constant alarm on cold motor with key on

Just put new powerhead on 1989 omc seadrive (1.6 ltr 140 hp same as Johnson Evinrude) also put new control box and harness from box to transom, pretty much plug and play. Even if I unplug the sensors on the heads and the vro pump lead, still constant horn . All these wires are tan.
Please I am really stuck on this and don't want to run this new unit with no alarm. Thanks in advance for any help, advice or hints you can supply.

 

No disrespect, but sometimes the obvious is the answer. You said you don't want to run it, and your topic heading says horn sounds with the key on. Have you started it?

Protect the engine by mixing OB oil in your gas tank at the ratio (probably 50-1) stated in your manual. This will allow you to run it safely in case the vro pump is bad or a line blocked. If you're fortunate, the alarm will stop after a few seconds.

It could also be a case of needing to prime the vro pump and/or the fuel pump. Disconnect the line from the oil tank to the vro pump and squeeze the bulb, using a container to catch the oil, watching for air bubbles. Reconnect when you have a steady stream. Do the same for the fuel line.

One other thought. Has the water pump been rebuilt recently?

 

Thanks Charlie, I did drive it a couple miles to my dock space with the horn sounding, the water pump I did with the powerhead as well as thermostats, I think I have a grounded wire somewhere in one of the harnesses because the horn sounds even with all sensors unpluged , I am running a 50:1 mix as part of the breakin procedure if you can think of anything else Im all ears
Thanks

 

Just a wild guess, but maybe you need to reverse the leads to the horn button so that the horn grounds at the button rather than feeding voltage to the horn. The horn button may need to ground rather than feed.
So from the horn fuse, bypass the button and go hot directly to the terminal on the horn, and then tie the sensor wire to the ground wire from the horn, and then ground the other button terminal.
The sensor wire is probably tied into the grounding circuit now. The horn should only ground after the horn button doing it this way, and I can't see any other way it would work anyway.

Alan

 

I tend to agree with Tim that it's likely an electrical problem, particularly since it runs OK (fuel) and didn't overheat when you ran it after replacing water pump and t-stat.

Here are some links that might help:

http://www.outboardmotor.biz/t/013855.html

http://www.outboardmotor.biz/t/005416.html

 

The temp sensor is a small rubbery thing in the cylinder head. Disconnect it,--if it still blows you have an earth from the horn.