Troubleshooting a Short

[FishHunt23]

I have a real PITA problem with my 1988 Evinrude 70. There is a short that is causing the fuse in the engine (20A, located in a red boot near where the wire harness from the control box plugs in under the hood) to short on an intermittent basis.

Sometimes it happens when I turn the key. Sometimes it happens when I hit the trim switch. But sometimes it happens even when the ignition key is off, and it'll blow the fuse the second I replace it. Then everything will be 100% fine for months at a time. It's crazy.

I replaced the control wire harness (red plug). I disconnected the dash gauges. I've re-wired everything else (this was a project boat, so I did that anyway). The contol box has been replaced and the problem persists, so it isn't in there.

I figure I've got a worn/bare wire somewhere that is bumping into something. Or a bad ground, though if that were the case I think it would be more consistent.

Does anyone have any advice on where to look for the problem? Locating a short can be a real bear of a project in my experience. Thank you.

 

[ezeke]

Re: Troubleshooting a Short

Your 20 amp fuse is in line to the ignition switch through the main harness wiring, so the wiring and the ignition switch would be the first place to look.

The wiring in the harness is too small for accessories, so make sure that the positive post off the ignition is just used to activate solenoids at the engine and to provide power for gauges and maybe a <4 amp horn.

Any other accessories should be wired off of a separate line from the battery.

 

[splitshot]

Re: Troubleshooting a Short

well put

 

[FishHunt23]

Re: Troubleshooting a Short

I did a little work on the boat tonight. With the wiring harness to the remote disconnected at the engine, the short persists. I'm following the shop manual as best I can and have two questions:

1) The block that the rectifier connects to should have a red/purple wire coming into it according to the diagram. There isn't one. The red/purple from the fuse goes to the front of the engine to the plastic box. Whats that plastic box called? And why would I be a wire short on the wire block at the rectifier?

2) The rectifier/diode appears to be bad. The stator shows the proper ohms on that test, but may be grounded according to the second test which will require a repair or replacement. My starting battery has never charged, so I fully expect that there is a problem with one or both these components. Could the stator be causing my short? I'd guess yes, in which case I'm going to have to get at it. Any advice for getting the flywheel off without a puller? Looks like I have to go tool shopping, which is normally a fun task but I'm not eager to spend the $$ right now if I don't have to.

Thank you all for your help.

 

[FishHunt23]

Re: Troubleshooting a Short

Thinking out loud: the short has not been consistent, but the battery has never charged. Perhaps the rectifier is bad, and the stator is periodically grounding out ... meaning I could repair it somehow. How does a stator usually ground out? The wires appear OK.

As long as I'm at it, what is the gray/brown/black wire connecter that hangs off the back of the engine? There's nothing connected to it, and it doesn't appear on the wiring diagram that anything should be connected to it. Just curious. Thanks.

 

[ezeke]

Re: Troubleshooting a Short

Running with a bad rectifier can put your whole ignition system at risk, so disconnect it until you can have it tested or replaced; the engine can run fine without it.

If you had a VRO, the black, grey and tan wired amphenol plug should be connected to it for the low oil warning.

 

[FishHunt23]

Re: Troubleshooting a Short

I had a VRO, so that makes sense. The pump has since been replaced with a straight fuel pump and I'm running mixed gas. Thanks.

Any more advice on where to look for the short? I'd hate to tear the engine apart any more than I have to.

Thanks very much for your help. This is a great forum.

John

 

[b717doc]

Re: Troubleshooting a Short

Take a paper clip, or something metallic, jump the fuse holder, and wherever you see smoke / fire, that's you culprit...(Just kidding, please don't do that).

 

[luv2b0at]

Re: Troubleshooting a Short

I learned in my Crypto maintenance years, if you let the smoke out, the parts don't work.

 

[luv2b0at]

Re: Troubleshooting a Short

I was having a problem with the 20 amp fuse on my 1999 10 HP 4 stroke. It turned out to be a problem with the starter itself. The engine had been dropped in ocean water (by previous owner) and wasn't cleaned off well enough. The starter corroded up. I could start and run it by pull starting with a rope. As soon as the starter was cleaned up and rebuilt, it worked fine. Could it be an intermittant problem with the starter on your issue? Just a thought.

 

[Silvertip]

Re: Troubleshooting a Short

The input or hot side of the fuse comes from the starter solenoid so nothing ahead of that point would create the problem. The output or load side of the fuse splits into two red-purple wires. One goes to the terminal strip on the engine and the other goes to the large red remote control plug. If the problem occurs with that large connector disconnected, then the problem lies between the engine side of the plug and the fuse. If your engine has tilt & trim, that circuit can cause the problem. Remove the tilt and trim relays and see if the problem occurs. If not, you found the circuit but it will take further diagnosis to identify what is wrong in that circuit. A stuck relay or perhaps some chaffed wires around the tilt/trim motor or a bad trim motor are all suspect.

If it occurs only when the plug is connected, then the issue is in the harness wiring between the engine and some point forward of that.

 

[FishHunt23]

Re: Troubleshooting a Short

Silvertip, thanks for the insight. The short continues to occure with the control plug disconnected. I'll check out the T&T as soon as I can.

 

[Randybeall]

Re: Troubleshooting a Short

Disconnect the rectifier, if you have an ohm meter you can test it. It is not unusual for a diode to short and cause what you have. You can even run the engine with the rectifier disconnected, you will just have no charging system. To test the rectifier, attach one lead of the ohm meter to the ground of the rectifier case. With the leads disconnected test each one with your other ohm meter lead. They all three should be the same, very low resistance or very high resistance. Swap your ohm meter leads and test again. All three leads should be the same, low resistance if they were high before, high resistance if they were low before. Any deviation is a bad rectifier and likely your short. According to the manual I have the resistances should be zero and infinity, however I have seen some which had as much as .5 ohm resistance on the low side.

 

[ezeke]

Re: Troubleshooting a Short

This is apparently a 1988 motor with power tilt and trim so it probably has a water cooled regulated rectifier which cannot be tested reliably with an ohmmeter. Your best bet is to disconnect it until you have the rest of the problems worked out.

I agree with Silvertip, the PT&T circuit is probably overloading the fuse.

You could add a separate fuse for the PT&T so that the relays are on their own circuit.

 

[FishHunt23]

Re: Troubleshooting a Short

You guys are impressive. The short is in the T&T relays. When I disconnected the hot wire that comess into the relay box the short disappeared. I reconnected it and got no short, but as soon as I hit the trim switch the short reappeared.

Here's what's interesting... The inside of the box is clean, but when I disconnected the relays themselved from the harnesses the contacts are covered in a brown, sticky goo ... varnished somehow. The engine got wet years ago, so I assume it's one of the last problems resulting from that (because I've fixed everything else). But I would have expected rust and corrosion. Instead I found brown goo.

WD-40 cleaned up the contacts on the relays nicely, and I verified that they work with an ohmmeter. All good. The difficulty I found is in cleaning the relay harnesses. I sprayed them with WD-40 and wiped them down, but the goo is in the contacts inside the harness. I used the relays to get some of it out by repeatedly pulling them out of the harness, but we'll see how well I can clean them. I may need to replace.

The rectifier is bad, but I think the stator is as well. I don't think either component has/had anything to do with the short. I will continue to investigate those components in order to get a charge back to the battery. I haven't had that luxury since I bought the boat!

Thanks a million for all the help.

John