Logo
FULL SITE MENU

2004 Mercury Four stroke- voltage regulator question

M

Maddawg46

New member
I have an issue with my motor. Was fishing all day everything fine. All of a sudden both my depth finders started flashing and not working. Went to start motor.....dead. Jumped battery from my trolling motor. Started right up. Cruising back to Marina, and there was a steady alarm sound. Shut it down. Went to start again and nothing, dead. Made it back on trolling motor.
Had just enough juice to raise the motor and head home. The 25 A fuse on the motor was blown and melted. I went to replace fuse and as soon as the fuse touched it blew. Disconnected battery and started checking continuity of all red wires that it could get to and other lead to ground.
One of the red wires from the fuse goes to the voltage regulator/regulator. That red wire is dead short to ground. I have no manual or schematic.
I assume my voltage regulator is bad. What do you think?
P.S. I had the regulator replaced with an up garage one due to a recall early last year. Right after that I accidentally hooked the battery backwards. That blew the same fuse? Could that have lessened the life of my regulator?
 
Not familiar with the internal wiring of your regulator, but you have to be careful reversing polarity. On an auto alternator it will fry the 3 return diodes (the ones connected to ground) in a heart beat.

To ensure that the regulator is the problem, disconnect the wiring from it. Measure with your multimeter between the black wire and a red wire. Measure in both directions since some meters have the battery installed reverse to others and until you test your meter against a known good diode where you can read the polarity, you don't know.

At any rate, if shorted in both directions you have a fried diode or two in the regulator. The fact that the fuse blows as fast as it does is attributed to a dead short.

Mark
 
Texasmark said:
Not familiar with the internal wiring of your regulator, but you have to be careful reversing polarity. On an auto alternator it will fry the 3 return diodes (the ones connected to ground) in a heart beat.

To ensure that the regulator is the problem, disconnect the wiring from it. Measure with your multimeter between the black wire and a red wire. Measure in both directions since some meters have the battery installed reverse to others and until you test your meter against a known good diode where you can read the polarity, you don't know.

At any rate, if shorted in both directions you have a fried diode or two in the regulator. The fact that the fuse blows as fast as it does is attributed to a dead short.

Mark
Click to expand...
I'm not real good with electrical stuff. Would having a dead short in the voltage regulator blow that fuse. If I hook up the battery it will blow the fuse. So that must mean there is a short somewhere else.maybe the ignition switch???
 
Maddawg46 said:
I'm not real good with electrical stuff. Would having a dead short in the voltage regulator blow that fuse. If I hook up the battery it will blow the fuse. So that must mean there is a short somewhere else.maybe the ignition switch???
Click to expand...

The symptoms you gave me are perfect for a shorted diode. The jumper reversal in the first place blowing the diodes which then blew the fuse which then provided a path for the batteries to discharge. Simple as 1 2 3 man.

Top of this page says "Boat Engine Parts" for sale. Get you a new rectifier/regulator and go for it' auto parts store for the fuse. And remember red and +, black and -. No swappee!!

Mark
 
Texasmark said:
The symptoms you gave me are perfect for a shorted diode. The jumper reversal in the first place blowing the diodes which then blew the fuse which then provided a path for the batteries to discharge. Simple as 1 2 3 man.

Top of this page says "Boat Engine Parts" for sale. Get you a new rectifier/regulator and go for it' auto parts store for the fuse. And remember red and +, black and -. No swappee!!

Mark
Click to expand...
No, No.....I did that battery hook up a year ago. It's been fine until the other day. I have put 70 hours on the motor since I hooked the battery up backwards. I just thought it might have weakened something in the system.
 
Maddawg46 said:
No, No.....I did that battery hook up a year ago. It's been fine until the other day. I have put 70 hours on the motor since I hooked the battery up backwards. I just thought it might have weakened something in the system.
Click to expand...

70 hrs on something weakened electrically in that kind of circuit is far fetched. So, today, where are you with this problem?

If the fuse blows, remove it. Get a multimeter, and ohm between the down circuit terminal of the fuse holder and the engine block (ground). You have to zero your meter leads first which means just touch them together on your lowest ohm scale. Record the reading....on my meter it's 0.4 ohms.

A 20 amp fast blow (no internal delay) fuse will carry 20 amperes indefinitely. A fuse that has the guts splattered out of it received 5, 10, 20, 100 x it's rating. That's what happens with a dead short with adequate wire size to carry the current.

For 20 amperes to flow in a 12v circuit, 12/20 = 0.6 ohms of circuit resistance. For 5x overload = 0.6/5 = 0.12 ohms. For 10x overload = 0.06 ohms and on and on. So in making your measurement, you add the resistance that is in the circuit to your meter lead resistance. So for a short that would produce a 10x overload and blow your fuse wire to smitherines, and having the 0.4 ohm lead resistance you would measure 0.46 ohms.

Once you have verified your short, it's just a matter of disconnecting components. Pull the rect/regl out of the circuit. Go to the starter solenoid 3/8" stud input terminal where the battery is connected. This is usually a 12v distribution point, and measure the resistance to ground. On your low ohm scale if it measures any resistance it will be 100 ohms or so. If it measures very low then it means that your rec/vr wasn't the problem, something else failed.....course with that kind of current it probably fried the rect/vr any way.

Balls in your court,
Mark
 
I am a little intimidated about the electrical stuff. I think I will take it in, before I fry something. I don't have a schematic. If I did, I would still be Leary about stuff. Thanks for the help, but this is over my head.
 
Maddawg46 said:
I am a little intimidated about the electrical stuff. I think I will take it in, before I fry something. I don't have a schematic. If I did, I would still be Leary about stuff. Thanks for the help, but this is over my head.
Click to expand...

Good idea. Better to be safe than sorry and what it costs you to get it fixed could be a lot cheaper than fixing something that was a casualty in the process of learning.

Mark
 
Back
Top