90hp mercury fuse/rectifier problem

[georgia088]

I have a 2003 90hp mercury outboard 2 stroke It has always ran perfect. A few weeks ago I blew main 20 amp fuse that’s under cowl. When it’s blown it will not turn Ignition on or crank. I traced every wire back and can not find a short anywhere. It only blows the fuse at WOT (5500-6000 rpms) I can ride all day long below this rpm with no problem. I have turned the key on and moved the throttle in every possible position and it will not blow fuse. I have wiggled every wire while running and it won t blow fuse.

I decided it must be the rectifier allowing to many amps causing the fuse to blow. I replaced the rectifier. I still blew fuse. Put another fuse in and now I am pretty sure I’ve blown the new rectifier. (no tach and voltage lower than 12v when running boat). When this happened the fuse didn’t blow. Any ideas? Only other thing I can think of is stator? But wouldn’t the boat run bad if the stator was bad/going bad? Thanks for any help!

 

[Texasmark]

Red line on that engine is 5500. I had a 2002 and when running WOT, I ran 57-5800 and one time I was diddling the timing in the driveway and it pegged the 7k tach for maybe 30 seconds before I could get it turned off. Didn't blow the fuse.

Stator runs the battery charger (yellow wires) and trigger circuit HV capacitor chargers ( green white and white green on 1998 and newer engines) yellow is less than a hundred volts AC and the other 300-400v. The circuits are independent of each other, coils of wire.

If your battery is sitting at 12v, it is either discharged or under a higher load than the regulator rectifier can deliver...red stator 16 amps and black 9. With a fully charged battery and low amperage load, it can run up to 14.5V. Running at moderate or higher throttle, with boom box or suitable load will pull it down to around 13....always higher than the voltage measured across the terminals with the engine is off.

First thing I would suspect is a dead cell in the battery. Take it to an auto parts store and have it load checked.
-----------------
The Stator yellow wires feed the reg-rect module, output of which is connected to the input terminal of the starting solenoid....B+ voltage distribution point. The battery is connected to that point also as it and the regulator obviously supply power to all the engine and auxiliary circuits. Power to the two trim relays "to run the motor" also comes off that stud, not in the fused circuit.

The fused circuit feeds power to the "trim control coils" in the trim relays (low current) and goes out on the remote wiring harness to the control box for operating the ignition switch functions and aux lighting circuits or other accessories not on "switched power".
---------------
When you are running at WOT, are you on your trim button constantly? If so, swap trim relays, replace your fuse, get the battery good or bad question answered, and test it........Test the battery voltage without the engine running, Start the engine, run up to 1500 RPM, all accessories off, and see if the voltage exceeds the off voltage. If so fine on the regulator. If not, back after that. Run the trim up and down a few times, max up to max down. Fuse blow?

Will check back for your answers.

 

[georgia088]

I put old rectifier back in and it definitely is putting out voltage while running...(any where from 12.5-14.1v depending on how many rpms) I apparently fried the new one I just put in. However, the old one still blows the fuse if I run at wot. I haven’t touched the trim at all during wot run and it still blows fuse. I tried To trim it up and down to the maxes a million times to try and make the fuse blow with the trim but it doesn’t. I don’t think it’s the trim.
the battery is about two years old, so that is a possibility, but would a bad cell only cause the fuse to blow at wot? Thanks for the help!

 

[Texasmark]

Alternator is putting out max voltage, and current. Differential voltage at battery would be the highest, so for a given resistance, the current requirement would be max. I'd get the battery out of the equation and go from there. Sounds like the rest of it is ok.

Terminals where the fuse mounts aren't corroded are they? Corrosion would amount to a resistance and at high currents, Ohms law could account for added heat at the fuse making it think it had a circuit overload with the level of heat and it blows.

What does the fuel look like where it blows. Does it look like it exploded, or does it look like it just melted and the circuit opened?

 

[georgia088]

I would say the fuse looks like it just melted. It appears to be a clean break in the fuse. The “fuse holder” doesn’t look corroded to me. The connections to the rectifier are slightly corroded but nothing that would draw attention. I tried cleaning them the best I could.
I ran it with the cover off today and I did notice the wires going to the fuse holder were hot before the fuse blew... but obviously this is happening or the fuse wouldn’t blow. I have a new battery to go in it. I will rule that out, but it will be the weekend at the earliest. Is there no way it could be the stator? Obviously, I hope not, but I just can’t imagine what else it could be.

 

[Faztbullet]

Sap to a different batery and test and also check resistance on keyswitch

 

[sam am I]

Is there no way it could be the stator? Obviously, I hope not, but I just can’t imagine what else it could be.

More $.02.......

