v is 1C black/yellow, tach is 2K green/orange.

Check to make sure that you signal output from DD is going to the correct wire in the cluster as per above.

If it is and its still not working then a pull up resister may be required.

Below is an exert from Flyin Miata on how to set up a pull up resistor into the tacho signal wire, although this is for a GM ECU it illustrates the point:


Tachometer mod. The Miata tachometer is expecting a different voltage input than the GM ecu puts out, so we need to fool it. A 2200 ohm (2.2K) resistor needs to be jumpered in between switched 12 volts (Mazda 12v wire listed below) and the tachometer input lead (white wire in GM bulkhead connector) going from the GM harness to the Mazda instrument cluster.

The white GM wire will connect to the Mazda tach wire going in to your instrument cluster (below). The 12v -> 2200 ohm resistor -> will “T” into this tach wire. An easy way to visualize it is to just think of the 2200 ohm resistor as a jumper wire between the 12v wire and the tach wire where it plugs into the instrument cluster. Make sure you cover the resistor with heat shrink tubing to protect it from shorting! What you’re doing here is “pulling up” the tach signal voltage so the Mazda tach can read it.
engineer is offline  
Reply With Quote
Old 10-24-2018, 10:00 AM
  #5  
V8 Miata Fan
Thread Starter
 
Join Date: Oct 2017
Location: PNW
Posts: 54
Thanked 2 Times in 2 Posts
Default

Thank you for the additional info.

For the 92 model I had it hooked up as described less the pull up resistor. As a quick verification I bought a cheap tach and used it instead of the stock one. DD still would not send a signal to the cheap tach. Hooked the cheap tach up directly bypassing the DD box used its 4/6/8 cylinder selector switch and it worked perfect. I took it one step further and hooked up the factory tach bypassing the DD and as expected I saw double the RPM readings.

From all the above findings I came to the conclusion that the DD was defective from the factory. Summit is sending me a new one, I will update the post when it arrives with my findings.

Thanks again for your help
hotwheels000 is offline  
Reply With Quote
Old 10-24-2018, 06:28 PM
  #6  
V8 Miata Fan
 
engineer's Avatar
 
Join Date: Aug 2015
Location: Sydney Australia
Posts: 80
Thanked 4 Times in 4 Posts
Default

Ahhh OK...that would explain it...its a bit hard to get things working when you are using a defective device to begin with

Great to hear that Summit are sending you a new one.

The DD unit is pretty awesome....when it is a working model

keep us posted..

cheers
engineer is offline  
Reply With Quote
 
 
 
Related Topics
Thread
Thread Starter
Forum
Replies
Last Post
Gunpilot
V8 Miata Drivetrains
7
08-30-2015 06:14 PM
Hammerhead1445
V8 Miata Wiring, Electrical, and ECUs
2
09-01-2012 08:51 PM
Carlisle
V8 Miata Wiring, Electrical, and ECUs
3
04-23-2012 12:01 PM
konman
V8 Miata Wiring, Electrical, and ECUs
4
09-23-2011 04:36 PM

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 

Thread Tools
Search this Thread
Rate This Thread
Rate This Thread:
You have already rated this thread Rating: Thread Rating: 0 votes,  average.

Quick Reply: Tach connection


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.