Finding a short in wiring?

[Saskatoon2005]

My battery gets drained on my 1975 Johnson 70 HP 3cylinder outboard. I have power tilt and trim, and electric start, and a stereo.

How do I isolate the short in my wiring...I have heard it is quite difficult to locate, but am asking for tips on finding the problem. I do not want to pay someone else to do it for me.

I have a Fluke brand electrical tester, and would like to know how to use it to find the short.

Thanks,

Patrick

 

[Silvertip]

Re: Finding a short in wiring?

You do not have a short. If there was one a fuse would blow. If the circuit was not protected by a fuse you would have smoke and fire. The next thing to check is to make sure you have a battery that is capable of holding a charge. Just because you stick a charger on it does not mean its a good battery. Have it load tested at any auto store (NAPA, Auto Zone, etc). Since you have a radio and I will assume it has a clock and station memory, that stays active even though the radio is turned off. If it didn't you would continually need to reset the clock and none of the stations would stay set. However, if this was the problem, the boat would have to sit for a couple weeks to kill the battery as the drain is not that much. What is more likely is that the rectifier is bad (as in a bad diode) that allows the reverse current flow. Disconnect the rectifier and see if the battery stays up. If the meter has a resistance (ohms) function, set the meter to ohms, disconnect the rectifier and place the red lead on one of the input leads, and the black lead on the output. Note the reading. Now reverse the meter leads and test again. A good diode will measure higher resistance in one direction than the other. If the diode measures the same in both directions, its bad. Repeat the test on the other input lead.

 

[Saskatoon2005]

Re: Finding a short in wiring?

Yes, I did find that the rectifier was bad. I changed the rectifier, but it did not solve my draining issues. I am planning to put my radio (memory wire unhooked) to its own battery (deep cycle) and see how that works. I do not want to run the risk of having my battery short out my rectifier and leave me stranded. I would cruise around for a couple of hours on the lake, and then turn the motor off, but when I went to restart it, I would have to use a booster pak, as the battery was too low to turn the outboard over.

I have had my battery load tested at canadian tire, and they told me it was fine. So it is not the battery. It is not the rectifier, and I have not used the radio as of yet, thinking it could be that as well.

 

[Moody Blue]

Re: Finding a short in wiring?

Something does not sound right. A good battery, would not run down that quick unless there is SIGNIFICANT drain. For example, you can leave you car headlights on for several hours with the engine off and still be able to start the car.

Have you verified that your motor is actually charging the battery? Measure the voltage at the battery with the motor running. You should measure about 13.7 volts.

Have you considered installing a master disconnect switch? A new pos cable from battery connects to disconnect, then the original battery pos cable connects to the other side of the disconnect. When you turn the disconnect OFF, ALL loads are disconnected from the battery. Acts as a good theft deterrent as well .

 

[Silvertip]

Re: Finding a short in wiring?

Get the word "short" out of the picture. Your battery will not "short" the rectifier. A shorted rectifier will however drain the battery. Whatever is connected to the battery likewise will not short the rectifier. Rectifiers short (or open) because they are electronic devices and they can fail for no apparent reason. If you are positive the rectifier is ok and the battery is ok and it still dies that quickly, there are some pretty serious current drains going on and the only thing on a boat that would draw that much power to kill the battery is the rectifier.

 

[Saskatoon2005]

Re: Finding a short in wiring?

I am curious to know if after testing the running motor and it is 13.7 volts dc as it runs, how can you check that something is draining the battery after you have stopped the motor....what connections do you check?

I am suspect of the trim/tilt unit draining, or something on the motor. I have a stereo but it will soon be wired to its own deep cycle battery mounted in the bow.

 

[Saskatoon2005]

Re: Finding a short in wiring?

Where can I find a wiring diagram for the power tilt trim unit. Its funny cause i bought a manual for the outboard, the manufacturers manual, but there is nothing in it about the power tilt trim unit. I know it must run on a solenoid because there is an extra one in the bilge area of the boat. I haven't followed all the wiring because there is a nest of wires and I am kinda scared...LOL!

