no voltage to temp sensor wire

[mutron77]

Hello<br />Over heat horn will not sound during ground test.<br />After inquiring on the forum I was told that there should be 12V to the harness side of the tan wires that lead to the head temp sensors when the key is in the on position. I did this test with my fluke and no voltage. The tan wire that ran to the VRO tank has been disconnected (bypass in progress).<br />Where should I look next to troubleshoot this? The console is an '85 w/ an '85 EV 90 with the key slot tester. Inserting the key also has no effect. Should I next pull the shift console and check the wiring in there or is there a fuse somewhere that may be blown. I know that the horn fuse is missing, but that is not located near the shift console. When my mechanic friend tried the key slot test using a screw driver blade (with the key on) there was a spark and the 20 amp crank fuse blew in the engine. I replaced that and the engine now cranks.<br />Could disconnecting the branch that went to the VRO have anything to do with it? any Ideas?<br />Also, if all was working could I test the sensors themselves using a heat gun to warm up the sensor in the head? Or how can these be tested?<br /><br />H90

 

[Hooty]

Re: no voltage to temp sensor wire

There's not suppose to be 12vdc going to the high temp sensor. The tan wire is the groung wire to the warning horn. When the high temp switch reaches 180*, it closes and completes the ground circuit to the horn and it sings. <br /><br />c/6<br />Hooty

 

[mutron77]

Re: no voltage to temp sensor wire

Hmmm.... that makes sense. Here is what someone posted in a previous thread<br /><br />---------------------<br />"you should also have 12v on the tan wire that goes to that same overheat thermo if the horn is good and it has 12v on it and the wire back to motor is not cut."<br /><br />-------------------------------------------<br />Is this just wrong or is there something I'm missing between the lines?<br /><br />H90

 

[Trent]

Re: no voltage to temp sensor wire

Hooty is right on. Grounding the tan wire completes the circuit to the horn.

 

[kgw]

Re: no voltage to temp sensor wire

Hi guys,<br />My 140 schemaatic and in tracing circuit on my boat the horn has 12v applied at key on the 12v travels through the horn via tan wire to the overheat sensor and when the sensor closes and completes the circuit to ground the horn sounds.Therefore there is 12v to the sensor at key on. if the sensor is in an open state. but I do not have a self test horn. dont know if he does.

 

[mutron77]

Re: no voltage to temp sensor wire

No it's not a self test. It just has the key slot tester.

 

[kgw]

Re: no voltage to temp sensor wire

horse90,<br />then you should have approx. 12v or maybe 10v allowing for voltage drop across the horn. to the over heat sensor in the head thats the only way the circuit can work.<br /> good luck.

 

[Hooty]

Re: no voltage to temp sensor wire

The sensor is a N.O. set of contacts that, on temperature rise, close and complete the ground circuit to the alarm. The alarm does have 12vdc from the switch to one side, not the sensor.<br /><br />c/6<br />Hooty

 

[rodbolt]

Re: no voltage to temp sensor wire

hello<br /> volts dont travel<br /> current travels.<br /> when the key switch is on you will have 12 volts at the tan wire disconect if the system is working. the themo switch is a normally open wax pellet switch.<br /> if the motor in question is pre system check it uses 12 volts on all tan wires. system check and most post 95 models that have tan wires with black,yellow orange or other tracers use a 5 volt circuit for system check. anyway getting back to the circuit on a pre 95 jonny/rude. when the key switch is turned on it applies a voltage to the alarm horn,if its a self test horn as the circuits work it allows current to momentarily flow through the horn circuits to self test the audible, if its the old style it is just a coil of wires. so now we have 12 volts on the purple wire,12 volts on the tan wire{assuming the horn is functioning} now we have 12 volts sitting anywhere the tan wires are connected.if you close the circuit you now lose 12 volts cause you made a current path.so KGW almost wins. he just has to quit thinking of voltage flowing. volts dont flow. but I have to ask. what is a key slot test? that one is puzzling me. never heard of that one but the list of stuff I never heard of grows longer everyday. anyway. if you disconnect the tan wire at the temp sensor and turn the key on you should have a 12 volt reading at the connector to ground. if you dont try the tan wire at the horn to ground. if you still dont go to the purple wire at the horn to ground. if you now have 12 volts your horn is bad, if you dont fix the wire between the horn and the key swtch.<br /> good luck and keep posting<br />PS please tell me what a key slot test is<br /> I gotta know

 

[ob]

Re: no voltage to temp sensor wire

Rodbolt,On early model side mount controls ,if you lift the fast idle lever ,there is a slotted hole to test the alarm horn with the key in the "on" position.The keyslot enables a suitable piece of metal(key) to be inserted which completes the circuit to the horn for test.<br /><br />And,I just checked my 96' model for grins and there is indeed 12 volts present at the tan wire exiting the temp sensor when the key is in the "on" position.<br /><br />BTW,Very good explanation of the temp sensor circuit function Rodbolt.I learned something.

 

[kgw]

Re: no voltage to temp sensor wire

HI Rodbolt,<br /> I know there is no current "flowing" but for all practicle purposes the potetial is there for it to flow ,hense the 12 or 10v is there to measure with a meter. <br /> thanks for the explanation I can now sleep tonight knowing I have not forgot how to read a schematic after using them for 40yrs.

 

[Joe Reeves]

Re: no voltage to temp sensor wire

Horse90..... Did you find the problem with the warning horn?

 

[mutron77]

Re: no voltage to temp sensor wire

Hi Joe,<br /><br />Update, pulled the console and split the halves.<br />The horn (hockey puck looking thing). Appears to be shorted to the point that the case was melting in the process. Is this what happens when these things fail, or may I have another problem that caused this? The lead wires are fine and the purple one does have battery voltage with the key on. Here are some pics for everyone's info.<br />To remove the console on an '85 like mine, Remove the 2 long through mounting bolts, nuts, and washers. The box will drop off. Turn it face down and remove the three phillips screws on back. Gently coax it apart. On mine it was Not necessary to remove the shifter (allen bolt) or the fast idle lever.<br />H90<br /><br /> <br />

 

[kgw]

Re: no voltage to temp sensor wire

Well horse looks like you found your problem, the same thing happend to my horn right after I bought it in 1986<br />P.S. i think the horn failed because whoever set the boat up tapped a hour meter to the tan wire after the horn

 

[mutron77]

Re: no voltage to temp sensor wire

kgw,<br /><br />Yours melted like that too? I wonder how much for a new one. Actually had this horn go off 5 years ago at the lake. The marine shop replaced some water deflectors or something in the heads, but maybe that was when the horn decided to short and melt, and that was its death toot....<br /><br />H90

 

[kgw]

Re: no voltage to temp sensor wire

Yes horse, melted just like yours.Cant remember the cost. God that was 18yrs ago .<br />glad you found it.