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Tacho meter connection

jknoah

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"Hello, mr Lamb or someone who

"Hello, mr Lamb or someone who can help me.I got another issue to solve.I 'm going to connect a tacho meter to my old mercury 80HP motor, serial# 5006372(78').I purchased a matching old merc tacho meter with 3-plong connector from Ebay.When I got the tacho meter,its needle stayed at about 1500 R.P.M then I hooked it up to the control box and turn on the key(not start, run position) The needle moves up at 4500 R.P.M and then I start and run the motor ,the needle stuck all the way maximum high. What is the problem? The voltmeter reads about 12V with engine off and goes up 14V with engine running so I think rectifier is working fine.The 3 wires from 3-plong connector connected like this. The Black goes to negative post & meter housing,the white goes to light bulb post(+) and the brown goes to signal post . please help!"
 
Look at the back of the Tachom

Look at the back of the Tachometer. There should be a little rotary switch. Set the arrow on the switch to point to (6P).
 
Sounds like you bought a bad t

Sounds like you bought a bad tach. It should go to zero once power is applied and the motor is not running (the needle can sit anywhere without power)..
 
"I remember it marked as 1st

"I remember it marked as 1st post has no marking(supposed to connect light bulb holder only,white wire) , 2nd post has NEG-ative & 3rd post has S but not sure. I 'll check it tomorrow and let you know ."
 
"Connect white to white direc

"Connect white to white directly not via post,black to pos(+) and brown to s or neg(-). No I'm not of my rocker
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,some might differ, I have a beautiful 1969 merc800 and I bought an old style tach to go with it and that's what the instructions stated,but then I had the white and black in the bulb and only the pos(+) and neg(-) posts. The fact that the needle goes to the limit when switched on indicates wired back to front.
I'm working on the assumption that the tach is an annalogue so there are no circuit to blow."
 
"sorry, I'm late Noel. I s

"sorry, I'm late Noel. I show you the pictures. the tachometer and cable connector has come like this.The seller said this is a working part. I confused the posts and connections.As you see the pictures, There are only two posts. the left top is positive which is connected and jumped to the meter body with black wire and the right top is negative which is connected with brown wire and the center white wire is lamp holder.I hooked it up and turn on and run the engine but the needle didn't move it .
289242.jpg
tacho meter pic"">
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thcho2"">
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tacho3
 
"Noah that is wired ok,I'm

"Noah that is wired ok,I'm afraid you are going to go back to the control box and test your connections there.First you might want to test the tach by wiring jumpers directly from your motor,white from the white terminal on your switch box to lamp,brown from brown terminal on switch box to neg(-) or hook brown to one of the yellow wires on your rectifier,on newer motors than mine the tach is hooked to the rectifier,and any ground to the pos(+). This will tell you if the tach is working before you start to dismantle control box. This tach is identical to mine,except I have a black wire exiting from the lamp holder alongside the white."
 
You think there may be a wirin

You think there may be a wiring problem between the motor and the control box.OK I'll connect the tacho directly to the motor as you say then test it again tomorrow.
 
"Noel, still it doesn't wo

"Noel, still it doesn't work. I followed up what you said. I checked wiring between the motor(switch box,rectifier) and control box and no problem found.When I turn the key on , the white(+) and black(-) has power and the brown is connected rectifier.This time ,The tacho needle is going down to 0 RPM when the key turns on so it seems like works but the needle just keep sitting and vibrating there while the motor runs and doesn't response the motor speed. Is The problem by a faulty tacho? or any other thing?"
 
"From EBay I found a similar t

"From EBay I found a similar tach meter but this one has a tacho module(see pic).Because lack of this ,My tacho does not work?
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tacho module"">
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tacho module2
 
"Hi noah, sorry I didn't g

"Hi noah, sorry I didn't get back sooner,lines down,no phone ,no internet since last Saturday afternoon. I had forgotten about the module ,but I was told when I was installing mine that the module was used on older motors and I didn't require it as my beautiful merc800 is 1969,I didn't need it. However,I could never get my tach to reach the rec.rpms. So I probably would have needed the module but was unable to find one.
If it's not too late I,and this is my personal opinion,would bid/buy,and if it didn't work,well and good,put it back on ebay,and if it worked so much the better.
If you missed it you could try a merc dealer for the module only and give it a go_Oh the tach I have, now sits unused in the garage and the date on it is 1978."
 
"I was reading other posts on

"I was reading other posts on the forum,could your rectifier be done,you could also try hooking the brown tach wire to the brown post on the switch box.This is where this tach was originally designed to work from.But should work equally well from the rectifier"
 
"I purchased a tach module fro

"I purchased a tach module from EBAY. It's a NOS and cheap, paid $20 for it. The seller said before 86' all Merc 4-cylinder motors(thunderbolt ,lighting energizer) require this module for a tacho meter .Now I'm waiting it delivered ,I hope it make the tach works this time. I'll tell you how it works or not."
 
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