Speedo

They suffer from instrument cluster faults , that might be your problem . Could check the various fuses that may be related to instrument cluster

Ford Ranger (2006) – fuse box diagram
Year of production: 2006

Fuse box in passenger compartment
Ford Ranger - fuse box - instrument panel
Ford Ranger – fuse box – instrument panel
Fuse/CB Ampere rating [A] Description
1 5 Instrument panel dimmer switch
2 10 Trailer tow park lamps
3 10 Right low beam headlamp
4 10 Left low beam headlamp
5 30 Windshield wipers/washer
6 10 Radio (RUN/ACCY)
7 5 Headlamp illumination indicator
8 10 Restraints Control Module (RCM), PADI (Passenger Air bag Deactivation Indicator)
9 5 Cluster air bag indicator
10 10 Cluster (RUN/START), 4×4 module (RUN/START)
11 10 Smart Junction Box (SJB) (Logic power)
12 15 Center console subwoofer amplifier
13 15 Horn, Interior lamps
14 15 High beam headlamp, High beam indicator (cluster)
15 — One-touch down relay
16 30 cartridge fuse Power windows
17 15 Turn signals/Hazards
18 — Not used
19 20 Center High-Mounted Stop Lamp (CHMSL)/Stop lamps
20 10 Anti-lock Brake System (ABS) module, Brake-shift interlock, Speed control module, Back-up lamps, Overdrive cancel switch, Electronic flasher (turn/hazard)
21 5 Starter relay coil
22 5 Radio (START), 4×4 Neutral sense (manual only)
23 30 Headlamps (low and high beam)
24 20 Radio battery feed (B+)
25 — Accessory relay
26 2 Brake pressure switch
27 10 Climate control blower relay/blend doors, 4×4 module
28 15 4×4 module battery feed (B+)
29 20 Cigar lighter or power point, Diagnostic connector (OBD II)
30 5 Power mirrors
31 20 Front park lamps, Rear park lamps, License plate lamps, Dimmer switch, Trailer tow park lamps
32 5 Brake switch (logic)
33 5 Instrument cluster battery feed (B+)
34 20 Power point
35 15 Power locks
Power distribution box
The power distribution box is located in the engine compartment near the battery.

2.3L engine (if equipped)
ford-ranger-fuse-box-power-distribution-23-2005
Ford Ranger – fuse box – power distribution (2.3L engine)
Fuse/Relay location Ampere rating [A] Description
1 50** Interior fuse panel (SJB)
2 — Not Used
3 40** Interior fuse panel (SJB)
4 — Not Used
5 50** Interior fuse panel (SJB)
6 — Not Used
7 40* Starter solenoid
8 — Not Used
9 40 Ignition switch
10 — Not Used
11 30A** Powertrain Control Module (PCM), Engine sensors
12 — Not Used
13 30** Blower motor (climate control)
14 — Not Used
15 — Not Used
16 — Not Used
17 40** ABS (motor)
18 — Not Used
19 20** Engine fan
20 — Not Used
21 10* PCM keep alive power
22 — Not Used
23 20* Fuel Pump
24 — Not Used
25 10* A/C Clutch Solenoid
26 — Not Used
27 — Not Used
28 Not Used
29 — Not Used
30 — Not Used
31 — Not Used
32 — Not Used
33 30* Anti-lock Brake System (ABS) (solenoids)
34 — Not Used
35 — Not Used
36 — Not Used
37 — Not Used
38 7,5* Trailer tow (right turn)
39 — Not Used
40 — Not Used
41 15* Heated Exhaust Gas Oxygen (HEGO) sensors, EVAP canister vent valve, Exhaust Gas Recirculation (EGR) stepper motor, Transmission
42 7,5* Trailer tow (left turn)
43 — Not Used
44 — Not Used
45A — Wiper HI/LO relay
45B — Wiper Park/Run relay
46A — Fuel pump relay
46B — Washer pump relay
47 — Engine fan relay
48 — Starter relay
49 — Not Used
50 — Not Used
51 — Not Used
52 — Not Used
53 — Not Used
54 — PCM Relay
55 — Blower relay
56A — A/C clutch solenoid relay
56B — Not used
* Mini Fuses ** Maxi Fuses