Nissan NS70A Tach problems

[wolfe1978nm]

Recently got a NS70A and have it running like a top after a lot of cleaning and tuning/tightening.

However the previous owner pulled all of the electrical and gauges and put in a new simple electrical switch into the boat. They have it wired so there is a "master" switch that controls all power to the boat, including the key. This has been running fine until we put gauges in the boat.

Trim and fuel are fine, work great.

Tach is not working. We have a grey lead off the engine with a pulse (It was still under the dash from the original wiring), but for some reason that pulse only appears when the master power switch is OFF, then we get a tach reading. When the master is ON the tach will go from dead to a zero resting position but will not show a reading.

So master power OFF, tach rests on the peg then shows proper RPM when the engine is started. Master power ON it jumps up to zero and sits there and will not show RPM. 12v and ground coming off the same connections as everything else is run on.

Not a bad tach, although it is a generic older tach (three leads). Tested with a multimeter with RPM setting and it agrees... when the master power is on there is NO PULSE coming in on the grey lead, when master OFF there is a pulse.

Also, if the tach is connected to 12v/ground then there is a light whistle coming from the control box... disconnect the tach from power and it goes away. The whistle stays on all the time even when the engine is running if the master power is on and the tach has power. (It isn't the heat sensor, we verified that, it is a different and much louder beeper).

So there is something I am missing about how this tach needs to be wired. Does it require a specific ground directly off the engine? Anything else that I may be missing before I pull all the wiring and recheck it all?

 

[pvanv]

Re: Nissan NS70A Tach problems

Trace the wiring back from the meter to the motor. Sounds like a missing ground or mis-wired power somewhere. A full diagram is available at http://www.nissanmarine.com/tech_talk/pdf_files/Nis50C-60A-70A.pdf

 

[wolfe1978nm]

Re: Nissan NS70A Tach problems

Trace the wiring back from the meter to the motor. Sounds like a missing ground or mis-wired power somewhere. A full diagram is available at http://www.nissanmarine.com/tech_talk/pdf_files/Nis50C-60A-70A.pdf

Well as luck would have it we ran across a complete M70A with controls, minus the foot. Picked it up cheap.

So at this point I think we are going to try and replace the control box with the new one. New controls look great and the old ones are badly wired and the choke has been rigged with a replacement toggle.

However, looking at the wiring it seems really odd. Pigtails coming from the control box we have red/black/white/green. The wiring shows it uses white/black and then looks like blue connects to the terminal... so I'm lost as to why the manual would have different colors than either a NS70A or a M70A.

I'll check back in when we have the new controls in with the new wiring harness to see if that improves things.

 

[pvanv]

Re: Nissan NS70A Tach problems

Check you diagrams again.

 

[wolfe1978nm]

Re: Nissan NS70A Tach problems

Should have mentioned we don't have a Nissan/Tohatsu tach, think the ones we have are both OMC.

Will that tach work on a NS70A?

The reason I'm back to asking about it is because we completely gutted all the wiring and put in the new controls today. This was from a Tohatsu M70A. Everything went in fine and using the white/black the tach does work but it also requires 12v on another lead.

The problem is there is an alarm when the motor is put in gear, but not in neutral. Checking the wiring it all comes down to the neutral switch. It is like the control box is in alarm to let you know it is in gear when the motor is off, but it stays that way when the motor is running to... alarm in forward/reverse but not in neutral, running or not.

So is there something in a Nissan tach that tells the switch to disable the alarm when the motor is running? Nothing else makes sense.

And it isn't related to the overheat sensor, it is not even connected as the new controls don't have lead for it (unless the green pigtail from the controls is used for that, wiring diagram shows it not even used).

Oh and the alarm is sounding regardless if all the accessories/gauges are hooked up or if they are all disconnected.

 

[wolfe1978nm]

Re: Nissan NS70A Tach problems

Seem to have solved my own problem. Just going to post results in case anyone else runs into this issue.

Apparently not all NS70A / M70A are wired the same way, even with the wiring harness working perfectly on almost everything.

The alarm wiring coming out of the control box is meant to use the yellow leads all the way back to the overheat sensor. However on my NS70A the yellow lead in the harness leads back to the magneto and was supposed to be the tach connection.

So now the single lead has to be run from the overheat sensor to the yellow lead coming off the buzzer inside the control box, and the existing yellow/yellow connection inside the box disconnected.

That essentially solves the issue of updating from the old chrome style of control box to the later plastic style that is more in line with current controls (push-key choke and such). All the other connections should work fine, the only other adjustment is removing the 2-lead trim wires the run outside the harness on the older controls and hooking them into the leads that run inside the new harness and split off at the plug.