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I could be wrong but I am leaning towards no.
 

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sables had tachs look for one from a sable or an lx
 

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Discussion Starter · #9 ·
awesome! I just want a tach. This is the first car ever that I dont have tach and it sucks
 

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The 1990-1995 models are plug and play...however I remember the 86-89 models are not. A couple of people tried swapping them in with no success. I have a feeling that cars, unless they came with a factory tach, are missing the signal wire off of the TFI module harness. Or maybe there is some other wire/connection missing. I'm going to the yard tmrw...well I guess in a few hours since it's 1AM :lol: so I will pull an 89 SHO dash apart and a 86-89 dash and compare. I am curious about this as well for my 87 since it has just a speedometer.

ignore the missing wire explanation, see Jeff Ks post below.
 

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Discussion Starter · #11 ·
The 1990-1995 models are plug and play...however I remember the 86-89 models are not. A couple of people tried swapping them in with no success. I have a feeling that cars, unless they came with a factory tach, are missing the signal wire off of the TFI module harness. Or maybe there is some other wire/connection missing. I'm going to the yard tmrw...well I guess in a few hours since it's 1AM :lol: so I will pull an 89 SHO dash apart and a 86-89 dash and compare. I am curious about this as well for my 87 since it has just a speedometer.
oh :( well good thing you called that. Better than me going out and buying a cluster, just to be in utter disappointment :)
 

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Tach signal in EEC IV distributor engines comes off the IDM (ignition diagnostic monitor) circuit. The IDM circuit has a 22K ohm resistor in it somewhere in the harness. Shouldnt be too hard to tap into the IDM circuit (on the PCM side of the 22K resistor) and feed that to the cluster for the tach. Or, run a seperate wire, with an inline 22K resistor, directly from the coil neg terminal (which is the origin of the IDM circuit) to the tach in the cluster. Some VERY early EEC IV Fords didnt have IDM, but I am pretty sure that all Taurus / Sable have the IDM circuit to the PCM.
 

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Tach signal in EEC IV distributor engines comes off the IDM (ignition diagnostic monitor) circuit. The IDM circuit has a 22K ohm resistor in it somewhere in the harness. Shouldnt be too hard to tap into the IDM circuit (on the PCM side of the 22K resistor) and feed that to the cluster for the tach. Or, run a seperate wire, with an inline 22K resistor, directly from the coil neg terminal (which is the origin of the IDM circuit) to the tach in the cluster. Some VERY early EEC IV Fords didnt have IDM, but I am pretty sure that all Taurus / Sable have the IDM circuit to the PCM.
Oh it comes off of there? Woops I'll edit my post.

So you would need to run a wire from the PCM, wire in a 22k ohm resistor, run the wire down to the negative terminal on the ignition coil harness, then run a wire from there into the cabin? I'll have to poke around under the hood tomorrow to see if the wire is actually there.
 

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Look at the coil neg terminal. It should have 2 wires going to it. Memory (which could be wrong!) tells me they both are a green / red stripe wire. One on those wires goes to the TFI (the TFI grounds / ungrounds this wire to fire the coil) and the other one goes into the harness to the PCM. This is the IDM circuit, that has a 22K resistor somewhere in it, that goes to the PCM. PCM uses this circuit to see if the TFI is actually firing the coil. If TFI isnt firing the coil PCM will set a code 18. If you find the IDM circuit at the PCM, you can just tap into the IDM wire and run it to the tach. I have 86 wiring diagrams around somewhere and could find the PCM pinouts for you if you dont have that info available. 87 should be the same as 86.

If you dont want to do that, you could run a wire from the negative coil terminal, to a 22K ohm resistor, into the cabin, and to the tach. That is pretty much how we used to wire tachs back in the "old days" before electronic ignitions / computer controls, etc. Run a wire (no 22K resistor) from coil neg terminal to the tach input.

I dont fully understand the function of the 22K resistor in the EEC IV system, but I think it is a current limiting protection for the PCM to avoid frying the PCM inputs.
 

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Why not just pull the dash harness from a car with a tach and do it that way?

I was always afraid of pulling the dash, but it isn't that bad if you do it the right way.
 

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Look at the coil neg terminal. It should have 2 wires going to it. Memory (which could be wrong!) tells me they both are a green / red stripe wire. One on those wires goes to the TFI (the TFI grounds / ungrounds this wire to fire the coil) and the other one goes into the harness to the PCM. This is the IDM circuit, that has a 22K resistor somewhere in it, that goes to the PCM. PCM uses this circuit to see if the TFI is actually firing the coil. If TFI isnt firing the coil PCM will set a code 18. If you find the IDM circuit at the PCM, you can just tap into the IDM wire and run it to the tach. I have 86 wiring diagrams around somewhere and could find the PCM pinouts for you if you dont have that info available. 87 should be the same as 86.

If you dont want to do that, you could run a wire from the negative coil terminal, to a 22K ohm resistor, into the cabin, and to the tach. That is pretty much how we used to wire tachs back in the "old days" before electronic ignitions / computer controls, etc. Run a wire (no 22K resistor) from coil neg terminal to the tach input.

I dont fully understand the function of the 22K resistor in the EEC IV system, but I think it is a current limiting protection for the PCM to avoid frying the PCM inputs.
Yup I do have 2 wires coming off the harness for the coil negative terminal.

Sounds like I need to do some tracing on that line after thanksgiving. So that is what the IDM cirucit is, ok. That will be great if I have the wiring already intact. Hopefully that is the case! I have some wiring diagram booklet I got off of eBay for an 87, but it looks pretty weak.

And the backup solution doesn't sound bad either. I'm planning to wire in a digital instrument cluster I got from an 94 Sable w/a 90-91 dashboard. It'll be a fun project in 2011.
 

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If my explorations are correct, the wire for the tach is present in the cluster harness even if the tach is not. Might actually be plug and play.

At least this holds on the 88 I looked at.
 

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When I had my 91 L (base model) wagon, it originally had a non-tach cluster. I purchased a same-gen tach cluster, switched the speedo to preserve the odometer reading and installed the tach cluster. It worked perfectly. Plug-and-play.
 

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When I had my 91 L (base model) wagon, it originally had a non-tach cluster. I purchased a same-gen tach cluster, switched the speedo to preserve the odometer reading and installed the tach cluster. It worked perfectly. Plug-and-play.
Yea the 90 and up are plug and play. It's the 86-89 I had read many a time on here, being something that wouldn't work.

jw...that's cool if the 88 has it. maybe old posters are wrong...
 

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Ah ok, so I think I learned that the 86-89 L models may lack that wiring for a tachometer.

Today I scored a neat cluster from an 87 Sable dark blue GS Wagon. It was an extremely base model. Real blue vinyl split bench seats, no power seats, locks, or windows...but the instrument cluster was there! Decided to grab it :) Will do a test run to see how it works in coming weeks.

tonyroc14 if it ends up working, you can have dibs on it. I'm just using it until I do the digital instrument cluster conversion.

Interesting to note you can see the lighting for the "SHIFT" "LIFTGATE AJAR". There must be a variety of iterations of this cluster.
 
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