I have a 2005 90 HP Johnson 2 stroke and the tach won’t work. It is the system check tach and when I turn the key to acc it performs the system check and sounds the alarm briefly. When I crank the engine the needle jumps up to 4-5k and then goes back to zero and stays there. I have cleaned the contacts on the tach and checked the voltage between the purple and black wires and it read 12-13 V both with the engine on and with the engine off/key turned to acc. I also checked the voltage between the black and grey (signal) wires and it also read 12-13 V with the engine on and also with the engine off/key turned to acc. This is what is weird to me, I read that if the system is working correctly I should see something in the neighborhood of 5.5 V between the black and grey wires with the engine on and 0 V with the engine off.
I know that the voltage rectifier/regulator is a common culprit but if it were the problem the battery would not charge with the engine on, and my battery does charge with the engine on.
I know this is a common issue but all the trouble shooting steps I have read about and performed landed me here.
THE RECTIFIER CAN CHARGE THE BATTERY AND STILL NOT GIVE THE PROPER SIGNAL TO THE GREY WIRE
YOU CAN NOT USE A VOLT METER ON THE GREY WIRE TO DETERMINE IF ITS GETTING THE PROPER SIGNAL
IT IS A PULSE SIGNAL AND A VOLT METER CANT READ THE SIGNAL
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Cannot give the proper signal to the grey wire meaning the rectifier is malfunctioning? I have read that a bad rectifier can cause a fire which I am obviously concerned about. What can I use to measure the pulses? I am thinking someone has tried to maybe bypass the oem plug on the harness and has somehow jumped the purple (power) lead to the grey (signal) lead. I won’t be able to climb back under it until later this week but am trying to get my ducks in a row so I’m not wasting my time once I do.
I DONT KNOW WHAT TO USE TO MEASURE THAT SIGNAL
WE HAVE A GOOD TACH AS A TEST DEVICE
AS FOR JUMPING WIRES, I HAVE NO IDEA HOW TO HELP YOU BECAUSE I DONT KNOW WHAT YOU HAVE
YES THE REGULATOR CAN CHARGE THE BATTERY BUT HAVE SOMETHING WRONG INSIDE THAT DOESNT SUPPLY A PROPER TACH SIGNAL
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When the rectifier went bad on my 1995 88spl (same as yours except I have no voltage regulator), the aluminum body of the rectifier literally melted. Tach got flaky for a few trips and then quit working completely. When I popped the cowling to take look, the rectifier was obviously toasted. They should get warm to the touch when working correctly. But, when they start getting hot they can get ‘take the skin off when you touch them’ hot. If there are other wires or plastic clips or stuff touching it when it starts getting that hot, it would melt straight through any insulation.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
Thanks guys. It’s on a 2006 Key west 176 cc.
I would take it to someone who knows what they are doing like Chris at Charleston Marine.
People will forget what you said…
People will forget what you did…
But people will never forget how you made them feel.
Capt. Justin
I live in Mobile now so that isn’t practical and besides I’m not going to pay somebody to troubleshoot a tach issue.
Just occurred to me that since you have a regulator, your rectifier/regulator unit will be a lot different from that which is on an 88spl (just a rectifier). The heat problem may not be a ‘severe’ on yours as on an spl motor. Either way, be careful. When those diodes in the rectifier go bad, the thing turns into a direct current heating element.
17’ Henry O Hornet w/ Johnson 88 spl
26’ Palmer Scott project hull
14’ Bentz-Craft w/ Yamaha 25
Thanks for the help everyone. I got it figured out-the guy before me was pretty much clueless when it came to wiring and had messed a few things up.