'73 mercury 1150 inline 6 rectifier issues

[JustinHerlyn]

It's been awhile since I've posted, so hopefully I did this right.

I'm trying to figure out a rectifier issue with my dad's mercury 1150. He accidentally made the mistake a couple weeks ago of touching the battery cables together. He realized something was wrong when he tried to fire the motor and had no spark. we tested the rectifier, and sure enough, it was bad. So for good measure we ordered CDI replacement parts for both the rectifier and the switchbox. We figured seeing how they were both 40+ years old, we would just replace both of them.

Well, with a little bit of work, we got both new parts wired in. The switchbox was a little challenging due to it being a universal part, but I do this with boards on furnaces all the time, so this wasn't my first rodeo. Got it all wired up, and we had spark. Problem solved, or so we thought.

The next day, we go to turn the motor over. it tries to turn, even to the point of disengaging the starter, and then dies. That's nothing new for this mercury, which has always seemed to be a hard starting, cold blooded SOB. It does this three times, and on the fourth try.....nothing. we try starter fluid.....nothing. So we pull the plugs to check spark. it's gone again. We test the rectifier, and it's bad, again.

This is where I'm stumped. I have checked all the wires coming into the motor, cutting the tape around them and pulling the harnesses. everything looks good. I checked the battery cables, both battery side and motor side, they look great. Tested the CDI switchbox per the instructions from CDI. It tests out great. The only thing I found wrong was the brown wire on the four terminal side of the old switchbox was in need of replacing, but after researching it, I'm under the belief that wire is only a tach wire. I even tested the battery, and it's good.

So I don't know why this motor keeps frying rectifiers. And I don't want to keep throwing rectifiers at it. So my question is why did it fry the rectifier the second time? Could it have been that tach wire? Could there be something wrong in the wires coming from the remote control causing It to fry the rectifier? Is there something I'm overlooking? Any help would be greatly appreciated.

Thank you.

 

[Georgesalmon]

Under the flywheel is the stator. It supplies AC voltage to the rectifier. Check it out, might be open or shorted. Two yellow/red stripe wires. Unhook and use an ohmmeter. The brown is probably the tach signal, I've seen over the years brown, tan, and grey all used for the tach signal at some point in time. There is really not much interconnection between the rectifier and ignition. The stator supplies AC to the rectifier and the tach signal, then the rectifier recitifies and you get DC to the red wire (this red wire and ground are the only things common to the rest of the motor). You don't even need the stator or rectifier for the plugs to fire and motor to run as long as the battery is good. It's not uncommon for the stator wires to get brittle and break or turn green inside or the magnets to get weak or even fall off the flywheel in these old motors. Google a wiring diagram if you don't have manual there is a bunch of them out there and easy to follow.

 

[Chris1956]

If the rectifier becomes disconnected from the red battery wire, it will be damaged. So, you need to make sure that red wire is clean and tight. It also provides steady power to the switchbox as well, so it is doubly important.

You do have the -DC post of the rectifier grounded, right?

 

[JustinHerlyn]

I haven't run any checks on the stator, I suppose this could be a problem. Lord knows it was on my '75 Evinrude. Replaced the stator, and boom....it just ran perfect. But this motor has a distributor, and the flywheel runs a belt, so I don't think it has a stator like you're thinking, does it?

As far as having spark without the rectifier, we didn't have spark and the rectifier was bad the first time. we then replaced the rectifier and spark was back, although for only three attempted fires of the motor. And it did turn over like it had good spark on all six cylinders, it just didn't keep running. I even talked to a local boat mechanic shop before ordering the rectifier the first time, and he bet dollars to doggy doo that the problem was a bad rectifier that was leading to no spark. I'm not trying to say you're wrong about being able to have spark without the rectifier. If there is a way to bypass the rectifier to test for spark, it would be helpful, so let me know. Like I said, I'm truly stumped.

Chris1956, The old rectifier's DC post wasn't grounded in a wire sense. There's only three posts on the rectifier, two yellows and a red (DC) post. I assumed the rectifier was grounded by being mounted to the metal frame of the motor, not by the posts. Am I wrong? Could even a weak ground cause issues? The old rectifier bolts and the new ones didn't quite match up, so we kind of had to rethink the mounting. I'm wondering if the screws I used didn't ground it enough. Is that possible?

 

[Georgesalmon]

If there is no stator, where do the yellow or yellow/red wires supplying AC voltage to the rectifier come from?

 

[Georgesalmon]

If there is no stator, where do the yellow or yellow/red wires supplying AC voltage to the rectifier come from? On your old evenrude the stator was also the trigger. On this merc the stator is only used for charging the battery.

 

[Chris1956]

Justin, On your Merc, there is a very simple stator. It has just two wires and charges the battery, by converting the AC voltage to DC voltage at the rectifier. Both the original rectifier and any replacement rectifier will have 4 posts. The OEM rectifier had the -DC post internally connected to frame ground, by the bolt. A new rectifier could have 4 visible poles. If so, you must take a piece of wire and ground the -DC pole to frame ground.

The battery voltage supplied to the switchbox provides the spark. The rectifier is separate and has no impact on this. The only common connection to both is the red battery wire, which is hot all the time. There is a scenario, where the rectifier shorts from +DC to one of the AC posts. If the red battery wire is a marginal connector, in theory, the shorted rectifier could drop the voltage to the switchbox, killing the spark. I would disconnect the rectifier (all posts), to isolate this issue.

 

[BatDaddy1887]

....may be a simple answer but how about checking the kill switch/lanyard and the 20amp fuse at the engine..........

 

[JustinHerlyn]

So I tried your test, Chris. I pulled off all the wires on the rectifier and tried to turn the motor, and there is no spark. But just because I'm stumped and literally obsessed with this problem now, I looked in the manual for the motor that I have. I'm reading the flow of energy section, and it states:

"The flow of the energy from the battery to the spark is as follows: The energy runs from the battery into the switchbox, where it is inverted to AC Power. It is then sent to strengthen the AC power, and is then rectified and stored in the capacitor of the switchbox, where it awaits a triggering signal."

Now to me that reads that the rectifier is an essential part of the process. No rectifier, no spark. But I could be interpreting it wrong. Am I? I only have three triggering wires and six cylinders, so the trigger wires must each fire two cylinders, which would make sense as to the use of a capacitor. It eliminates the need for six direct firing magnets or coils.

As far as a fuse, all the fuses I can find seem fine. And when I tested the switchbox per the CDI instructions, I was getting the mandatory 9 1/2 volt minimum readings on all wires. So to lose the voltage between the switchbox to the rectifier, per the book's flow of energy, I would have had to blow a fuse between them, which there doesn't seem to be any.

So anyway, my Dad, being the eager one he is, has already ordered another rectifier. It should be here Monday. Until then I'm kind of dead in the water. I was just trying to figure out why it would have worked and then stopped working so quickly. To me, something else must've gone wrong. I really appreciate everyone's input. Hopefully if we keep banging our heads together we can find a solution.

Please, any more ideas would be nice, I'm trying them. Eventually something should pan out.

 

[Chris1956]

Justin, Your description is discussing the rectifiers internal to the switchbox. It is not talking about the external rectifier that charges the battery.

Leave the external rectifier disconnected and run the CDI Electronics ignition test for your "Battery Powered CDI Ignition". It is found on the CDI Electronics web site. It will isolate the trouble to the switchbox and wiring, and the trigger.

You do have +12VDC on both the red and white (non-distributor) wires to the switchbox, right? If not, you will not have any spark.