Mercury 135 Black Max repeat switch box failures

[ikessky]

I bought a 1992 Alumacraft Trophy 180 with a 135 Mercury Black Max (the seller said the motor is a '93) in the spring of 2021. We fished, we rodded around, we tubed with the kids. Went fast and had a great time. Although I did notice that the tach was either way off or there was something bad with the motor since it said I was at 7k RPMs..... One the second to the last outing of the year, I made a hard turn and felt a loss of power that then kicked back in and after about a minute, I was getting the low oil beeping alarm. I limped it back to the dock, but never got around to fixing it.

2022 saw a job change a few vacations and I never took the boat out once.

2023, I completely redid the console and got all new gauges. I did some research and ultimately found that the low oil alarm was due to the outside switch box being dead (confirmed I wasn't getting spark on one bank). On recommendation of some forums, I replaced it with a Seirra box and ran the motor on the muffs. Started right up, ran great, I was happy! Took the boys out fishing, rodded around the lake a little bit (the new tach showed I'm at about 5k RPMs) and came back home. My next outing a week or two later, I get the boat in the water and fire it up and it's immediately running rough, then the oil alarm starts in again. I head back home and find that the brand new switch box is dead. I decide to take it to the local Mercury dealer and tell them I'm concerned that something else is causing the boxes to fail. They call me back a few hours later and say it's a dead switch box, we put a new one in, it's good to pick up. While I was there, they tell me that they "looked" at the stator and it seems fine. They are either good or bad. They see brand new boxes that are bad out of the package all the time, should be good to go. No need to replace both of them, just the dead one. When I got home, I did check to make sure that there was no voltage going back to the kill wire from the key switch, another recommendation from some forums.

So here's where I'm at..... I'm honestly scared to take this back out again. We've got some great lakes that are 30-40 minutes from my house that would be fun to take the family to, but am I going to get all the way there and offloaded only to be forced to rely on the trolling motor to putt around? Is there anything more that I should be replacing? Is this Mercury tech a crackpot and I need to find someone else?

[LakeFever]

Man I feel this one. In the end my solve was replace both switch boxes, new stator, and new ign switch. That boat went from one day great to next day no start to one day flying to next day a dog until i made the whole parts install. After that it ran so good, really great motor.

Iirc the consensus is you should change switch boxes in pairs. I believe theres a way to test them to make sure they are both in the same range but you’ll have to search that out or maybe someone else will chime in on how to do this. Probably overkill for your motor. Im sure if you replace both switch boxes and the stator and make sure you dont have the water cooled regulator too thats a known trouble maker. Also if you have them do a black box delete and finally switch to premix and get away from the oil injection. I paid that piper once too by ignoring the same advice.

hope some of this helps ya out

[skialot2]

I would change switch boxes in pairs if I were using new boxes. If using used i would not mix brands. I would never use a Seirra with an OEM box. That being said, the biggest killer of switch boxes is a bad ground. It is not enough just to bolt the box to the bracket. Make sure the little black ground wires are there and in in good condition. A bad ground will kill a switch box very quickly.

[ikessky]

Through a series of events, I now have two spare boxes. Unfortunately, one is a Sierra and one is a CDI. Obviously I have to get a matching box, so which one do I go with?
If I would choose to just change the stator, is CDI the brand to go with or get an OEM Mercury?

[pcrussell50]

Through a series of events, I now have two spare boxes. Unfortunately, one is a Sierra and one is a CDI. Obviously I have to get a matching box, so which one do I go with?
If I would choose to just change the stator, is CDI the brand to go with or get an OEM Mercury?

I have had equally good luck with both OEM and CDI stators. On either, you want the least electrical resistance in the yellow wires as possible, based on what I read here. If they have bullet connections, you might solder and heat shrink instead. That will help keep the yellow wires from overheating and cracking their insulation off.

Re switch boxes, another prominent SnF user swears by the made in Germany, Sierra switch boxes. Just make sure you get the real deal. The real ones will be $250+ each. The Chinese knockoffs will be $60 for two or $35-$40 for one. Now… Another SnF’er I know has the Chinese ones and they are working for him. The problem would be if they dual-fire… Could cost you the motor.

-Peter

[LakeFever]

Another worthwhile task is to remove and clean the carbs. I spray brake clean through all the orfices and holes making sure clean unobstructed flows spray through each. Inspect the needles and replace if worn. Many say always replace the neeldes and gaskets but with care ive had good luck reusing all if they are not damaged. Just have to be gentle during Disassembly so you dont tear any. You also should replace every single rubber hose and line on the powerhead. You can use tygon for the small ones, home depot sells all the sizes. The rubber hose can be bought at auto parts supplier although not marine rated. Not sure what the difference is on marine rated rubber vs auto store stuff ive used both cant tell a difference other than price.

