72 johnson hydro electric smoking from throttle/ignition housing

[starkizzle]

I have a 72 Johnson Hydro Electric drive 125 hp outboard I have been working on for some time. I just recently got a lot of help from you guys for the shift solenoid. After finally having the thing on the water for more than 20 minutes I noticed smoke coming from inside the throttle controls at the dash. Not heavy, but gradually getting worse. I first started looking for it because I smelt what reminded me of heating solder.. maybe more like welding.. Then i noticed the smoke starting to come out.. So I just took it apart and the Diode looks like it is possibly popped? or something melted to it, it is hard to tell.. but there is also small metal balls (like you would get from solder) in the melted stuff around the diode.. I am going to try to get a picture of the hole thing on here in a second, I was just wondering if anyone has had any experience with something liek this? and what what might be some causes and solutions?

 

[jimmbo]

Short to ground in the wiring. Chafed wire, pinched wire. Mis wired
Wiring diagram for your engine

http://maxrules.com/graphics/omc/wir...25_1971-72.jpg

 

[starkizzle]

Thank you Jimmbo, that was what I looked for first. I tried -unsuccessfully to upload some pictures, but the diode had a split in it and near it was black plastic with bits of melted metal in and around it.. I cut the diode out and from my understanding, they are only suppose to let power through one way, this one had 0 resistance from either direction. I noticed that the wire looked alittle corroded on the inside, is this to be expected with a boat this old? This diode goes from the ignition switch to the shift switch in the control housing.. Anyway around it? I am concerned that replacing it will just lead to to the next symptom of a much bigger wiring problem... This is not the first case of hot wires in this boat, its basically all I have been dealing with for the last month.. The green shift wire that comes out of the shifter switch in the control and goes to the lower unit was heating up until I replaced the shift solenoid in the LU.. Is the bad wires just causing everything to short/blow??

 

[jimmbo]

The wires are reacting to excessive current. Usually a short is responsible. The diode in the control box is called a 'blocking diode'. it is to prevent the engine from continuing to run when the key is turned off(one would think the key would do that), and to ensure the gearcase shifts to neutral when it starts.
There are two more diodes in the shift circuit. They feed directly off the stator( in the diagram it shown as diode near the juction block)(physical location should be in the wiring harness near the terminal block towards the port cylinder head, wrapped in tape) If one of these went bad it may play havoc with the wires to the shift solenoids and/or the diode in the control box. My book says its failure will cause the unit to shift into forward immediately after engine is turned off(that makes no sense, as the engine needs to be running for it to shift out of forward).

 

[starkizzle]

Well that would be why turning the key off does nothing right now I guess? Am I going to continue to have electrical problems the why the wires are? Is replacing this diode a fix or is it bigger?

 

[starkizzle]

Also, I had recently replaced the old 20amp glass fuse when I fixxed the neutral safety switch, with a blade type. It is also a 30 amp fuse thou.. This was what was able to point me towards the shift solenoid, because the wire was getting so warm, May the bigger fuse be allowing for problems? because it's not blowing?

 

[starkizzle]

I just ordered a new diode, should I be looking for anything else? I will check out the other diode JImmbo, although I only see the two in that diagram. The one in the control box and the one that is in about the middle of the screen.

 

[jimmbo]

The one in the middle of the wiring diagram will be a double diode, like half of a bridge rectifier. The cathodes are connected and one of the anodes is connected to one of the stator wires, and the other to the remaining wire. The cathode is connected, via a long wire to the cathode of the diode in the control box and to shift switches.

 

[starkizzle]

am I able to test that one?

 

[jimmbo]

yes. I'm sending you a pm

 

[starkizzle]

OK, I gave that all a shot, I sent you a couple messages back

 

[jimmbo]

I would assume the shifting diodes to be bad according to your test results. Diodes can fail and not stink, excessive current does the baking. I would also check the main rectifier, if it fails it will play havoc to the rest of the system. I'll PM you the test procedures, but i'll have to switch computers, scanners not hooked up to this one

 

[starkizzle]

Thanks again for the help, I will look at the rectifier this afternoon.

 

[starkizzle]

Looks like the shift diode is good, just had to play with my meter, I had consistent results, the rectifier was only showing good reading from the wires to ground, but nothing between yellow and red wire or red and yellow/grey, we shall see how the aftermarket parts fair soon enough. Thank you again.