It depends on why the tach is not working. If it is the actual gauge (which is just a stepper motor controlled by the cluster micro-controller) then you can swap the flexible circuit board from your old cluster into the new one and the accumulated mileage will go along with it.
However if it is an electronic problem with the stepper motor driver circuit then swapping the circuit board (which must be done for the engine to start--more about this below) will also move the problem to the new cluster.
Your '04 (and all '99 to '04 Mustangs) has the Securilock (PATS) type C system, in which the PATS module is integrated with the HEC (Hybrid Electronic Cluster) electronics and virtually "married" to the PCM via a shared security ID (SID) programmed at the factory. This is why you cannot just swap instrument cluster assemblies.
There are two workarounds. One is to have Ford dealer with the required IDS (Integrated Diagnostic System) module "marry" the new cluster and PCM--they can also set the mileage while doing this.
The other, which I do not recommend, is to have PATS disabled in the tune. The engine will start however odometer will display whatever mileage the donor car had accumulated. Further I had so many problems disabling PATS in the tune, ranging from occasional no-starts to being unable to reverse the change, that I will no longer do it and certainly do not recommend it unless one is feeling lucky that day.
One thing I would do before changing the cluster is to use the HEC self-diagnostic mode (click here
) to observe the engine speed on the odometer display--this will assure that the PCM is sending that data to the cluster. If not the problem lies outside of the cluster.
You can test the tach stepper motor by using the "how to calibrate your gauges" procedure described in this link
If the PCM is sending the data and the stepper motor checks out then the problem is electronic in nature and swapping out the HEC circuit board may be the only fix...
- 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq