TOPIC: Things to know about your charging and ignition

Hi,
Read the post about the Merc 1500 overcharging. I found out some interesting info I was unaware of in regards to selection of battery and potential switchbox damage. It cost me $$$ before finding out problem so save yourself the aggrevation and expense.
Anyone using an older Merc outboard Thunderbolt ignition should read it.
Randy

Randy did your switchbox get fried? I use the old big lead car batteries, so they must absorb most the extra charge.

Was looking at smaller batteries for my 1500 and my fast boat . Might not be a good idea. I use cheap lawn mower batteries from walmart, but they last about 1.5 years.
Conrad

Hi Conrad,
Yup it fried, two of them actually. Motor would still run but it is rough and does not rev out. I could also hear a clicking sound, like a high voltage arc coming from them when damaged. Originally whn motor started running rough I deduced it was the switch box even though it was new, maybe it had an issue to beging with, when I switched it out all was fine till after a few flawless high speed runs it started missing again. Now,I thought I grenaded a cylinder on a brand new rebuild, comp check said all was fine..whew. Well where the switchbox was swapped out I thought I discovered yet another weak ignition part, this time I thought coil, so I replaced that. Still the same miss fire running, then on further inspection, I notced the ferrite on the coil was cracked so I bought a new coil, still same issues.
So I backtracked knowing the probelm seemed to be linked to high RPM operation where ignition is stresssed the most. I made sure all high tension wires were good, plugs good, cap good, rotor good, trigger good, coil brand new, which brought me back to the Switchbox again. So I swapped out for another switchbox (3rd one) and all was good (again) Now I was thinking that I am damaging the switchboxes somehow, maybe the charging system was putting out high voltage or was producing a voltage spike at high RPM, these charging systems output proportional to RPM So I measured the voltage output with my hand held and output was high. I surfed the internet and found several helpful posts on different forums, I also talked to a technician at CDI.
I found out that you are pretty much gauranteed to hurt a switchbox when it sees voltages over 16 volts, (mine were) and there are many people experiencing high volt charging on their Mercs. This is when I learned about the importance of the battery type used on these unregulated cahrging systems.
I had installed a low maintenance battery so that turned out to be my problem, I now have the standared lead/acid/vent cap style battery. Voltage is in check now...who woulda thunk??!
If you want to run other batteries I would install a voltage regulator in combo with a rectifier. CDI has one to do this and some later Merc V-6's have the same part that combines regulator and rectifier. That is the bullet proof solution, I am remembering that the good Dr. walked Frank through this on his 1000. Frank, I think, had an accessory that needed regulated voltage, his motor was old enough with no switchbox. I am trying to keep my motor close to stock original so I swapped the battery out. My ski boat has a regular automotive alternator so it does not care what battery it has so I just swapped batteries between boats.
I hate to say it but the two switchboxes that blew up where prized possesions, one was NOS for an XS (DAMNIT!!) and the other was a stock NOS (DAMNIT AGAIN) I run about 6000 rpm so I am not hitting the stock rev limiter on the used stock box that the motor has now, so it runs great.
In the end I'm just happy after 2 1/2 years of restoration work to be back in the Hydrostream enjoying the water and forget about the bitter pill of wasted parts for a stupid reason. Some things are just not easy.
Randy

Randy,
To control the voltage output I install a Merc v6 regulator, part number 883072T or Sierra Marine number 18-5743.
These have a rectifier built into them so the original rectifier would be removed from the Merc.
These cost between $110-$150 on line, but used ones can be snagged off eBay for around $40-$50. They rarely fail, so used is a good bet and some vendors that are outboard salvage businesses will replace one that is no good upon install, but be sure about that before buying. I buy from these guys:
service@boatmotorrecyclers 'dot' com
I see that the inline-6 switchbox A23 appears to have gone NLA, but an A27 off a 4 cyl Merc will work, except that the tach terminal (brown on starboard side) will not send the correct signal to an original Quicksilver Tach, so a tach that reads off the stator would need to be used.
I am not positive, and recommend checking with CDI/Rapair, but it is my understanding that their replacement switchbox and coil (all in one unit) 6 cyl part number 114-2803 does not have a rev limiter installed.
CDI Electronics Tech Support 1-866-423-4832
Thom

Where does a standard brain box rev limit at?

My XS box was toast when I got the motor. I took a box off a non running 1974 1500 and it ran, and I have pulled close to 7000 RPM with that box.

Are there part numbers for what boxdoes what?
THanks
Conrad

Hi Conrad,
The XS switchbox has a different dash number on the end two digits.
I was told this was due to a different Rev limiter. I have only run my stock 1500 up to about 6200 RPM and run the XS with the XS box to about 6600. In either case I have never bumped a rev limit. So your experience with even higher RPM and the stock box is more meaningful than mine.
I for sure have no idea where the rev limits are. I'm glad you can rev that high with a stock box becasue I was fearing that if the XS one blew up I could not run my XS at the needed RPM.
Here is what I understand, don't know if it is right. When Merc eliminated the mercury tilt switch, my thought was they introduced the rev limiter to prevent damage on an over rev if the motor struck something and tilted up out of the water. This would also explain the rumor that the earlier "green" boxes have no rev limiter as those earlier motors depended on the mercury switch to kill the ignition so no rev limiter was needed. Where the XS was made to satisfy class racing adn the higher RPM associated with that endevour it seemed logical that a higher limit (or none) would be used in the switch box.
I guess your experience says that the rev limit on a stock box is pretty high anyways, so maybe the XS one just eliminated this feature altogether.
The switch box part numbers are all the saem except for the last two digits. A stock box is 332-2986A21 an XS or (short shaft box) is same number ending in 25 not 23.
Randy

The box I took off my 1500 Long shaft that I am running 6900RPM is part number 3322986a21 . I think it was a replacement at some point because the 1500 Long shaft originally came with 33232986a21.

The 3322986a21/3322986a4 is the latest one and is still available for $523.09.

MY 1500JXSSHORT motor box came with a different sticker on the back of it. It actually has a blank line to fill in the last two digits and a line that says RPM. Neither box is filled out. It reads p/n 332-2986a___ RPM_______ None of my other boxes have an RPM space. I wish this one was filled out.

Next is a part number list that I looked up for each motor.


1250,1400, 1100ss, 1150, 1000SS, 1350, 1400
still available 3322986a4/3322986a21

1500LONG NA 33232986A21

1250BP NA 3322986a7

1000BP NA 3322986a9

1500 xs NA 3322986a25

I assume all switchboxes can be replaced with 3322986a21 that is still available.

I hope Im not loosing power up on top that I dont know about due to a switchbox not able to handle the RPM.

Conrad