Typically not failing in such a way to blow the 20 amp main motor fuse, even the coil shorting to ground or shorted wingings shouldn't blow your 20 amp main fuse, the rec/reg's (a good one) diodes prevent current flow backwards from the directly (*no fuse) connected battery, so no not that I can think of however!! Anything is possible I reckon but i hate guessing, so.....

You can of course test your theory and eliminate the possibility by dis-connecting it and running without it. Just unplug/secure the yellow wires and go crazy WOT! Running w/o the charge coil connected is perfectly safe on the motor/stator.

I'm a bit perplexed on the rec/reg that blew up though.........I'm sorta scratching my head on this one still, and again, that rec/reg could have its input (the charging winding of the stator) shorting to ground, shorting windings and the like and still shouldn't fry like you've reported.........They fry (over time usually) however running too hot, i.e. large loads that pull lots of current.

A s**t battery c/would certainly do this. BUT, why does the old rec/reg still work? Is it getting hot to the touch? Perhaps the new rec/reg that fried was a cheep knock off and the old one is higher quality and is running hot but can handle the heat so to speak? ......Hmmmm, swapping to a new batt should help eliminate some mystery here or just make more!!...lol.


*Does the rec/reg have its own fuse on one of the red wires?....See below

(BTW, The 20 amp main motor fuse does not have current path BETWEEN the rec/reg's output the battery. The 20 amp main fuse DOES connect here HOWEVER, the current paths for this 20 main fuse are loads AFTER this point. e.g. this main fuse feeds all points down stream of it's connection originating at the starter/battery connection on the starter solenoid and the rec/reg (and charge stator) is the feed for this point in turn.)

 

[georgia088]

Sap to a different batery and test and also check resistance on keyswitch

How do you check the resistance on the key switch?
Thanks!

 

[georgia088]

More $.02.......

Typically not failing in such a way to blow the 20 amp main motor fuse, even the coil shorting to ground or shorted wingings shouldn't blow your 20 amp main fuse, the rec/reg's (a good one) diodes prevent current flow backwards from the directly (*no fuse) connected battery, so no not that I can think of however!! Anything is possible I reckon but i hate guessing, so.....

You can of course test your theory and eliminate the possibility by dis-connecting it and running without it. Just unplug/secure the yellow wires and go crazy WOT! Running w/o the charge coil connected is perfectly safe on the motor/stator.

I'm a bit perplexed on the rec/reg that blew up though.........I'm sorta scratching my head on this one still, and again, that rec/reg could have its input (the charging winding of the stator) shorting to ground, shorting windings and the like and still shouldn't fry like you've reported.........They fry (over time usually) however running too hot, i.e. large loads that pull lots of current.

A s**t battery c/would certainly do this. BUT, why does the old rec/reg still work? Is it getting hot to the touch? Perhaps the new rec/reg that fried was a cheep knock off and the old one is higher quality and is running hot but can handle the heat so to speak? ......Hmmmm, swapping to a new batt should help eliminate some mystery here or just make more!!...lol.


*Does the rec/reg have its own fuse on one of the red wires?....See below

(BTW, The 20 amp main motor fuse does not have current path BETWEEN the rec/reg's output the battery. The 20 amp main fuse DOES connect here HOWEVER, the current paths for this 20 main fuse are loads AFTER this point. e.g. this main fuse feeds all points down stream of it's connection originating at the starter/battery connection on the starter solenoid and the rec/reg (and charge stator) is the feed for this point in turn.)

I am not sure what you mean about the fuse. I have only found one 20 amp fuse and it is located under the cover of the motor. In a housing that clips in next to where the rectifier mounts.
the new rectifier was a cheap one. I didn’t want to spend too much and it not solve the issue. So it is possible that it couldn’t handle the heat as well as the other. Thanks!

 

[Texasmark]

Backing the truck up. I had another look at the wiring diagram and I got my wires crossed....literally....easily done, lots of parallel wires. Sorry for the confusion.

As Sam said, the rectifier regulator output goes directly to the 12v input/distribution ⅜" stud post on the starter solenoid input terminal where the battery red wire connects. The 20 amp fuse is plumbed off this point and supplies loads to the trim control circuits, and the key switch via the 8 pin engine to remote control cable pin 8. The key switch in the ON position sends power to the auxiliary circuits on the purple wire. In the START position it sends 12v via the yellow/red stripe wire to the starter solenoid control circuit via pin 7.

Therefore your battery condition will not be a reason for the fuse to blow....blow out a regulator yes, but not a fuse. That problem has to come from the circuits mentioned above. The confusing part in the fuse blowing is your being at WOT rpms for it to blow.....there isn't anything in that circuit related to WOT rpms to speak of.

 

[sam am I]

I am not sure what you mean about the fuse. I have only found one 20 amp fuse and it is located under the cover of the motor. In a housing that clips in next to where the rectifier mounts.
the new rectifier was a cheap one. I didn’t want to spend too much and it not solve the issue. So it is possible that it couldn’t handle the heat as well as the other. Thanks!

