Fried ground wire

[shadowrider]

Re: Fried ground wire

I have an update. After tightening all ground wires I replaced the fried wire with one of equal length and guage. As soon as I turned on perko switch, pow fried again. Trim pump works if perko switch is on or off, that makes sense because it wired directly to battery. After frying the 2nd wire, I took a voltmeter reading between wire contacts and get 12 volts across them with perko switch in 1,2,& all. Switch off shows no voltage. I am really stumped here. Perko appears to be working fine. Cannot see any chafed wires anywhere. What now ?

 

[Bt Doctur]

Re: Fried ground wire

Just a guess but could you have the positive and negative battery cables reversed? remove all the wires on the batteries neg side except for the negative battery cable.
try removing the main battery cable from the starter and the battery. get another cable or jumper cables and go + battery to starter lug.
nothing should burn or melt.
There`s something missing in your story,just switching on a battery switch should not affect anything.

 

[shadowrider]

Re: Fried ground wire

I know, it is blowing my mind. I checked polarity, again, I have never disconnected the batteries. A few things r not working as I mentioned. The trim guage does not work, was wondering if that shorted, could it be charging the transom, but again it did not work last year and did not fry anything, but I never trimmed drive that high (trailering switch) in the past. I will do more investigating this afternoon.

 

[achris]

Re: Fried ground wire

Use the DMM to determine which is at 12V positive, engine or transom housing. Whichever is the higher will be the one with a problem, like a shorted device, or something like that. Bear in mind that the trim pump and its hoses can carry ground potential, so if the negative has a problem, the current could conceivably go through the hoses, into the drive and try to get back to the battery via the transom housing, and since the only path between transom housing and the engine block is that small bonding strap, that's where it'll go.... Small bonding cable + high current = smoke!

Just an idea.....

Chris.........
EDIT: Just had another thought. Being an ali boat, if the main negative from the battery to the engine block is not good (as in bad contact) then current will go through the hull, then the transom assembly to get back to the engine... Same result....

 

[wellcraft-classic210]

Re: Fried ground wire

At this point is going to be process of elimination-- disconnect possible compenents that could be shorting and try agan. Motors, solenoids, anythig that may get water inside, and wiring are all possible causes. Its got to be somethng with fairly high power or improperly fused as its not blowing any fuses. You may want to look into that as part of the repair as the wrong fuse in a socket can be a fire hazard.

You may also be able to use the ohm meter function on the dvm to see if anything on the positive side has a path to ground. Make sure the battery power is not present on these tests or you will get false readings & could damage the meter.

 

[FreeBeeTony]

Re: Fried ground wire

Without the ground wire connected I would do the following:

Turn the Perko switch on.
Using a DVM check the voltage drop between the negative battery terminal and the engine block.......it should be 0.0 volts.
If the voltage drop is higher than 0.1-0.2V that would indicate a poor connection between the negative battery terminal and the engine block.

 

[shadowrider]

Re: Fried ground wire

I may have found something. I traced the positive battery down to the starter, I was able to wiggle it. Further inspection revealed a corroded loose relay or whatever this thing is I have included a pic of. I am heading down to parts house to see if I can get a new one. Can you tell me what this is called ? Thanks

 

[stonyloam]

Re: Fried ground wire

Fuse http://www.mercruiserparts.com/showSpecialPicture.asp?pn=79023A91 #12 here http://www.mercruiserparts.com/Show...63&bnbr=10&bdesc=STARTER+MOTOR+AND+ALTERNATOR

 

[FreeBeeTony]

Re: Fried ground wire

Don't think that's your problem.......you should pick up a cheap DVM while you're out.

 

[Blacksting]

Re: Fried ground wire

i'm having a problem w/ my slave selonoid and glad i have a slave . why would they put a fuse there ? you can barely get to my starter , let alone change a fuse in that location . worse than that , can anyone else see the irony here ? ,.........." fused selonoid does'nt protect nuttin "

 

[wellcraft-classic210]

Re: Fried ground wire

If that is not it keep looking a Short ciruit. Something is most likely making a direct connection from the + 12v side to the transom area where the wire fried ( or something that's connected to it ) and thats rasing the voltage.

Process of elimination.

 

[achris]

Re: Fried ground wire

i'm having a problem w/ my slave selonoid and glad i have a slave . why would they put a fuse there ? you can barely get to my starter , let alone change a fuse in that location . worse than that , can anyone else see the irony here ? ,.........." fused selonoid does'nt protect nuttin "

The solenoid is not fused... Have a look at your circus diagram... The fuse is protecting the alternator and the rest of the engine from nasties generated by crappy wiring standards elsewhere on the boat!

 

[stonyloam]

Re: Fried ground wire

You could try disconnecting the burnt wire and with the voltmeter measure from the hull to the battery neg, first with the switch off, then turn the switch back on. I'll bet you have +12V on the hull (maybe).

 

[Blacksting]

Re: Fried ground wire

The solenoid is not fused... Have a look at your circus diagram... The fuse is protecting the alternator and the rest of the engine from nasties generated by crappy wiring standards elsewhere on the boat!

.......well i was refering to the location above everything else . but it looks to me that the fuse is connected directly to the sel. . and what circus drawing are you refering to ?

 

[achris]

Re: Fried ground wire

.......well i was refering to the location above everything else . but it looks to me that the fuse is connected directly to the sel. . and what circus drawing are you refering to ?

The physical position of the fuse is on the solenoid, yes, but it's position in the circuit is where I said... They mount it on solenoid because there's not a really convenient other place for it...

Chris...........

Circus diagram in the manual.... :facepalm:

 

[shadowrider]

Re: Fried ground wire

I disassembled and cleaned the 90 amp fuse, checked for continuity and visually verified it was intact, then put back on starter, tightened up everthing, turned on perko and still have 12 volts across ground circuit. I have obtained a dmm. I have found that the transom is positive motor is negative. I eliminated the trim pump and the stereo ( 80 amp circuit ), as possible sources. In fact I disconnected everthing except positive and negative battery terminals. I am going to remove the perko and look inside it. It is mounted to an aluminum panel on an all aluminum boat, will check to see if it has water in it, or grounding itself maybe?

 

[achris]

Re: Fried ground wire

.... I am going to remove the perko and look inside it. It is mounted to an aluminum panel on an all aluminum boat, will check to see if it has water in it, or grounding itself maybe?

Ah.... I ALWAYS mount battery switches with a sheet of plastic card across the back... Stops that problem.... Didn't even think about that :facepalm:and it makes sense. Hull's at 12v, engine's at 0v... Lots of electrons will make their way to the engine through the only path.... the bonding wire...

Good find...

 

[wellcraft-classic210]

Re: Fried ground wire

Looks like your on the right path

short circuit

a faulty or accidental connection between two points of different potential in an electric circuit, bypassing the load and establishing a path of low resistance through which an excessive current can flow. It can cause damage to the components if the circuit is not protected by a fuse

 

[stonyloam]

Re: Fried ground wire

It is mounted to an aluminum panel on an all aluminum boat, will check to see if it has water in it, or grounding itself maybe?

That sounds like it could be the source of the problem, somehow your switch is shorted to the hull.

 

[shadowrider]

Re: Fried ground wire

Problem resolved!!!! I removed the perko and found the center contact had chafed through the paint and was in direct contact with raw aluminum. I ground 1/8" off all 3 contact studs and covered them with a plastic jar lid. Transom is no longer positive, I will replace the fried ground wire later today. Thanks for all the help and support guys, Shadow