Bike is a 2007 track bike, been stripped down recently and putting things back together and notice I now have no MPH reading on my dash, just sits at 0 when running in gear. Everything else seems to be working fine (revs etc..) I checked the basics..fuses, connectors and all looks ok. Consulted my Haynes manual and proceeded to check the speed sensor mounted on the engine underneath the fuel tank. Tapped the pink (signal) wire from the sensor and reads a constant ~5V. Rotating the rear wheel I was expecting it to fluctuate from 0-5v but nothing. Am I right in thinking the speed sensor is faulty? sensor pic for ref;
Not necessarily. I would have thought that the signal is a pulse. Check the resistance of the green wire to earth is low so you know the negative side is ok and measure the voltage on the black wire (brown/white on the loom side) with the bike running, should be +12v so you know the sensor has a working supply. The only other thing to check is the resistance of the pink wire through to the dash connector to confirm continuity. It's the same colour at both ends, but runs through another connector somewhere in the nose fairing.
So further testing proved I had no 12v+ going to the sensor but there was power going to the other plugs running from the same line and fuse so deduced it must be a break in line somewhere. After ALOT of tracing and testing I found a section of wire I had cut out the tail section, after stripping back the tape shows the 12v+ bridged across 3 wires. Turns out this feeds the speed sensor + rear light + number plate light.. Who'd of thought! twisted the ends together and boom, we have power and MPH. Took a photo of the offending connection found in the tail section for reference;
Good find. The alternative would have been to run a new 12v feed to the sensor, but at least you managed to find the original supply wire and fix it. Well done.
