Johnson 40hp temp switch

[Maverick49]

I have a 1990 40hp Johnson, I get a constant warning horn buzz with with the key on, I was told the horns do go bad, also to check the pee hose to see if it's shooting water and if it's hot to the touch, and to also see if I could put my hand on the cylinder head and not get burned, So I changed the warning horn to a new one, and still I get the buzz with the key on, and the water coming out of the pee hose is cold, and I can put my hand on the head and not get burned but it is very warm, so I took out the temp switch and have tested it according to my OMC manual page 4-7 and the switch opens up about 180 degrees but will not close even when the temp of the oil gets up to 230 degrees, the book says the switch must react to the changing temperature and to replace the switch if my results vary. Do I need a new temp switch?

 

[R.Johnson]

Re: Johnson 40hp temp switch

The switch goes closed at 180, and will stay closed until a drop in temp., not a rise.

 

[Walker]

Re: Johnson 40hp temp switch

Make sure the tan wire from the temp switch doeswn't have any bare spots touching the motor. Then follow the wire from the temp switch til you find the plug. Unplug the wire and see that kills the alarm. If so then you need a new switch. If not then your problem is not in the switch.

 

[Maverick49]

Re: Johnson 40hp temp switch

I've done like the manual says, the horn comes on as soon as I turn the key switch to the on position. and when I unplug the bullet connector to the temp switch and ground it like the manual says and I get a louder buzz.

 

[R.Johnson]

Re: Johnson 40hp temp switch

When you touch the sensor wire to ground, and the horn get's louder make's me think that horn is picking up a partial ground some where. Disconnect the tan lead at both end's, hook an ohm meter to the horn end, and to ground, see if you get a reading. If not, you could well have a defective horn.

 

[Maverick49]

Re: Johnson 40hp temp switch

I have just purchased a new horn, thinking my old one was defective, so I unhook the tan wire from the temp switch and tan from the horn and use an ohm meter on both ends or just the horn end and ground the other lead from my meter?

 

[R.Johnson]

Re: Johnson 40hp temp switch

Yes, hook to horn end, other lead to engine block.

 

[Maverick49]

Re: Johnson 40hp temp switch

I hooked the red lead of my ohm meter to the tan wire that plugs into the horn and then I touch the black lead of my ohm meter to a ground on the engine block with the ohm meter set to ohm's & I get 1.545 readout on the meter. I'm sorry if this sounds kinda basic, account I didn't pay attention in class 32 years ago when we were learning ohm's & voltage & that stuff I'd be needing to know later in life.

 

[gejandsons]

Re: Johnson 40hp temp switch

Unplug the heat sensor/switch & see if it is still a dead short. If so the sensor is bad, If not the wire has a leak. The switch goes to a dead short after reaching a predetermined temperature to complete the circuit to make the warning horn sound off for overheating. Is it oil injected?

 

[Maverick49]

Re: Johnson 40hp temp switch

Like I said earlier, I have a constant alarm from my warning horn with the key switch turned on. so if I unplug the temp sensor and ground it out I already have the alarm going off, so I cant tell if it is going to make my alarm sound or not. I have unplugged the VRO wiring harness and the tan wire and I do not get the alarm, so then I can unplug my temp switch and ground it out like the manual says and it will make the alarm sound, this makes me think that I have a wiring harness problem with my vro, but it does pump oil to the motor I can visually see the oil level drop. So I went to the lake, I mixed my gas with 50 to 1 I ran it for 15 to 20 minutes with both the VRO oil injection hooked up and my gas premixed, then I stopped the motor unplugged the wiring harness to the vro along with the tan wire, and started the motor and no alarm then I unplugged the temp switch and grounded it out like the manual says to do and the alarm then buzzed as it is suppose to do. Am I wrong thinking that it's in the electrical harness for the vro? I'm ready to pull the oil hose to the motor and just run the premix, it's the only way the warning horn will not emit the ear peircing sound.

 

[gejandsons]

Re: Johnson 40hp temp switch

Check the temp sensor for a dead short with a multimeter. Don't ground it to block. Block to the tan wire that is connected to the temp sensor should give you an open reading . Something has the horn grounded causing it to blow.

Unplugging the temp sensor with the horn sounding proves it is not a faulty sensor if the horn continues to blow. If disconnecting the VRO tan wire stops the horn, then it is in one of the VRO switches or a bare wire on the VRO grounded out.

 

[gejandsons]

Re: Johnson 40hp temp switch

If you old horn was blowing then it is not bad.