Odd temp horn issue

fsds123

Petty Officer 2nd Class
Joined
Apr 8, 2003
Messages
142
1979 115hp Evinrude. The previous owner had disconnected the temp horn at the controls...noticed this when installing a new console. Hooked it up and got the following:

Started motor and the horn buzzes immediately and stays on. Killed motor and put key in on position and grounded wires leading to temp sensors...and got sparks. Both wires leading to the temp sensors are getting 12v with the key in the on position.

So 2 strange issues...

1. I am getting 12v to the temp sensor wires.
2. Horn sounding only when engine is running, but not when key is in on position.

Any ideas?
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: Odd temp horn issue

You should get 12 volts on the control side of the tan wires.

The horn should be wired to receive positive voltage directly from the ignition switch' positive accessories post "A" by a purple wire.

The tan ground wire should run through the main harness to the temperature switches on the cylinder heads.

The horn should not sound unless the tan wire is in fact grounded, so disconnect the temp sensors and see if that stops the horn. If it does not stop, you have a short to ground somewhere on the tan wire. You should find quick disconnects a few inches from the cylinder heads; slide the cover back.
 

fsds123

Petty Officer 2nd Class
Joined
Apr 8, 2003
Messages
142
Re: Odd temp horn issue

The horn sounds even with both temp sensors unplugged, (but only when engine is running, not when key is just in on position) and the tan wires going to the sensors show 12v when key is in on position.
 

ezeke

Supreme Mariner
Joined
Sep 19, 2003
Messages
12,532
Re: Odd temp horn issue

Accessory voltage from the ignition switch is only ON when the ignition switch is in run or start position, so the horn has no voltage in the off position which is correct.

There should be no connection between the running of the engine and whether or not the horn works since the ignition system is not connected to the harness wiring except indirectly through the rectifier. You may have a burned blocking diode. Did you clean the connections in the large red plug at the engine?
 

fsds123

Petty Officer 2nd Class
Joined
Apr 8, 2003
Messages
142
Re: Odd temp horn issue

I found the problem. I traced the tan wire back further looking for a short...only to notice the tan wire turning into a gray wire. Looks like the previous owner used whatever color wire he had laying around to hook up his tach. Found the correct tan wire and now the horns work as they should. Makes sense now why the horn was going off only with the engine running...
 

fsds123

Petty Officer 2nd Class
Joined
Apr 8, 2003
Messages
142
Re: Odd temp horn issue

Great, just as i think the boat is all done I try to start it. Nothing. Blown fuse. Put in new fuse, and it now cranks, but no spark.
 
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