One of the many things that irk me about motor cars are speedo's that are incorrect. My work VVT Toyota Hiace came out of the factory with a speedo that reads 10km/h faster than it should at 100km/h. Even thought the factory did this probably to stop people from getting speeding tickets, the fact that it's incorrect really annoys me. Change the size of the tyres on your car, and the speedo will be out also. By how much depends on how much bigger or smaller than the original tyres the new tyres are. So when I bought my 2003 Jimny with 215/75R15's I knew the speedo was going to be out. Sure I could fix it by marking the display or using gps, but I'd rather have the needle pointing to the correct speed displayed on the speedo.
Whilst in Jaycar the other day buying something for work, I was browsing through the kits section and found a kit # KC5435: KIT - SPEEDO CORRECTOR MK2. It was about $54 so I bought it. A little box to fit the pc board into when finished cost another few dollars. Building the kit was a piece of piss. All you have to have is a basic understanding of electronic components, and an ability to solder.
The finished board looks like this.
Once built, you need to remove your instrument cluster. Remove the 2 screws that holds the plastic shroud in place and gently prise the shroud off with a screwdriver, taking care not to break any of the platic clips that hold it in place. Once the shroud is out of the way, the instrument cluster comes out easily by unscrewing the four screws that hold it in place at all 4 corners of the cluster.
Once you pull the instrument cluster forward, you will find two (or 3 if your car is an automatic) plugs on the back of the cluster. Gently remove all the plugs and move the instrument cluster out of the way.
The plug closest to the passenger side of the car has a yellow wire with a green trace third wire from the end.
This is the vehicle speed sensor wire and needs to be cut to wire the speedo corrector in. On the circuit board the wire 12v+ should be wired into an accesory (I wired mine into the fan circuit). Obviously neg gets wired into earth. Speedo output gets wired to the wire that had been cut coming from the plug that plugs into the speedo, and speedo input wire gets wired into the wire that goes back into the main wiring harness. Once you've done all that, set the unit up as per the instructions that come with the kit. They are pretty straightfoward. You'll need a gps unit to check it against, and you'll need to go for a drive down the freeway to set it up correctly. Once it's all set up, fit the board in the plastic box and secure somewhere under the dash. I cable tied mine securely to the steering column.
Go for another drive to retest unit. Once satisfied that it's correct, screw the instrument cluster back in place and refit the plastic surround. Cable tie wiring out of the way, and voila, all done