Doing the above is time consuming but very low buck and will make for a much better running motor

[pcrussell50]

The rubber hose can be bought at auto parts supplier although not marine rated. Not sure what the difference is on marine rated rubber vs auto store stuff ive used both cant tell a difference other than price.

J1527 marine hose is supposed to be able to burn for 2.5 minutes, without letting fuel escape. This causes it to be a little stiffer and harder to work with in short runs with bends. But it might carry insurance implications if you don’t use it and need to make a claim, and liability implications if someone gets hurt and sues you. But in reality it’s not like properly certified SAE 30R7 automotive fuel line is junk. It’s not, of course. It all gets down to your level of tolerance for liability risk.

J1527 is for pleasure boats. There is another standard for commercial boats.

-Peter

[ChrisCarsonMarine]

The stater makes 250 to 300 V, that voltage is supplied to the Switchboxes, and stored in the capacitor, waiting for an SCR switch to send it out to a coil. The engine is shut off by turning off the key, which connects the Switchboxes capacitors to ground in the Key Switch. This causes an arc in the Key Switch, and sooner or later, conductive dust forms in the Key Switch,when this dust reaches a level that allows more than a half a volt to find its way to the kill wire, leading to the Switchboxes, it ruins the Switchboxes.disconnect The kills from the Switchboxes put a voltmeter on the kill wire and ground and measure voltage. There should be no more than 1/2 V during any stage of action on the Key Switch, on off or Crank. If there is, do you have found your problem , replace the key switch, Chris

[pcrussell50]

The stater makes 250 to 300 V, that voltage is supplied to the Switchboxes, and stored in the capacitor, waiting for an SCR switch to send it out to a coil. The engine is shut off by turning off the key, which connects the Switchboxes capacitors to ground in the Key Switch. This causes an arc in the Key Switch, and sooner or later, conductive dust forms in the Key Switch,when this dust reaches a level that allows more than a half a volt to find its way to the kill wire, leading to the Switchboxes, it ruins the Switchboxes.disconnect The kills from the Switchboxes put a voltmeter on the kill wire and ground and measure voltage. There should be no more than 1/2 V during any stage of action on the Key Switch, on off or Crank. If there is, do you have found your problem , replace the key switch, Chris

Damn. What rich post. Superb.

Do you have a rough idea how many on-off cycles an ignition switch is good for? Is it hundreds, or thousands?

Some old timer once told me, he stops his carb motors by flooding them out with the enricher. I was never sure why, but it was interesting.

-Peter

[ChrisCarsonMarine]

I'm sure its thousands,but dew,and rainy weather moistens the dust and makes it more conductive,Chris

[skialot2]

J1527 marine hose is supposed to be able to burn for 2.5 minutes, without letting fuel escape. This causes it to be a little stiffer and harder to work with in short runs with bends. But it might carry insurance implications if you don’t use it and need to make a claim, and liability implications if someone gets hurt and sues you. But in reality it’s not like properly certified SAE 30R7 automotive fuel line is junk. It’s not, of course. It all gets down to your level of tolerance for liability risk.

J1527 is for pleasure boats. There is another standard for commercial boats.

-Peter

We are talking about a 1992 motor. Can you actually get affordable fire insurance for a 30+ year old motor? I understand liability insurance. But fire insurance? I would think the premium would not be worth it.

[skialot2]

The stater makes 250 to 300 V, that voltage is supplied to the Switchboxes, and stored in the capacitor, waiting for an SCR switch to send it out to a coil. The engine is shut off by turning off the key, which connects the Switchboxes capacitors to ground in the Key Switch. This causes an arc in the Key Switch, and sooner or later, conductive dust forms in the Key Switch,when this dust reaches a level that allows more than a half a volt to find its way to the kill wire, leading to the Switchboxes, it ruins the Switchboxes.disconnect The kills from the Switchboxes put a voltmeter on the kill wire and ground and measure voltage. There should be no more than 1/2 V during any stage of action on the Key Switch, on off or Crank. If there is, do you have found your problem , replace the key switch, Chris

I have had several bad ignition switches cause all kind of running problems. I have found that Evinrude/Johnson motors are much more sensitive to the stray voltage you are referring too than the Mercury's. I am not saying it doesn't happen on Merc's. Just that OMC's seem more sensitive to it.

[ikessky]

I'll check the key switch voltage again as I was alone and couldn't switch while watching.
The weather is going to turn soon here, so maybe I just do the stator and a such over the winter months and start fresh.

[LakeFever]

When i had my mystery issues i chased it a whole summer one thing at a time. It basically ruined an entire season of boating. Then someone here said the motors 30 years old who knows whats wrong with it so change all the electrics to brand new in one shot and rule it all out. So thats what i did and that boat still runs tip top. Worth every penny to regain that piece of mind as well as all the fun boating. Just my two cents on this