Do you have a picture of the fuse as it sits in the motor? or Click HERE to check as I think this is your motor?. If so, the fuse shown is NOT inline with the rec/reg. That is a main fuse coming off the starter solenoid and is the "main engine fuse"

Merc started adding fuses (20A) on the rec/reg, click HERE to see that picture. Ppl have been adding them over the years to even older engines for safety. This fuse IS inline with the rec/reg output feed. Just making sure of what fuse your talking about.

 

[Texasmark]

Do you have a picture of the fuse as it sits in the motor? or Click HERE to check as I think this is your motor?. If so, the fuse shown is NOT inline with the rec/reg. That is a main fuse coming off the starter solenoid and is the "main engine fuse"

Merc started adding fuses on the rec/reg, click HERE to see that picture. It IS inline with the rec/reg output feed. Just making sure of what fuse your talking about.

I was correcting my mistake as you were posting this.

 

[georgia088]

Do you have a picture of the fuse as it sits in the motor? or Click HERE to check as I think this is your motor?. If so, the fuse shown is NOT inline with the rec/reg. That is a main fuse coming off the starter solenoid and is the "main engine fuse"

Merc started adding fuses on the rec/reg, click HERE to see that picture. It IS inline with the rec/reg output feed. Just making sure of what fuse your talking about.

it is the first picture in your post. The rectifier itself does not have a fuse of its own.

 

[sam am I]

it is the first picture in your post. The rectifier itself does not have a fuse of its own.

Okay got it, ty. I'd disconnect the yellow charge wires that go into the rec/reg, dis-connect the red output wires that come out of the rec/reg and run down the lake WOT. That is if after you install the new battery, leaving everything hooked up proper and it still blows the 20A main fuse.

 

[georgia088]

Backing the truck up. I had another look at the wiring diagram and I got my wires crossed....literally....easily done, lots of parallel wires. Sorry for the confusion.

As Sam said, the rectifier regulator output goes directly to the 12v input/distribution ⅜" stud post on the starter solenoid input terminal where the battery red wire connects. The 20 amp fuse is plumbed off this point and supplies loads to the trim control circuits, and the key switch via the 8 pin engine to remote control cable pin 8. The key switch in the ON position sends power to the auxiliary circuits on the purple wire. In the START position it sends 12v via the yellow/red stripe wire to the starter solenoid control circuit via pin 7.

Therefore your battery condition will not be a reason for the fuse to blow....blow out a regulator yes, but not a fuse. That problem has to come from the circuits mentioned above. The confusing part in the fuse blowing is your being at WOT rpms for it to blow.....there isn't anything in that circuit related to WOT rpms to speak of.

This describes how I believe it to be wired up also..... It is blowing my mind why high rpms is causing the fuse to blow. Could you post a link or pic of the wiring diagram for my motor. The image used to determine my fuse looks exactly like my engine. Thanks again!

 

[georgia088]

Okay got it, ty. I'd disconnect the yellow charge wires that go into the rec/reg, dis-connect the red output wires that come out of the rec/reg and run down the lake WOT. That is if after you install the new battery, leaving everything hooked up proper and it still blows the 20A main fuse.

Ok. Will do..... what will this prove? I really appreciate y’all a help!

 

[sam am I]

Ok. Will do..... what will this prove? I really appreciate y’all a help!

Moot point if its all better with new battery, right? You're going to test with new battery before we get crazy here.......

So, if the fuse still blows with new battery and rec/reg dis-connected, it will show it's not upstream in the charging system (rec/reg and stator charge winding) ...........

If it doesn't blow and you then hook the rec/reg back up (yellows and reds) and it blows again, the output(red wires) of the rec/reg is.........

A) Shorting to or near ground,.

or

B) Not regulating properly and its voltage is exceeding the batteries limit/clamp of around 15/16V thus drawing excessive current (>20 amps). We should have saw this however and we're on the second rec/reg, doubt this is happening BUT, this is additionally how the main fuse could be blown in regards to a flaky rec/reg/charging problem.

My bet is neither A or B and the **new battery fixed it** OR if it still blows with rec/reg dis-connected, its down stream of the fuse somewhere("e").



Not your exact motor but close enough.

** See "B" above EXCEPT in that if you have a shorted battery cell or two, then the batteries terminal voltage clamps and limits at say 11V (not 15/16 like normal) and with the/a GOOD rec/reg who wants and is designed to put out 14.5V at WOT, guess whats going to happen? Yup, excessive current again in the main fuse and perhaps >20A IF the stator and rec/reg(both should be running pretty hot by now) can produce(source) it or near it. The fuse will not vaporize (hard short) per-se however, it will get warm and open like your seeing and TM is asking about. AND, a cheap rec/reg might just blow up in this scenario as well..........