I am hoping that someone has a digram of how the wiring ties into my outboard wiring...for anyone out there that can help, my outboard is:

1975 Johnson 70 Hp Outboard. It is a 3 cylinder outboard. I just love this motor, but need help getting it running perfect.

Thanks All

Patrick

 

[eurolarva]

Re: Finding a short in wiring?

Try disconnecting the battery and hook the ohm meter to the battery leads that go to the motor. Start disconnecting things like depth finders, radios, lights until you reach the highest ohms on the meter. Which ever component you disconnect with the highest jump in ohms is the culprit. Main way to fry a rectifier is to accidently hook the cables up backwards even for a second.

 

[Silvertip]

Re: Finding a short in wiring?

A good way to fry your meter is to set to any resistance scale (ohms or "R") and touch it to a live circuit. When measuring resistance the meter uses it's own internal battery. So unless you understand what you are doing, resistance testing may not be the best way to do this. The possibility of a tilt & trim solenoid sticking is certainly possible and the way to test that is to disconnect the power to it. But since you have a drain that kills the battery quickly, I cannot believe you haven't seen smoke, burned some wiring, or blown some fuses. My suggestion is to disconnect all the wires from the positive terminal on the battery. You should have at least two. One large battery cable goes to the starter solenoid. The other one is the +12 volt feed for the boat related items. As dusk approaches, touch the smaller wire to the POS post and see if it makes a significant spark. If none, then do the same with the large battery cable. If none, you very likely have a bad battery. Sorry if you said you had it tested but a significant draw will make a spark. If you do get a spark on the large cable, the draw is on the engine side. If the spark is on the small wire, the problem is on the boat side. Determine which system is involved and we can go from there.

 

[Saskatoon2005]

Re: Finding a short in wiring?

I will definately try these and then get back to you guys. Thanks for the ideas.

Patrick

 

[eurolarva]

Re: Finding a short in wiring?

Try disconnecting the battery and hook the ohm meter to the battery leads that go to the motor.

Maybe this was not worded very well. by battery leads I mean the cables not the battery. If battery is disconnected the battery leads should not have any voltage unless there is a capacitor in there holding a charge. Would not hurt to put the meter on DC Volts and verify there is not voltage on the battery cables.

 

[Moody Blue]

Re: Finding a short in wiring?

Here is how you can measure current draw from the battery IF you have a meter capable of measuring 10Amps DC. You most likely will need to change the (+) meter lead position to the location that says 10A.

Turn OFF all accy's (lights, pumps, radios, everything.) DO NOT ATTEMPT TO START THE MOTOR.

1)Remove the NEG cable(s) from the battery.
2)Connect the (+) meter lead to the NEG battery terminal.
3)Connect the (-) meter lead to the disconnected battery cable(s).

If there is any current draw it will be measured on the meter. Most meters will only be capable of measuring 10Amps max for a brief time. If the draw is more than 10Amps the internal fuse in the meter will blow.

Good luck.

 

[Saskatoon2005]

Re: Finding a short in wiring?

Yes,

I have a Fluke 73 multimeter which in fact DOES have a 10A (fused) plug connection. Do I put the black (negative) probe in the fused plug 10A fused connection?

 

[Moody Blue]

Re: Finding a short in wiring?

Red (+) lead into the 10A socket. Black (-) lead stays in Com socket.

 

[Saskatoon2005]

Re: Finding a short in wiring?

Thanks, I will test that out and let you know what happens...just so I am clear...

if the fuse blows then that means that the motor is drawing more than ten amps and there is a short somewhere?

Thanks,

Patrick

 

[Silvertip]

Re: Finding a short in wiring?

Gee -- you really have this short thing on your mind. No! If a circuit has a 10 amp fuse in it and you are trying to draw more than 10 amps through it the fuse will blow. That's why its there. Yes, IF the circuit has a short it will also blow the fuse. But just because the fuse blows does not mean you have a short. A stalled electric motor draws lots of current. It doesn't mean it is shorted. Tight bearings will do that.

 

[Provo5]

Re: Finding a short in wiring?

In stead of using a meter between the battry and circuits put a test light in its place. The test light will come on if there is a complete circuit. Start disconnecting circuits until the test light goes off to find your draw. Years ago I had a ignition switch that was not turning completely off that drained my battery.