My '04 STX did not come with a tach. The 4.6L engine uses coil packs on each cylinder, and some trims have the tach from the factory.

I am considering installing a VDO or AutoMeter tach gauge, but was wondering where I can pickup a signal wire from the factory wire harness.

The other option is to install a Tach Adapter module (AutoMeter p/n 9117), which requires cutting the +12v supply to the coil pack bus, which I already have identified (red/green wire in the black connector, by the ECU on the passenger side firewall). This adapter measures current draw on the supply line, every time any of the 8 coil packs are discharged, and turns this reading into a square wave which the analog tachs can pickup.

But I prefer to check first if there is an unused tach signal wire somewhere behind the dashboard (for those equipped with tachs) or are they using different wire looms in each trim?

Input please?

 

it really chaps me that ford quit putting tachs in the base xl and stx versions. The 04 STX's according to ford's own marketing literature are "Sporty".......so sporty in fact ford pulled a $20 tach. Go Figure what marketing genius thought that one up. good luck on retrofitting one and pls post the results.

 

Well, I found out that the "signal" wire found behind the instrument cluster carries many other triggers, and is a derivative of pin no. 5 found on the OBD2 diagnostics connector. The signals are multiplexed, thus cannot be deciphered by an analog tachometer that works with a square wave to function.

I've purchased and will install as described on my original post, the AutoMeter 9117 tach adapter module. This will feed the signal required by my analog tachometer (AutoMeter 2301).

The other obstacle is that most aftermarket tachs are big and bulky, and that there is no unconspicuous place to install on the dash.

My only resolution is to have a pillar-mount gauge pod on the driver's side, and this allowed me to also install a transmission temperature gauge, which is a benefit when towing.

Wiring should be straightforward and simple, and I will try to post a step-by-step documentation with pictures.

 

Success! I will post pictures ASAP.

 

The Autometer Tach Adapter (p/n 9117) wired into the ECU harness:



The Autometer Tachometer (p/n 2301) on the pillar/dash:

 

red04, nice job on the tach install. Did you consider the option of waiting and pulling the entire gage cluster from a wrecked 04 xlt? That's my first thought anyway. And hey, even if you work for AutoMeter it is a great post; it ought to generate interest as there are a number of people out there with an 03 stx or 04 xl/stx who sorely miss the tach. Altho i normally see merit in ford's marketing plans, no tach in an 04 stx is a crappy move. It gives the buyer the impression he is buying a low option truck as the gage face is noticeably plain. Do they really think the average STX buyer will not notice? Duh, they pitched the 04 STX directly at young males (and gals) who want a sporty truck. (i realize ford marketing is trying to create five "distinctive" 04 f150 models. And i know a little about ford plans to "decontent" the 04's) Anyway, once again great post and i think the install (with details of wiring hookup, wire routings, how the tach mounts to the dash ,etc ) would make a great "how to" worth posting on all the ford truck enthusiast sites. Also, in the previous post you mentioned a pillar mount gage pod that would include a tranny temp gage. Did you decide to only go with the tach or ?

 

Thanks for the compliments 03f150man.

I ended up changing the tach to a more sleek-looking AutoMeter 3708 Sport/Competition Series, 2 5/8" diameter, pedestal mount tachometer.



Reason being is that the 2301 as in the picture, was somewhat too big for my taste, after driving with it for a day.

It also turns out that even AutoMeter (the company) Support is not familiar with the 2004 F150 engines and ECU, and this is the very first one that was ever done on a vehicle like this. The wires (based on the ECU cable plug) as in the previous generation Fords were totally different.

Here is how the wiring came about...

1) Cut the RED/GREEN wire that you will find where it says connection made here on the picture below.

2) Then the following are the wiring pairs:

Adapter RED -> cut red/green wire near the big black plug.

Adapter RED/GREEN -> other cut red/green wire.

Adapter BLACK - ground

Adapter GRAY -> Tachometer Green Wire (through the cable tray).

I will try to post more pictures in a short while...

 

The engine is a low-revving engine. You can use a tach with a 6,000 rpm face so you get a "fuller needle sweep."

I used industrial quality double-sided automotive tape to secure the tach's pedestal onto my dash. (I did not want to drill any holes).

The Tach Adapter 9117 runs about $95, and the 2301 runs about $59. The 3708 runs $109... all AutoMeter brand.

Wrap all your wires with black electrical tape to give it the factory look finish.

All your tach's switched power supply wires can be found underneath the steering column.

Mod at your own risk.

Enjoy!