Logo
FULL SITE MENU

Tachometer Wiring

bill_w

bill_w

Advanced Contributor
Is there any way to check the wiring for a tach, to see if its defective, or to test the tach itself? The one on my 83 115hp Johnson moves a bit when the key is turned on, but that's it. There are 4 wires going to it, blue, purple, grey, and black. I assume this was installed along with the rest of the gauges in 85, the year of the boat (all OMC gauges). The tach is set for 4 pulses/rev.
thanks, BIll
 
No, I haven't. It was set on 4 when I pulled it out. If I remember right, there are settings for 2, 3, 4,and 6. I figured the pulse setting match the no. of cylinders. I'm pretty sure the blue and black wires are power and ground for the backlight, and the grey and purple are signal wires for the tach.
 
Like I said I know little other than what I have read on outboard forums,If I remember correctly the tach setting should match the poles on the alternator?? or the stator I dont recall, and from what I have read they were closer to 6-8 poles,I dont think it will hurt the tach to try the 6 pole setting if there is a 8 I'd even try that.Or just google it see what comes up
 
Last edited:
The wiring is as follows:
Purple = B+ (positive)
Black = ground
Grey = pulse signal from rectifier/regulator
Blue = instrument light (positive) from nav light switch.
Testing:
Test that engine charges properly, min 13,5V at about 2500 rpm
If OK, use s separate signal wire from terminal strip on engine (yellow/grey) to rev counter -Grey.
Set pulses at 6 on rev counter. Use a small screw driver and 'wiggle' the setting screw a bit to be sure you have contact inside, might just be corrosion if not working.
 
Thanks Haff..I'll try that tomorrow or Sat, and let you know what happened. It just might be corrosion, the boat sat for a couple of years before I got it.
 
One of the MOST common tach errors on a V-4 is the rectifier. They actually go bad 3 to 4 times faster then any other electrical part. You need to see if the battery is charging as stated above....... do a search for rectifier testing and there are simple multimeter tests. I Just replaced mine and I have a friend that had the same exact problem in the same week. The part is fairly cheap and available here on marineengine.com
 
OK, did some testing on the weekend. First of all, its NOT charging. Second, third, etc, etc, to about 10th, its a wiring nightmare. The original powerhead was swapped out for a newer one, and the engine wiring has been changed, swapped, spliced, to the point where I don't know whats going where. I've posted pics under "198?? 115 Johnson". I hope its as simple as a rectifier, but I somehow think I've got a real can of worms. Anyways, lets carry this onto the other post.
thanks,
Bill
 
Back
Top