1980 80hp mercury tilt and trim blows main fuse going down

[rookie456]

I have a new to me 1980 mercury 80hp ser# 5773499. The tilt and trim was not hooked up when I bought the motor. When I hooked up the tilt and trim, i found out that the motor didnt work, cause it was all rusted inside. I removed the motor and the top of the reservoir and replaced it with a brand new motor and reservoir. The motor works fine going up, but blows the main 20amp fuse when i move the motor down. If I disconnect the blue, green, and black wires that go into the trim motor from the solenoid, I can press the down button on the controls and the main fuse does not blow.
With all of that said, can I assume that the tilt motor is blowing the fuse?
I am thinking that is what is happening, since the fuse doesnt blow when the motor wires are disconnected.
I am attaching a wire diagram of my tilt trim set up, and also a wire diagram of my control box for reference.

Thanks

 

[rookie456]

I really dont want to send this motor back if it is working. I decided to see what kind of readings i would get with a multimeter. when pressing the down button, I am reading 12 volts on the green wire. when pressing the up button, 12 volts on the blue wire. since I assumed the motor was bad, I took the motor and reservoir off of the pump earlier. Since I was reading 12 volts and not blowing a fuse, I decided to hook the motor up. I was able to run the motor with the up button and the down button without blowing a fuse. Now I am wondering if it was because the motor wasnt under the load of pumping the fluid. I think I am going to have to seal up the reservoir and try the motor under a load. Does anyone know an easier way of draining the reservoir then removing the fill screw and draining it from there?

 

[Texasmark]

You may be onto something with the no load vs load comment. Green grass, blue sky: Green is down. What is that component in your Fig 1 in the green line?

Have you attempted to run the unit under load since you ran it successfully unloaded? If so, what happened.

Couple of outside thoughts here. You could have some binding that occurred as a result of the rust associated with the old motor or in your engines swivel pin that had to be over come. I don't have my manual any more but there is a switch on the side of the reservoir that allows for fluid bypassing when you want to manually raise or lower your engine. Might switch to bypass and see if the engine raises and lowers by hand without binding. You could have had fluid in the wrong place initially which caused a pressure spike which caused to motor to work against high pressure fluid which would cause more current to flow and could have blown the fuse.

Can't think of anything else. If the motor had an internal short, it would appear under low as well as high current so I wouldn't suspect that. Might put the switch in the bypass position and just run the motor up and down with everything functioning except no pressure and the engine doesn't move. Then rotate the switch to the normal position and run it again. If it doesn't blow the fuse, run it up and down a few times to get everything limbered up.

Mark

 

[rookie456]

What is that component in your Fig 1 in the green line?

Thanks for the reply.

The component in figure 1 is a screw terminal that allows you to connect the green wire from the motor to the green wire from the harness.
As far as a bypass, I am not sure. There is a valve for reverse lock. If I turn the valve clockwise, I am able to lift the motor by hand, counterclockwise locks the motor from being lifted by hand. When I operate the motor the engine goes up and down wether the valve is clockwise or counterclockwise.
I didn't have the time yet to put it all back together, so the hoses a are not hooked up which allows me to move the engine by hand, it seems to move freely, so I don't think it is binding.
I have read through my manual a couple times, I haven't seen anything about a bypass. I think there would have to be one, in case the motor gets stuck in the up position.

 

[Texasmark]

Well you answered the question. I knew a relief screw was on the unit. Never used it, just assumed it's function. Hear you on the "terminal block". Ok with that.

Now that you know you have no binding, and nothing shorting out, if you continue to blow fuses under load then you may in fact have a shorted motor.

However, I'm a mechanism guy...."stuff" doesn't happen!!!!! It's caused and cause is a mechanism which is your smoking gun. Thinking about what could be wrong with a motor that will run properly unloaded vs loaded, there are two main elements:

1. Binding bearing. Under load a bad bearing, one having been inadequately lubed at the factory possibly, might bind and blow the fuse. If you blow it again, you might take a metal pipe and put it on the motor housing while raising and lowering the cylinder unloaded. See if you hear noises in the down position you don't hear in the up.

