Mercury clean power question

[willymac]

3B460301 250 ProXS

My clean power is connected directly to battery. My engine is connected through a cutoff switch. When switch is in off position, if the key is turned on or trim switch is bumped, it will blow clean power fuse.

I just repowered yesterday, and this could get aggravating and possibly damage pcm everytime my kids get in the boat in the shop, as it seems it is trying to power accessories through the clean power circuit.

Questions are is this normal, and if so, why is it recommended to have engine on switch but clean power not? I understand Mercury's stance on clean power is to be connected to battery directly, but would it adversely affect engine to have clean power on its own switch away from other loads to prevent this issue?

[Another Distraction]

That's not normal and "clean" power's Pos and Neg MUST go from back of motor directly to battery or from J box directly to battery. We've all questioned this but it must be done.

Does your clean power fuse blow if you leave battery switch OFF and then tilt engine using the button on the side of the motor? If it does then disconnect the 14 pin harness from the back of the motor and try tilting motor again using the same switch on side of motor.

Is the 14 pin harness and outboard motor brand spanking new?

[willymac]

Key off, battery cutoff switch off - clean power fuse blew when trying to operate engine mounted trim.

Key off, battery cutoff switch off, 14 pin disconnected at back of motor- clean power fuse did not blow when operating engine mounted trim switch. Trim did not operate of course, but I could hear the trim solenoid clicking.

Boat was repowered this week, engine has 4 flawless hours on it. Clean power harness looks to be installed correctly from the battery to the back of engine next to 14 pin harness. 14 pin harness is original to the boat with an extension I believe. I don't see anything out of the ordinary on install.

[Another Distraction]

You used the words engine mounted trim twice. I think one of those should say throttle or dash mounted trim switch. Right?

[willymac]

Sorry, I edited my post. The second test was with 14 pin at motor disconnected.

[Another Distraction]

"Key off, battery cutoff switch off, 14 pin disconnected at back of motor- clean power fuse did not blow when operating engine mounted trim switch. Trim did not operate of course, but I could hear the trim solenoid clicking."

Thinking you shouldn't have heard the trim solenoid clicking. Pull the fuse OUT of the clean power cable and do the above again. Let me know if you still hear the relay "clicking".

[willymac]

"Key off, battery cutoff switch off, 14 pin disconnected at back of motor- clean power fuse did not blow when operating engine mounted trim switch. Trim did not operate of course, but I could hear the trim solenoid clicking."

Thinking you shouldn't have heard the trim solenoid clicking. Pull the fuse OUT of the clean power cable and do the above again. Let me know if you still hear the relay "clicking".

Key off, battery cutoff off, 14 pin at rear of engine disconnected, and clean power fuse removed - no solenoid click when pushing engine mounted trim switches, replaced fuse only from above, faint click of solenoid when engine mounted trim switches are pressed.

[EuropeanAM]

AnotherDistraction- you've gotten off the topic on this one.

IF the engine is rigged through a battery cutoff switch, Clean power directly to battery (which is REQUIRED), and the operator fails to turn the battery switch to the ON position before grabbing the key swtich: It often will blow the clean power fuse (which is protecting engine circuits from an over-current situation).

Simply remember to turn on the switch. If you forget, it will remind you as you replace the fuse.

[Another Distraction]

If you're saying Mercury's PCM allows the 5 amp, tiny wire gauge, clean power harness to solely power the starter or trim motor, it should blow every single time.

I can't believe Mercury ran a second power line to the PCM and would allow it to power huge loads leaving you stuck on land or adrift in the ocean. It doesn't sound right.

Mercury should give out breakers rather than fuses! lol.....

[EuropeanAM]

Or perhaps... if an operator has a battery disconnect switch, he should remember to turn it ON before inserting the key.

Just a suggestion, of course. Not the first thing we have to remember with a boat (bildge plug, fuel, charge batteries, etc). And it's not attempting to power the starter.

[willymac]

Or perhaps... if an operator has a battery disconnect switch, he should remember to turn it ON before inserting the key.

Just a suggestion, of course. Not the first thing we have to remember with a boat (bildge plug, fuel, charge batteries, etc). And it's not attempting to power the starter.

I understand how I blew the fuse, question was, is that normal, and you answered my question that it is.

My concern is, I like to completely disconnect power on my boat while in tow and storage in my shop. My key is not left in the ignition, but if my kids bump the trim switch while playing in the boat, it will blow the fuse. I guess my only option is to pull clean power fuse when I want to isolate all power. The con to that is the repeated pulling and installing fuse will eventually loosen the fuse socket and will lead to poor connection which defeats the purpose of a dedicated, strsight battery connection clean power harness.

[EuropeanAM]

I understand your situation. Don't think I haven't seen them run to the battery shutoff switch... because I have. And it works- BUT there are some important safety concerns if there are any abnormalities in that switching circuit (clean power is in place to ensure a crystal-clear connection direct to the cranking battery, with as little interference from other high-amperage or high-load devices as possible). Think about the Electronic Throttle and Shift systems involved and how critical being able to keep the PCM up and awake would be.

[willymac]

No I do understand the importance of it. I guess I'm just venting more than anything, especially since it has been confirmed that it is normal behavior of the system. I'll just have to deal with it.

[Another Distraction]

5 amp breaker.jpg​

[EuropeanAM]

Work: Yes.

I'd have to see test comparisons before I would install one, myself. Fuse is either good or not good, circuit breakers can be intermittent (which is real bad).

[bellaireroad]

What is pulling a big enough load to blow the clean power fuse when the switch is turned off? I was under the impression that it only powered the ECM, but I guess that was wrong

[EuropeanAM]

As long as no-one attempts to turn the key on, start the engine, or PERHAPS operate the trim, that would normally be correct.

[bbqpitboss]

Not to hijack the thread but if my cutoff switch is off and I bump the trim at the console or motor my fuse does not blow. Do I have a problem?

[JohnnyGZ21]

[EuropeanAM]

Not to hijack the thread but if my cutoff switch is off and I bump the trim at the console or motor my fuse does not blow. Do I have a problem?

No.