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Tachometer Wiring

mill686

mill686

Regular Contributor
I have an older, yet NOS (1975), Mercury tach. I was wondering if I could use it on my 1984 50HP 4 cylinder? The old tach only has two wires coming from it, a black and a brown and simply 2 terminals, one positive and one negative. If I could use it, could someone please tell me what wires to connect? Thanks.

Greg
 
Thanks. But what color wires do they attach to in the control box?

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Yes,you can.If you are saying that there is a brown wire already attached to the tach,hook it to the grey wire in the bundle,and black to black.Tape off the others. The purple is 12v+,usually used for instrument lights. Tan is a temperature sensor.
 
Hooked it up as desribed, but acted wacky with no true reading. I have an installation sheet that mentions something about a "module". I guess I need that for this outboard. Had this attached to my '69 100HP.
 
When you say whacky,did the needle go backwards?If it did,swap the wires around.
I have a 4cyl '69 80HP,Lovely outboard.Your 100HP is an inline six? And your 50 is an inline four? I truly havenaclue if this makes a difference,but I have a genuine '78 Mercury Tachometer,which I hooked up to the beautiful Merc800, no matter what I do,it will not go above 3000RPM's.I finally give in and bought a modern tach,which works perfectly.A merc tech told me that the Mercury tach may be specifically for a 6cyl.
The module mentioned in the destruction's is a requirement for the 50HP "lightening energizer" system. Think that was the 4cyl's from around the late '60's early '70's.But may be worth a try.Can be found on ebay for outlandish money
 
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Swapped the wires around and again had no luck with readings. This is what I have guys along with the wiring diagram. What else might you guys suggest?
 
I found this out while searching for a tach for my motor. Different motors require different tachs, and get their signals from different places, depending on; the type of ignition, the no. of cylinders, and the type of charging system.
Sell that one and get the right one for your motor, or get a universal one if you want to save money.
 
That is identical to mine.The problem is,I believe,that the tach is for either a six cyl or a Mericrusier stern drive.
The signal for the older inlines was taken from the brown post on the switch-box.But can be hooked to the rectifier to either of the yellow stator wires.Check your rectifier and your stator.
 
The black wire,the ground, at the tach is hooked to the + post,yes +. The brown wire,the signal, at the tach is hooked to the - post.
Motor side.The brown wire is hooked to either of the yellow stator wires at the rectifier. In the past it would have been hooked to the brown post on the old switch-box. Sorry for causing confusion.
 
Do a check on the rectifier.Check the stator.Check for a broken wire between the motor and the tach.Did you try wiring direct to the powerhead? Those analogue tachs are usually pretty bullet proof compared to the modern ones.
 
I'm beyond my range of knowledge on these things. I'll have to swing by one of the boat repair joints in my area and see if they can point out exactly where I could hook it up. Thanks for all of your help.
 
Ok See if this helps.!969 Merc800.Shouldn't be too far out.I stuck the white in there as that's where it would connect to the light if it was there
 

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I tell you what, I'll take a shot of my outboard. Maybe you can determine where they go and show me like you did here. Too dark right now, I'll take the pic and post tomorrow.
 
Thanks. Continuity present when both red and black to ground and opposite contacting either post. I guess I need a new rectifier. BTW...here are those pics I was going to send. Could you connect directly to the gray wire coming from the bundle before it contacts the rectifier, or is that why the rectifier is there? Thanks again.

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Let me ask you this...as long as I get continuity on one post, that indicates continuity on that flow chart. Or do I need continuity or a lack there of from both posts??
 
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You need continuity or lack there of on both posts.
:)Confused me first time around and dumped a perfectly good $65 rectifier/regulator:mad:.I buy most of my parts from the 'States,so work in $'s
 
I ask because I have a neighbor with an older Merc. He has replaced all electrical components except that. Just gets a bunch of cranking.
 
Connect to rectifier where grey wire is connected.
The signal for the tach is from the pulses of the stator
No,bad rectifier won't keep it from starting,if it's an older Merc.Your neighbour needs to check spark,compression and fuel.If there's good spark,3/8",good compression,100PSI+. Clean carb(s).This is a rough guess as we have no HP,year,model.
 
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Thanks again.
His is a 150, unsure of the year. I emailed him the info you provided.

Could I do a quick tach check and connect the brown wire directly to a stator wire, or would that mess stuff up?
 
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