2. Electrical. That could be heat causing wires to move where they might touch another wire with inadequate or no insulation (varnish) causing a short. Brushes could be binding. Armature electrical connections, where the brushes ride, could be arcing due to some type of contamination from the factory. Bad solder/crimp joint/terminal lug/locking screw that would allow low currents to pass when unloaded, but would get hot and malfunction under high current. However most problems of that sort are the opposite. Too much resistance in the circuit so inadequate current passes to run the motor.

Good luck,
Mark

 

[Chris1956]

I do not think that PTT unit was intended to be fused. Of course, unless the motor is in reverse, it would be hard for me to see why running the PTT down would use more than 20A. Perhaps you have some low voltage, causing the motor to pull more amps? I would check the condition of the wiring and connections, especially the battery to PTT motor connection and also make sure the ground wire is good and clean.

 

[rookie456]

The PTT isn't fused separately. The fuse that is blowing is the 20amp main fuse on the red wire going to the starter solenoid. The best I can tell is that the PTT is hooked directly to the battery, and it draws power thru that direct connection when you move the motor up. When the motor is moved down, it draws power thru the power line that has the main 20amp fuse on it. I'm gonna clean up all my connections and try again and post my results.

 

[Fed]

The PTT should be stand alone & not connected to the motor wiring at all.
It needs to be connected straight to the battery positive & negative.

 

[Texasmark]

The PTT should be stand alone & not connected to the motor wiring at all.
It needs to be connected straight to the battery positive & negative.

I gave my manual away with my boat but as I recall the PTT on my 2002 90 was behind the 20 A fuse with all the other power wiring. Reason is burning up your wiring harness if you have a short circuit.

 

[rookie456]

I have the quicksilver commander control box that has the trim buttons and the trailer button on the stick. The control box has the main cable coming out of it that connects to the power head wiring harness. The control box also has a four wire bundle that turns into a three prong connector that connects to the tilt trim motor. When I press the up button on the stick, I read 12 volts on the red wire in the 3 prong harness, when I press the down button, I read 12 volts on the green wire of the 3 prong harness. All that being said, if I hook up my trim and tilt motor directly to the battery, and I don't hook up the main wire harness to the battery, my trim tilt does not work. So, my PTT is not a stand alone unit.

I took the PTT motor off of the pump. It seems the copper wires attached to the brushes were rubbing on the armature, that shredded a lot of the copper. I'm guessing the armature was not installed properly and was causing the fuse to blow. Im sending back the motor for a replacement, I hope the company I got it from covers it.

 

[Texasmark]

I have the quicksilver commander control box that has the trim buttons and the trailer button on the stick. The control box has the main cable coming out of it that connects to the power head wiring harness. The control box also has a four wire bundle that turns into a three prong connector that connects to the tilt trim motor. When I press the up button on the stick, I read 12 volts on the red wire in the 3 prong harness, when I press the down button, I read 12 volts on the green wire of the 3 prong harness. All that being said, if I hook up my trim and tilt motor directly to the battery, and I don't hook up the main wire harness to the battery, my trim tilt does not work. So, my PTT is not a stand alone unit.

I took the PTT motor off of the pump. It seems the copper wires attached to the brushes were rubbing on the armature, that shredded a lot of the copper. I'm guessing the armature was not installed properly and was causing the fuse to blow. Im sending back the motor for a replacement, I hope the company I got it from covers it.

Good. Glad you found the smoking gun and went to the trouble of verifying the cause. Makes it worth my time in attempting to help you.

Mark

 

[rookie456]

Here's an update. The company I ordered the PTT motor from sent me a new motor. I installed the motor and I still had the same issue, when I pressed the down button, my fuse would blow. I looked at all of my wiring and could not find any shorts. I decided to add a solenoid for the down wire of the motor, that way the battery would be directly powering the down movement of the motor, and the down button on the control would power the solenoid. That solved my problem, no more blown fuse. Makes me wonder why previous years before my motor had a 2 solenoid set up, and mine is only supposed to use 1 solenoid, only for lifting the motor. Thanks for all the responses.