 

[sam am I]

See "A" above is incorrect.........Doh, missed my own gripe I've been preaching for years!! Long day I suppose and a headache to boot, it's this heat, geeeeesh!! Anyway.........The main fuse will NOT blow if the rec/reg's output goes to or near ground, the damn things causes (ooops, "can cause") a freaking fire!!!

Yes Georgia, It's (the rec/reg's output) wired direct to the battery (as per Merc) w/o a fuse for crap sacks, hence the fused rec/regs I linked to above and have recommend or at the least fuses be added for safety. Should be a dern law suit in the mix by golly, dumb move on their part IMO.

 

[georgia088]

Moot point if its all better with new battery, right? You're going to test with new battery before we get crazy here.......

So, if the fuse still blows with new battery and rec/reg dis-connected, it will show it's not upstream in the charging system (rec/reg and stator charge winding) ...........

If it doesn't blow and you then hook the rec/reg back up (yellows and reds) and it blows again, the output(red wires) of the rec/reg is.........

A) Shorting to or near ground,.

or

B) Not regulating properly and its voltage is exceeding the batteries limit/clamp of around 15/16V thus drawing excessive current (>20 amps). We should have saw this however and we're on the second rec/reg, doubt this is happening BUT, this is additionally how the main fuse could be blown in regards to a flaky rec/reg/charging problem.

My bet is neither A or B and the **new battery fixed it** OR if it still blows with rec/reg dis-connected, its down stream of the fuse somewhere("e").



Not your exact motor but close enough.

** See "B" above EXCEPT in that if you have a shorted battery cell or two, then the batteries terminal voltage clamps and limits at say 11V (not 15/16 like normal) and with the/a GOOD rec/reg who wants and is designed to put out 14.5V at WOT, guess whats going to happen? Yup, excessive current again in the main fuse and perhaps >20A IF the stator and rec/reg(both should be running pretty hot by now) can produce(source) it or near it. The fuse will not vaporize (hard short) per-se however, it will get warm and open like your seeing and TM is asking about. AND, a cheap rec/reg might just blow up in this scenario as well..........

ok.... I think I am following you. My peanut of a brain may not can handle all of this though. Let me see if I am understanding. You think bad battery is most likely culprit. If a cell is shorted inside battery it would only handle (let’s say 11v). The charging system is working as it should and putting out 14.5v (there about) because this bad battery can’t handle this excessive current the fuse blows?
If this is the case would the battery still be seemingly functioning properly (cranking, radio, lights etc). Granted I haven’t put a huge strain on the battery while the engine not running, but it still does crank the engine with no issues.
you are also saying if rectifier is shorting to ground it shouldn’t cause fuse to blow, but should blow/catch fire/melt....
thanks!

 

[sam am I]

You think bad battery is most likely culprit.

Leaning heavily that way, yes

If a cell is shorted inside battery it would only handle (let’s say 11v). The charging system is working as it should and putting out 14.5v (there about) because this bad battery can’t handle this excessive current the fuse blows?

Yes, The voltage reg is designed to output 13.8-14.5 and if the battery is locking it to 11V, excessive current in main fuse.

If this is the case would the battery still be seemingly functioning properly (cranking, radio, lights etc).

Yup, it sure can however, your voltage meter on the dash should have reflected a lower then normal voltage when running. Might be intermittent though and pop in and out

Granted I haven’t put a huge strain on the battery while the engine not running, but it still does crank the engine with no issues.

It could, sure

you are also saying if rectifier is shorting to ground it shouldn’t cause fuse to blow, but should blow/catch fire/melt...

I'm here to tell ya, I (as I'm sure many others) know it first hand because i personally was headed into the lake at 43 degrees F one day because just that!! Mine is now fused.

I'll refer you back to the schematic in #17, the battery is directly connected via 1.0 gauge wire to the same stud as the output wires of the rec/reg, SHOULD (what the chances? Hmmm, even small is too much IMO, happen to me) either of those two red rec/reg wires short out internally within the rec/reg to ground (it has internal circuitry that is electrically hardwired to its body AND the body is hard mounted directly to the engine block ) or the block or ANYTHING grounded in route to the rec/reg......PUFF goes those wires!! And also anything in the same loom or surrounding/around/near them. They go white hot in 0.001 seconds!! The main fuse ("f") DOES NOT blow, it's NOT in the current path.

Why those particular two 14 AWG wires were somehow, from the Merc factory mind you, excluded from ABYC standards is beyond me..........Perhaps someone can explain this to me?

Of course this is just my opinion based on observation and experience both professionally and recreationally, it doesn't necessary reflect in whole or part this network or any of its affiliates.

:der: