​1989 Johnson 70 Warning Horn Seems Faulty - Do I need it under my Circumstances?

[sumocomputers]

​1989 Johnson 70 Warning Horn Seems Faulty - Do I need it under my Circumstances?

I have a 1989 Johnson 70, which fails any warning horn tests of grounding the 3 tan wires with ignition on (VRO, oil tank, engine temp sensor tan wires). This leads me to believe the buzzer itself is faulty.

I understand that the warning horn alerts for low oil, no oil, and engine over-temp. The buzzers are not cheap at $65-85 for such a little thing, and the control box looks a little scary to open up.

Also, it seems the S.L.O.W system would slow the RPMs if it gets above 203F (assuming the S.L.O.W system is working!).

Since I am very likely going to disable the VRO2 system in the next few days, and I have just installed a new Sierra Temp gauge and sending unit, how important is to test and likely replace the warning buzzer?

And if you recommend I should get in there to test the buzzer, could I just apply 12V directly and verify it that way? The official service manual doesn't really address accessing or testing the buzzer, so just trying to get some direction on the best way to go.

Thanks,

Chris

 

[Bosunsmate]

Well since you a premixing you can cross out the vro issue.
With the sending unit thats good to have but it wont alert you like a horn does. I recently ripped mine out as i thought id put it on my tractor as i just dont look at it on the boat.
Id rip into that control, it isnt too hard to put back together. Check that the control box still has a good ground connection too

 

[Bosunsmate]

Thats checking that the ground wire to the control box is ok. ie check the control box has continuity with the neg battery terminal

 

[emdsapmgr]

The only way I'd run that engine without an overheat horn is if you installed a temp gauge on the dash and a dedicated sender on the head. That would cost about what a new horn would.

 

[sumocomputers]

I will see if I can check a good ground at the control box. Do I need to open it up for that, or can I do it from the outside?

And I do have a new dedicated Sierra temp gauge with sender on the block, and I do keep a very close eye on it.

 

[Bosunsmate]

I will see if I can check a good ground at the control box. Do I need to open it up for that, or can I do it from the outside?

And I do have a new dedicated Sierra temp gauge with sender on the block, and I do keep a very close eye on it.

Yes the whole metal outside of the box should be neg/ground

 

[Fed]

The horn doesn't need the box ground to work but it does need the purple wire to be hot when the key is in the ON position.
Could have a key switch problem.
Gauges are great but looking away for a minute could end in tears.

 

[gm280]

Before going to too much effort. Try verifying the actual horn buzzer or whatever you call it first. It is either going to take a ground to make it work, or a positive voltage. Find out which it needs and force it to sound. If it does work, then go after the other possibilities. You could be fighting a bad horn and everything else is okay. But you need to prove that first...

 

[Fed]

It needs a +positive on the purple wire and a -negative on the tan wire for a continuous beeeeeeeeeeep.
All other beep beep beep signals are created at the vro pump & oil bottle switch... I think.

 

[Bosunsmate]

It needs a +positive on the purple wire and a -negative on the tan wire for a continuous beeeeeeeeeeep.
All other beep beep beep signals are created at the vro pump & oil bottle switch... I think.

Ive got a 1982 that has a beeeeeeeeeep when the tan wire is grounded for an overheat situation.
It also does a little beep when i turn the ignition on to tell me its working. For that to work it must have a neutral/ground circuit which isnt from the tan wire.
I dont have a VRO so something else is going on to create that neg/ground...
I suppose it might have a capacitor that somehow limits current flow at start up and another circuit which has a break which is open to ground and complete when the tan wire grounds.... i guess?

 

[sumocomputers]

Hey guys, appreciate all the suggestions. I think I do want to verify that the buzzer itself is working. Anyone had experience opening up an OMC control box? The service manual makes it look kinda scary, I just don't want to screw up any of the throttle controls, etc.

 

[Bosunsmate]

Those service manuals always do quite well at making something relatively easy seem like its NASA spec.
Take a photo of it if you want and post it here, im sure heaps of people will have delved into the same one before.
They arent difficult, just a bit fidley and just make sure you dont drop any parts under the floorboards

 

[Bosunsmate]

Ive looked up the diagram for your control box, if its the same one that came with the motor then its a general standard one,
First time you open them up and try and put them back together they are a bit tricky as you need to get the throttle control and fast idle thing to slot into the right place but it shouldnt take more than a minute or two to get that right. After doing it once the second time is too easy.
I lay mine on its side when undoing it that way when you lift it apart you can see where things have being.

The horn is easy to access on the top rear

 

[Fed]

I haven't pulled mine apart so I can't help you there but I can tell you the purple wire also goes to the 3 pin socket so you could test there. Do you have gauges and do they work because that is the power supply for them.

Interesting Bosun, my controller doesn't beep as a self test but I have no idea what year model it is.
Thinking maybe it's old and the self test is a newer improvement or maybe mine is faulty.

 

[sumocomputers]

OK fellas, I am going to give it a go. And I think I will try to lay it on the side so I don't lose any parts, great tip.

From what I read, mine should have the momentary beep when key is first turned on, and it isn't, nor are any of the 3 sensors.

As for what triggers the alarm, I think 12V is always present (with key on) at the purple buzzer wire, and if any of the 3 sensors trigger, they essentially short the tan wire at the buzzer to ground, and result in a solid beep, intermittent beep, etc. depending on the sensor behavior.

And Fed, I do have a Tach that is wired to the 3 pin and it works (after you thump it), and I just looked at the wiring diagram and I see what you mean. I believe that I will still need to open it up and apply power directly to the buzzer to verify that the buzzer is good or bad. I fear it is bad, and they are $65+. I am thinking if it is bad, I may see if I can find a cheaper external buzzer and just ghetto-rig it with a pigtail for under $10.

I'll report back.

 

[64osby]

Maybe a big bright red light mounted right in the middle of the dash.

 

[Bosunsmate]

Interesting Bosun, my controller doesn't beep as a self test but I have no idea what year model it is.
Thinking maybe it's old and the self test is a newer improvement or maybe mine is faulty.

Sounds like its pre 1982 at least. I think mine has three wires so his probably will too.
The self test is great. My only concern after hearing that beep before start up is knowing whether the actual sensor/sender is working, they are quite pricey so its not part of even my long term maintenance. I suppose i could heat the area up with a torch but im probably bound to ruin it while testing it, seems the same problem as they have with quantum mechanics!

 

[Bosunsmate]

Fed I am quite sure yours is the two wire older model with the tan wire providing any ground and thus completing the circuit, and also therefore not having the self test

 

[sumocomputers]

No Title

So I dug in today and took apart the control box to see if I could verify the buzzer was bad. Short story, it certainly appears to be.

First thing I noticed is the buzzer has 3 wires: Black to ground, Purple (seems like 12V+ since it also goes to the accessory/tach wire), and Tan, which I assume ultimately go to all the sensor feeds. Couldn't recognize the wiring diagram for the buzzer in the service manual, so just had to fly blind.

Next I just did some voltage checks for the following:

KEY ON ALL SENSORS HOOKED UP
Purple & Tan = 3V
Purple & Black = 12V
Tan & Black = 9V

KEY ON ENGINE TEMP SENSOR GROUNDED
Purple & Tan = 12V

KEY ON OIL TANK SENSOR GROUNDED
Purple & Tan = 12V

KEY ON VRO SENSOR GROUNDED
Couldn't test, wasn't sure which of the 3 pins to use

KEY ON FUEL RESTRICTION GROUNDED
Couldn't find in the service manual how to test, seems to matter only at WOT anyway

The 3V with just KEY on had me confused, but I pretty much expect that I could hook up any 12V buzzer to Purple & Tan, and the new buzzer should work for the various sensor tests. I got a 2 wire piezo buzzer that is only supposed to work on 6V-24V, problem is that even with the 3V present during just KEY ON, it would buzz, although not that loud. So that wasn't going to work, and was about to find another buzzer or break down and buy the correct one.

So while it was buzzing with just KEY ON, I unplugged just the OIL TANK SENSOR, still buzzing (3V). Unplugged just the VRO SENSOR, still buzzing (3V). Unplugged both and buzzing stopped, and voltage was now was now 0 between Purple and Tan.

Easy to imagine the OIL TANK SENSOR might be bad, but also the VRO SENSOR too? Anyhow, I had planned on disabling the VRO, which I have now done, so no need to worry about those two. Still bothers me though, since I don't understand what is going on.

The other weird thing is that if the faulty stock buzzer is removed entirely from the circuit, I get 12V between Purple and Tan with KEY ON no matter what, so I have to leave it in place, and just parallel the new buzzer on top of it.

And I could not find in the service manual if my system should beep once when turning the key on, but it currently doesn't do that.

Sorry for the long winded post, but it is certainly better than it was before, and hope I haven't missed something.

 

[Will Bark]

If your buzzer is bad you can do what I did which is to get a $10.00 back-up horn from Auto-Zone and mount it externally; works fine for 5 years with no problem. Good luck