Tach gray wire short?

[Dr.Dan]

I have a 1999 90hp v4 60 degree Johnson. A while back the tach stopped working so I replaced it.

Still didn't work.

So I replaced the rectifier/regulator.
Still nothing.
All system check lights come on when I turn the key to on, and the tach needle goes to zero.

I tested the two yellow wires from rectifier and they are putting out about 14.5 to 15v.

Tested gray wire at rectifier and it is about 8 to 9v when it is unplugged from boat harness.

When I test gray wire at tach it is zero volts.

So I tested gray to ground and it has continuity. Plug by plug I disconnected the gray wire and discovered the short to ground lies between the six pin plug at the engine, that includes a gray, tan, black, and other wires, and the 8 pin plug at the tach that also includes a gray, black, purple, and other wires.

The 6 pin plug where it seems to be grounding out at the engine goes to the vro pump and then to the tach, per the wiring diagram. Would it be normal for the gray wire to show ground continuity at the vro? Or is it shorting out to ground? The vro appears to work fine at idle (oil is producing smoke out exhaust) but I have not tried wide open yet.

If the gray is supposed to ground out at the vro, how does any current go down the sender wire to reach the tach if the sender wire is grounding out at the vro?

I can't even find where the gray wire that comes out of the rectifier splits to the six wire connector and to the vro. I assume it splits off after the connector since that is where the ground short appears to be. Does anyone know where I can find where the gray wire splits off to the vro? Or is there a hidden terminal board somewhere?

Any guidance is appreciated!

 

[oldboat1]

should be diagram in your shop manual. Try ebay if you need a manual.

 

[Dr.Dan]

Thanks but I have the diagram. But it does not indicate how or if the gray wire should be grounded. It just shows the tach gray sender wire tied into the gray wire going to the vro. It does not show what kind of connection it is.

 

[Chris1956]

I have a '98 Johnny 60*V6, which is real similar.

The engine has two 6 wire connectors, giving two 6 wire harnesses. At the dashboard these two 6 wire harnesses are interconnected to become an 8 wire System Check Tachometer plug, a 6 wire plug for the ignition key and 3 ring terminals for a standard tachometer.

I would first inspect the wiring harnesses at the engine, where they connect to the boat harness. I found melted wires at that location. Next check is under the dashboard, where I also found melted wires. Make sure the ring terminals are not shorted together as well.

You already found the grey wire is shorted to ground somewhere, and now you need to find the short.

Hopefully you still have the old VR. It may still be good.

 

[Dr.Dan]

Thanks Chris1956!

I did not realize there are also 3 ring terminals for a standard tach under the dash. I have been under there a fair amount and don't recall seeing extra wires hanging down but I also wasn't really looking for a free wire (I was focusing on the 8 pin plug on the tach). If they are just exposed rings then perhaps the loose send /gray wire has been grounded or are touching (as you noted) by accident as all "loose wires" under the dash have been collected together and wire wrapped into a neat bundle. That sounds like a place to start looking.

I did not take off my vro as I was hoping I would find a wire short somewhere and keep the vro in place. Once I check under the dash I will go back and find all wires and connections under the engine -- so far I have only checked the harness from the rectifier/regulatory to that first harness (the six wire harness that only has 5 wires in it, including gray, and it has a plug in one the spots where a wire was meant to be). I have not followed that harness to the vro yet...but it will be next after the dash inspection.

I am heading out of town today so can't check but will do so early next week.

 

[cfauvel]

the grey wire to the VRO is a tach pulse that does NOT drive your tach on the dash.

The tach pulse to the VRO is used internally to count the number of pulses. There is an IC chip that counts the pulses. As the VRO pump works properly it closes off a contact momentarily to reset the pulse count. If the IC chip gets to 8192 pulses without resetting, it sounds the no-oil horn.

There should be ANOTHER grey wire that goes directly to the tach on the dash, via the main wiring harness.

You can unplug the VRO pigtail to eliminate it being the short (I doubt it is)
BUT DO follow the purple wire and grey wire FROM the vro to where they are coming from looking for a short...they should be wires that you can disconnect at a distribution block behind the flywheel to completely eliminate THAT from being the culprit.

 

[Dr.Dan]

Thank you cfauvel.

I did not think that same gray wire from the vro ran the tach, but the wiring diagram does show that the two gray wires (one to vro, one to tach) are connected using a "connector". I was thinking either the vro was grounding it out, or the "connector" was grounding it out, or somewhere along the wire the grounding was occurring.

My challenge so far is that I can't find the "connector" that connects the 3 gray wires (one to rectifier, one to vro, and one to tach) and the diagram shows it as a connector and not as s terminal strip.

I plan to check the underdash wires first, then the vro connections to see it is shorted out, and then (as a very last resort) I can pull the flywheel. Sounds like little fun there!

Thanks for the guidance!

 

[Chris1956]

When I said VR, I meant Voltage Regulator.

 

[Dr.Dan]

When I said VR, I meant Voltage Regulator.

Thanks for that clarification, Crhis1956!

I do still have the old VR and I already put it back in since the old and the new VR gave similar voltage results when tested, and both failed to make the tach work! I will keep the new one until the tach works, though, just in case!

 

[Dr.Dan]

I want to thank everyone for their feedback!

Chris1956 your comment about the wiring harness having not just the pre-wired OMC System Check connector but also free gray, black, and purple wires with ring connectors saved the day.

I had bundled all extra wires together under the dash and the gray wire's ring terminal was grounding out. A bit of tape and the tach works -- finally!

You have no idea how many hours I have tinkered with this thing.

Thanks everyone!

 

[cfauvel]

Thank you cfauvel.

I did not think that same gray wire from the vro ran the tach, but the wiring diagram does show that the two gray wires (one to vro, one to tach) are connected using a "connector". I was thinking either the vro was grounding it out, or the "connector" was grounding it out, or somewhere along the wire the grounding was occurring.

My challenge so far is that I can't find the "connector" that connects the 3 gray wires (one to rectifier, one to vro, and one to tach) and the diagram shows it as a connector and not as s terminal strip.

I plan to check the underdash wires first, then the vro connections to see it is shorted out, and then (as a very last resort) I can pull the flywheel. Sounds like little fun there!

Thanks for the guidance!

My purple and grey wire connecting points (225 hp V6 (1986)) is under a black cover between the two powerpacks....it is a terminal strip with plastic separating the wires ....so all the yellows go together, all the purples go together, all the greys go together there, under their respective screws. If that makes sense....not sure on your engine...but imagine similar.

 

[cfauvel]

I want to thank everyone for their feedback!

Chris1956 your comment about the wiring harness having not just the pre-wired OMC System Check connector but also free gray, black, and purple wires with ring connectors saved the day.

I had bundled all extra wires together under the dash and the gray wire's ring terminal was grounding out. A bit of tape and the tach works -- finally!

You have no idea how many hours I have tinkered with this thing.

Thanks everyone!

Awesome find

 

[Dr.Dan]

My purple and grey wire connecting points (225 hp V6 (1986)) is under a black cover between the two powerpacks....it is a terminal strip with plastic separating the wires ....so all the yellows go together, all the purples go together, all the greys go together there, under their respective screws. If that makes sense....not sure on your engine...but imagine similar.

cfauvel, I see in the wiring diagrams that most of the outboards have terminal strips like your engine has. For whatever reason on my engine (v4 60 degree) they don't show it on the wiring diagrams and instead show a "connector". Go figure!

 

[cfauvel]

cfauvel, I see in the wiring diagrams that most of the outboards have terminal strips like your engine has. For whatever reason on my engine (v4 60 degree) they don't show it on the wiring diagrams and instead show a "connector". Go figure!

Well that IS a bummer...