alarm driving me crazy

[mississippiriverrat]

new to iboats and boating. wanted to say you guys are great and i have learned a lot just by reading in the forums. I bought a used mercury out board ser. # OB383808 it is suposed to be a 200 hp black max went through cooling system and replaced the thermostats popit valve and water pump rebuilt carbs and changed lube in lower unit. but i am still getting a over heat alarm when running above a good fast idol. pressure gauge seems to be working right 5 to 8 psi at idol and goes up to about 18 psi at 2800 then drops after popit opens pulled sending units on the heads but need to know if these are both overheat alarms or is one for the temp gauge both have airpac on them but differnt numbers one is 9751 and the other is 9919. they are both wired to the same terminal block and go to the alarm horn. is this right or is there something wired wrong i got a manuel from libiary but could not make heads or tails from the wiring charts. would like to get this fixed the cats are starting to bite

 

[JUSTINTIME]

Re: alarm driving me crazy

tan or tan blue is over heat
blue is oil
u need to take the manual home and trace wires

 

[mississippiriverrat]

Re: alarm driving me crazy

both wires are tan w blue stripe i understand what wire colors mean what i could not find stated anywhere is if these are both overheat switches or is one a temp. sending unit

 

[JUSTINTIME]

Re: alarm driving me crazy

over heat is usally highest on the block

 

[mississippiriverrat]

Re: alarm driving me crazy

they are both betwen the top two plugs on both heads small silver buttons held in with a clamp like the old distributers

 

[Texasmark]

Re: alarm driving me crazy

You have the right baby; temp sensors. Wiring is correct. If both are blue tan then over the years, someone had a failure on the port side and replaced it with a starboard sensor which is blue tan......no biggie.

The sensors are wired in parallel so one can be bad....just had a problem with them on son's 150. He has the light and audible alarm. They were both on but dim all the time. An ohmmeter check of the port sensor revealed about 90 ohms of resistance between the case of it and the terminal.....it should be open till you hit 195F (on our engines). Removing it from the engine block cured the problem. New one is on order.

Mark