Finding a short

[DCS30]

Hey guys, I'm not sure if this should be posted here or in hull repair, so I'm sorry if it's the wrong section.

We have a 1978 Starcraft i/o, and the rivets below the waterline are dissolving like crazy. Every year we have to try to patch them up, and it's at the point that I don't feel safe in it anymore. It looks like electrolysis. I cleaned the hell out of the plate on the drive, and it barely did anything. So I'm thinking there must be a short somewhere. How does one locate a short in a boat?? Thanks in advance.

 

[Scott Danforth]

is there any wire anywhere screwed to the hull?

did someone try to use the hull as a ground?

did you use treated lumber on the trailer or in the boat?

 

[dingbat]

Check for continuity between the negative post on the battery and the hull.

If you have continuity check for voltage between the hull and the negative post on the battery.

 

[Bondo]

Ayuh,..... Havin' gone through that before, My Guess is that something on yer boat is wired such that the hull is used as a ground, for a light or other electrical appliance,......

Everything electrical, should be wired with power, 'n a dedicated ground wire back to a buss, then to the battery's ground(-) post,.....

The Only ground connection to the boat, should be the ground strap from the battery, to the motor's block,.....

I my case, 2 cockpit lights were grounded to the hull to work,....
Disconnected those lights, 'n the massive corrosion, Stopped,....

 

[DCS30]

is there any wire anywhere screwed to the hull?

did someone try to use the hull as a ground?

did you use treated lumber on the trailer or in the boat?

everything, other than a stereo added about 30 years ago, is still original from the day my dad bought it in 1978. this rivet issue only started a handful of years ago

 

[DCS30]

Check for continuity between the negative post on the battery and the hull.

If you have continuity check for voltage between the hull and the negative post on the battery.

continuity?

and how does one check the voltage between the hull and negative post?

 

[DCS30]

Ayuh,..... Havin' gone through that before, My Guess is that something on yer boat is wired such that the hull is used as a ground, for a light or other electrical appliance,......

Everything electrical, should be wired with power, 'n a dedicated ground wire back to a buss, then to the battery's ground(-) post,.....

The Only ground connection to the boat, should be the ground strap from the battery, to the motor's block,.....

I my case, 2 cockpit lights were grounded to the hull to work,....
Disconnected those lights, 'n the massive corrosion, Stopped,....

i'll look into that this spring. the only ground i can think of is on the drive itself, but it's connected to itself, if that makes sense.

 

[Bondo]

i'll look into that this spring. the only ground i can think of is on the drive itself, but it's connected to itself, if that makes sense.

Ayuh,..... The drive, transom, 'n motor will have bonding straps, which is just fine,......
The Only ground to the boat should be the battery's (-) negative to the motor's block,.....

 

[Scott Danforth]

everything, other than a stereo added about 30 years ago, is still original from the day my dad bought it in 1978. this rivet issue only started a handful of years ago

something had to change in the "handful of years"

 

[dingbat]

continuity?

and how does one check the voltage between the hull and negative post?

“Continuity” = connected

Check Continuity:
Set meter to read “continuity”
Touch one probe to hull
Touch other proble to battery negative terminal
You should get no reading between the two

Check voltage:
Meter set to read dc voltage.
Positive probe on hull
Negative probe on battery negative post

Make sure you have everything turned ON that you would normally use during an outing. Sounder, bilge pump, etc.

Meter should read 0 volts.

If you get a reading, start turning things off one at a time in an effort to isolate the problem to a single circuit or components.

 

[DCS30]

“Continuity” = connected

Check Continuity:
Set meter to read “continuity”
Touch one probe to hull
Touch other proble to battery negative terminal
You should get no reading between the two

Check voltage:
Meter set to read dc voltage.
Positive probe on hull
Negative probe on battery negative post

Make sure you have everything turned ON that you would normally use during an outing. Sounder, bilge pump, etc.

Meter should read 0 volts.

If you get a reading, start turning things off one at a time in an effort to isolate the problem to a single circuit or components.

thanks! i'll be sure to check this out next month once it's out of storage. stupid question, but every multimeter has a continuity setting?

 

[DCS30]

something had to change in the "handful of years"

no, it's completely original. new battery, at one point an electric fuel pump for a couple years, then back to mechanical, but the problems started before that was installed, if i recall correctly. nothing else has been changed outside of regular replacement of burned out components.

 

[dingbat]

thanks! i'll be sure to check this out next month once it's out of storage. stupid question, but every multimeter has a continuity setting?

Never met one that didn't