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Message |
    
noah sohn
Member
Username: jknoah
Post Number: 19
Registered: 01-2009
| | Posted on Friday, July 17, 2009 - 09:51 pm: | 
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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! |
Kirk Bawiec
Member
Username: smplsoft
Post Number: 46
Registered: 06-2009
| | Posted on Saturday, July 18, 2009 - 06:20 am: |
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Look at the back of the Tachometer. There should be a little rotary switch. Set the arrow on the switch to point to (6P). |
noah sohn
Member
Username: jknoah
Post Number: 20
Registered: 01-2009
| | Posted on Saturday, July 18, 2009 - 06:50 pm: |
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No, There isn't any selector switch on back . |
Graham Lamb
Senior Member
Username: galamb
Post Number: 5705
Registered: 05-2007
| | Posted on Saturday, July 18, 2009 - 06:56 pm: |
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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).. |
Noel McBride
Advanced Member
Username: haventaclue
Post Number: 214
Registered: 05-2007
| | Posted on Sunday, July 19, 2009 - 03:56 pm: |
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Noah,is the tach marked as + - & sig? or white and black in bulb,+ & - ? |
noah sohn
Member
Username: jknoah
Post Number: 21
Registered: 01-2009
| | Posted on Monday, July 20, 2009 - 01:33 am: |
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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 . |
Noel McBride
Advanced Member
Username: haventaclue
Post Number: 217
Registered: 05-2007
| | Posted on Monday, July 20, 2009 - 04:43 am: |
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Connect white to white directly not via post,black to pos(+) and brown to s or neg(-). No I'm not of my rocker  ,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. |
noah sohn
Member
Username: jknoah
Post Number: 22
Registered: 01-2009
| | Posted on Tuesday, July 21, 2009 - 07:08 pm: |
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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 .    |
Noel McBride
Advanced Member
Username: haventaclue
Post Number: 220
Registered: 05-2007
| | Posted on Tuesday, July 21, 2009 - 07:54 pm: |
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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. |
noah sohn
Member
Username: jknoah
Post Number: 23
Registered: 01-2009
| | Posted on Wednesday, July 22, 2009 - 07:27 pm: |
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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 McBride
Advanced Member
Username: haventaclue
Post Number: 223
Registered: 05-2007
| | Posted on Wednesday, July 22, 2009 - 07:46 pm: |
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You can also test the tach harness plug the same way,put three jumpers in to the plug,verify the white and the ground,if you get no power or sig then the problem is somewhere between there and the motor. http://www.maxrules.com/oldmercs/Wiring/1966ona/30.gif .Here's a diagram of the wireing |
noah sohn
Member
Username: jknoah
Post Number: 24
Registered: 01-2009
| | Posted on Friday, July 24, 2009 - 09:12 pm: |
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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? |
noah sohn
Member
Username: jknoah
Post Number: 25
Registered: 01-2009
| | Posted on Saturday, July 25, 2009 - 12:34 am: |
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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?   |
Noel McBride
Advanced Member
Username: haventaclue
Post Number: 226
Registered: 05-2007
| | Posted on Thursday, July 30, 2009 - 06:11 pm: |
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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. |
Noel McBride
Advanced Member
Username: haventaclue
Post Number: 228
Registered: 05-2007
| | Posted on Saturday, August 01, 2009 - 09:58 am: |
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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 |
noah sohn
Member
Username: jknoah
Post Number: 26
Registered: 01-2009
| | Posted on Sunday, August 02, 2009 - 08:39 pm: |
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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. |
Noel McBride
Advanced Member
Username: haventaclue
Post Number: 234
Registered: 05-2007
| | Posted on Monday, August 03, 2009 - 08:43 am: |
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I hope it works for you,don't forget to let's know  |
