SOLVED: Engine Turns over when i hit the horn and others

[joeyr]

hi All,
i recently had a mercruiser engine replaced with an OMC engine both were Gm 165 inline 6 (from the 70's)
Engine looked near indentical
When I got it back from the boat place (long story) my boat engine would no longer be turned over with the key - pushing the horn turned the engine over even in gear. I am educated in electronics at the college level so i took a look at the wiring - the horn is still wired to the horn - no shorts under the dash. Also if you turn on the NAV lights the engine turns over.
I've isolated every circuit under the dash by cutting them out with no luck.

Any suggestions?

PS - if the key is on and i push the horn the engine starts and runs well.

 

[cooter2506]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

Did they p*ss you off and then they got you back, lol. Sorry had to say it. Personally I would take it back to them and tell them to fix at N/C. That is if they were the ones to set and wire engine.

 

[flargin]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

PS - if the key is on and i push the horn the engine starts and runs well.

Ok, had to say, this really made me laugh... ... I know you are hurting, but I had to let you know.

When I got it back from the boat place (long story)

I have to imagine, this precludes you from taking it back to them and say "FIX IT"

I have a feeling the return side of the horn switch (one side will be fed from the Red/Purple line (+12v)), is connected at some method to the Yellow/Red starting circuit. This will be post the shift linkage.

What I think is happening, is when you push the horn button, the horn goes, and the rest of the circuit goes down the starter and activates the starting circuit.

I would check the color codes for your ignition wires first. pictures might help.

Does this have a standard "Engine coupler" i.e.

If so, you can isolate if the problem is in the front or on the engine (but my guess is it is up front)

 

[joeyr]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

ya it is a standard engine coupler.

I have to also mention when I turn the key i blow a fuse

I'm trying to avoid bringing it back to them... all they have to say is: "oh you need a new wire harness" or some bull **** that I would have to buy. When really i want to REAL reason for changing another expensive part

I cut the ignition circuit out, push the horn and it turns over. I have a direct 12v+ wire coming from the battery, touched it on proper lead for the horn, and the engine turns over!

 

[ziggy]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

hum, while i'm not college educated in electronics. i think i can read a wiring diagram. the one for the 165hp L6 is not horrible complicated looking. this is where i'd start. then i'd go to the boat and see if it's wired per the diagram. obviously it's not. the horn, nav. lights, any acc. should have nothing to do with the operation of the engine. myself. i had a few acc. on my boat that were wired into the engine circuits. i removed them and put in a aftermarket fuse panel and ran all acc. to that. in your case. i think i'd try to start separating out the engine circuits from the acc. circuits.. then go make the engine circuits match the wiring diagram in the book... put it back to oem specs.
the horn circuits is about as simple as it gets for wiring. nothing more than 2 wires a horn and a switch. all hooked up in series. any extra wires gots to go somewhere else. likely over to the ign. switch in your case i'd think. who knows where the wires from your ign. switch go. turning the key to start condition should not cause a short. nav lights aren't much more complicated, it just has a double throw switch i think it's called so your able to energize the stern light or both stern light and bow lights. still one wire feeding the switch, one wire ea. going to the stern light, one going to the bow light then off to ground.

to me this sounds like some kind of engineering to overcome a bad ign. switch. it needs to go back to the way the oem did it..

i'd not take it back to whoever did that work. they seem to have no clue and i wouldn't let them touch my boat again. imho..

hopefully ya got the service manual. your gonna need it i think.. no idea if the links in the adults only thread still work. but i'd sure go and try if ya ain't hip to the book. if they don't work, get the book. the service manual is the best tool you'll have in your toolbox..

 

[bruceb58]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

I have a feeling the ground side of the horn switch (one side will be fed from the Red/Purple line (+12v)), is connected at some method to the Yellow/Red starting circuit.

First of all...the horn switch does not switch ground. There is no ground side to the horn switch.

What I would do is to trace the wire from the solenoid to the neutral safety switch in your controller and then trace the wire from the other side of the neutral switch to where it goes in your dash. If you want you can use a meter that has a continuity beeper. You must disconnect it from the solenoid first and attach one end of the meter to that wire. You might need a long test lead with alligator clips at both ends. You can make one yourself.

 

[flargin]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

the start blows a fuse makes sense.

there is likely a common return which has been tapped into the starting circuit.

I would take apart your coupling, and see if it is motor side.

on my mercruiser (and it may be the same as yours)
+ 12V = Red/Purple = pin 6.
Run/Ignition on = Purple = Pin 5
Starter = Yellow/Red = Pin 7.

You can turn on the motor by jumping a wire between 6 and 5. You can run your starter by jumping a wire between 6 and 7.

If you blow the fuse there, your problem may be near the motor. if it works, it is up front.

I have a feeling your problem is up front, and if it is we should move this to the electronics thread, but as ziggy said, first is to drive to be 'oem'.

The other chance is an erroneous screw has speared some wires in a wire harness between the front and the back.

 

[bruceb58]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

there is likely a common ground comming down your switches, which has been tapped into the starting circuit.

This is not a grounding problem! The solenoid gets its ground through the block.

He needs to trace the wire.

 

[spktho]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

First of all...the horn switch does not switch ground. There is no ground side to the horn switch.

What I would do is to trace the wire from the solenoid to the neutral safety switch in your controller and then trace the wire from the other side of the neutral switch to where it goes in your dash. If you want you can use a meter that has a continuity beeper. You must disconnect it from the solenoid first and attach one end of the meter to that wire. You might need a long test lead with alligator clips at both ends. You can make one yourself.

^^^isolate the starting circuit first.

 

[flargin]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

This is not a grounding problem! The solenoid gets its ground through the block.

He needs to trace the wire.

I agree this is not a grounding, but there is some +12v getting applied to the starting wire from some location, my thought is there is some other 12v circuit that has been shorted over to the starting wire, applying +12 to the starting wire.

Since there are a couple of independent circuits causing the problems, then normally you find the gremlins on the return legs, which I called ground.

I will edit the comment to read:
I have a feeling the return side of the horn switch (one side will be fed from the Red/Purple line (+12v)), is connected at some method to the Yellow/Red starting circuit

Thanks for

 

[bruceb58]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

Sorry...I am an electrical engineer and think it is important to get the terminology correct so there is less confusion. For a switched circuit, there is the switched side of the circuit and the unswitched side of the circuit. The unswitched side of the switch is the 12V and the switched side of the circuit goes to the horn.


If you really think there is a short between the start wire at the ignition switch and the starter solenoid, just remove the start wire from the ignition switch and then push the horn button and see if it still starts. Still need to trace the wire all the way.

 

[bruceb58]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

^^^isolate the starting circuit first.

By removing the one end he is isolating the circuit enough to do the continuity check.

 

[bruceb58]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

I am re-reading this thread. Which fuse blows when you turn the ignition switch to on or is it when you turn the key to the start position?

 

[flargin]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

Bruce, I appreciate your passion, I have it too. I try to use the correct terms too. Ground is a difficult word, especially on a boat. Mercury calls all their black wires "ground", so it is somewhat of a logistical mess.

 

[joeyr]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

Hey Guys,

Thanks for all the info... it's late and I have not applied any of the techniques you've described yet.
What I have done:
I have a stereo system I installed last year, which has it's own circuit to the battery. The "ground" wire was close by so I attached it the the existing ground under the dash. The horn now works normally with the new "ground" attached. the key still does not turn over the engine and still blows a fuse.

I will try removing the harness tomorrow and apply some of the techniques and advise everyone has given, and i will post the results.
I have a feeling it has to do with the merc engine being replaced with the OMC engine but not the wire harness being a merc... we will see soon enough

 

[joeyr]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

I forgot to mention - the fuse only blow when attempting to turn over the engine
When the key is in the on position I took a voiltage reading of the accessories that are lit up and onlt get 5.something volts. and when attaching my "bypass ground" I get the full 12.5 ish.

 

[joeyr]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

It looks like it has something to do with the wire harness coupler. After testing the wires with a meter, the wires don;t match the config it should be.

I must find some kind of Merc boat harness to OMC engine config

 

[bds85466]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

which brings up a good point: don't let crackheads work on your boat. Those guys screwed you royally.

 

[legoman67]

Re: Engine Turns over when i hit the horn and others

Re: Engine Turns over when i hit the horn and others

the older carburated engines are pretty simple to wire, i can wire an engine in about 20 minutes.

check these wires.

- from positive on the coil, to 'run' position on the ignition
- from one of the small ports on the solinoid(yellow, or red wire) to the 'start' position on the ignition(the other small terminal should be grounded)
- from the negative on the coil, to 'S' on the tach
- from each sensor, to the corresponding 'S' on the gauge.

if you want directed unprotected power to the helm you should tap off the main positive entering the starter, make sure someone isnt tapping off the small terminals..

 

[joeyr]

SOLVED: Engine Turns over when i hit the horn and others

SOLVED: Engine Turns over when i hit the horn and others

Well I figured it out. It was the wire harness coupler. It was setup that the ground was going the my key switch (ignition) and the igntion was going to ground. Oddly enough all the others matched (for the numerous gauges I have)

Drove the boat all weekend runs really nice and quiet with my new OMC 165.