speedo Not working

[hondaguy]

My '03 mercury speedo is not working and tacho is surging or constantly changing revs as well. Boat has sat for about 4 months. Thinking it is an earth or corrosion problem somewhere. I did replace the steering cable about a year ago and may have disturbed something in the wiring loom then. Question is how does the speedo senor work on a mercury? Is it electrical on the motor or is a water pressure on the front of the leg? Have no idea of where to start apart from looking for loose or corroded wires.

[Noelm]

most speedos are driven by a hose and pressure, unless you have a "paddle wheel" type that comes with GPS units, if it has been sitting for a while, I would be looking for a Wasp/Spider/Ant nest in the hose end!

[hondaguy]

no paddle wheel that is why I thought it may have been a pressure set up somehow

[blueline]

no paddle wheel that is why I thought it may have been a pressure set up somehowhey mate on the bottom of the leg you will see a hole, there should be a hose at the back of the speedo undo it and give it a blast of air(from an air compresor) should clear any blockage, but in saying this i dont know how the new digitle ones work.

[hondaguy]

This one is a anologue dial type and not digital screen type. Will try the blast of air first up.