Everything in the cluster works apart from the odometer, ive tried resetting the trip computer but no luck any help is much appreciated, is it possible the guy that sold it to me pulled a shifty and wound it back?

Odometer
The IPC contains a season odometer and a trip odometer. Momentarily press the trip/reset switch on the IPC in order to toggle between the season odometer and the trip odometer. Press the trip/reset switch for greater than 2 seconds, while the trip odometer is displayed, in order to reset the trip odometer. The IPC displays the vehicle mileage and trip mileage as determined by the BCM. The BCM calculates the mileage based on the vehicle speed signal circuit from the PCM. The odometer will display 'error' if an internal IPC memory failure is detected or there is a loss of class 2 communication.

IPC - instrument panel cluster.

Replace the instrument panel cluster (IPC). Refer to Instrument Cluster Replacement .

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If the speedometer still works, you'll probably have to replace the cluster. Chances are a gear broke inside the odometer.

Fords in that era are notorious for broken plastic gears in the assembly. If the Speedometer works and the odometer works but the trip odometer does not work, you can still have a broken or stripped plastic gear. They are very small and cost about $25 but they are a pain to replace. You can send your cluster off to have it repaired by a reputable shop. Just Google instrument cluster repair.

This is right from GMC service repair manual
Odometer
The vehicle odometer is calculated and stored electronically in the instrument panel cluster (IPC). The base IPC contains a season odometer and a trip odometer. The uplevel IPC contains a season odometer and two trip odometers. Momentarily press the trip/reset switch on the IPC in order to toggle between the season odometer and the trip odometer. Press the trip/reset switch for greater than 2 seconds, while the trip odometer is displayed, in order to reset the trip odometer.
The IPC calculates the mileage based on the vehicle speed signal circuit from the engine control module (ECM). The odometer will display 'error' if an internal IPC memory failure is detected. The odometer displays either miles or kilometers as requested by the activation of the Personalization button on the steering wheel controls.

this sounds like a bad speedometer cluster, you stated everything else works so i assume the speedometer is working and just the odometer and trip stopped working and so the speedometer will need replacing. good day.

N13's are terrible for this problem, the odometer stops because of a faulty little nylon cog that has to be replaced, the tacho and gauges in n13 dashed die as well but as far as I know that's because of faulty electronics, if it was just the odometer problem you couldv'e bought the cog off ebay (and with a little mechanical knowledge) you could've taken the dash apart and re installed it yourself but because the other electronics are dying I advise you take it to a dash repairer or you can try getting out a soldeing iron and try to replace all the faulty connections yourself.

you have a bad speed sensor

Since everything else is still working, your odometer just crapped out. This is very common on the Vics/ Marquis that utilize the mechanical style odometer. I've had two of them (1989 and 1991 Grand Marquis) where the odometer failed. You will need to remove the odometer from the instrument cluster and either replace it with a new unit (good luck with that) or send it out to be repaired. There's a guy that does this specific type of repair, search the Internets and you'll find him.

Side note: Since it was only the main and not trip odometer that failed on my two Panthers, I learned my lesson the second time around and just kept track of my mileage using my trip odometer and a pen and paper in the glove box. A lot easier than tearing the dash apart at the time. If it happened now on my current car ('94 Vic LX), I would fix it. It's not a really hard repair if you know what you're doing or can find someone who does to give you a hand.

Section 13-01: Instrument Cluster—Conventional 1995 Thunderbird, Cougar Workshop Manual REMOVAL AND INSTALLATION Instrument Cluster Removal and Installation

1. Disconnect battery ground cable (14301) .

1. Remove screws holding instrument panel reinforcement (017A28) .

1. Remove screws holding instrument panel lower shield (045G02) .

1. Remove fasteners holding steering wheel column as outlined in Section 11-04 . Gently lower steering column.

1. Remove fasteners holding the instrument panel finish panel (044D70) and gently pry off.
   
   
   
   

1. Remove four instrument cluster retaining screws. (Do not remove screws from the instrument cluster main lens (10887) and instrument cluster mask (10890) ).

1. Slide the instrument cluster (10849) to the right of the instrument panel opening and unhook the instrument panel harness from the back of the instrument cluster .

1. Remove the instrument cluster from the instrument panel (04320) .

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Speedometer/Odometer Federal law requires that the odometer in any replacement speedometer (17255) must register the same mileage as that registered in the removed speedometer . Since the speedometer mileage cannot be reset on this unit, affix odometer sticker to driver's door pillar and record original vehicle mileage. Removal

1. Disconnect battery ground cable (14301) .

1. Remove the instrument cluster (10849) as outlined.

1. Remove seven screws retaining the instrument cluster mask (10890) and instrument cluster main lens (10887) .

1. Remove speedometer assembly.

Installation

1. Position the speedometer assembly to the instrument cluster back plate (10848) and install.

1. Position the instrument cluster mask and instrument cluster main lens to the instrument cluster back plate and install the seven retaining screws.

1. Install the instrument cluster as outlined.

1. Connect battery ground cable and check the operation of the speedometer .

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