Boating How-To’s - tech pags now what?

I just got an 85 18' SunRunner with a 140HP Merc I/O and the tech pegs (max's out/reads as high as it can) as soon as you turn on the ignition (don't even have to start the motor).

I played with it some and its connections...

The tech will do 1 of 3 things...none of them are the correct function...read nothing, peg, or read a steady aprox 4000 RPM regardless of engine speed.

Seemingly connected correctly (as the boat came when I picked it up)....Grey goes to the signal terminal, Black to the Neg. and Purple to the +. This is when it will peg. If I just switch the + & - it will peg. If I swap the + or the - for a confirmed + or - (assuming a bad ground or such), I get the same thing...no change....just pegs.

If I swap the Neg. and the signal wire, it reads zero when turned on and when I start the engine, it reads about 4000 rpm even if I rev the engine.

If I swap the + and the signal wire I get zero reading at all.

What should I be doing from here? New tech or fix wiring issue?

I am fairly mechanically inclined, although I am new to this boat and it's wiring is a bit more complex that what I have previously done some work on (my father-in-law's boat, a 19' w/ 60HP Johnson O/B)...

Please advise...

THANK YOU!!!

Sounds like you have a bad tach ; you have it wired correctly and there isn't any calibration you can really do to it. As far as wiring goes, the wiring is roughly the same as the other boat you spoke about, as far as standard colors, etc. You could try swapping the tach with another but you wouldn't be able to use one from an outboard because most of those are made for Outboards only, and are set based on the pulse number that works with specific brands, etc.

Okay...so it appears that the tach is bad...suggestions on where to find a cheap good tach...I'm guessing a mail-order would be a little slower but cheaper ay?

Okay...so it appears that the tach is bad...suggestions on where to find a cheap good tach...I'm guessing a mail-order would be a little slower but cheaper ay?

It all depends on how fast you want it and what tach will look close to the other guages you have; you can probably pick up one at a local dealer for close to what you pay for the tach and shipping,etc, and even if its $10-15 more, you will have it then and not have to wait. Sometimes you can order a tach that looks the same as what you have by searching online easier, but it all depends on what you need or want. Im fortunate that I can get parts at dealer cost, because my family owns a dealership, but I can still find deals online that are cheaper than they can purchase it for. Overtons has free shipping always and good prices,so its a good option if you can get one from them, especially with the free shipping. Good luck, if you lived closer I would give you one of the 6 that I have in my toolbox.