Mercury Outboard Switch Box Failures

[DGMAX99]

This looks like a pretty popular website for boating issues, Mercury Marine equipment for this particular question, so I thought I would signup and post!

What would the most probable cause be for the inner mounted Switch Box on a Mercury 175 HP outboard to repeatedly fail?

I have a 1980 Mercury Marine 175HP V6 outboard (S/N 5489172) which suffered two Switch Box failures within a couple trips out on the water recently. This motor has seen freshwater only. I replaced the first Switch Box several years ago, but the boat sat for approximately 10 years without being used. I also replaced the idle control and coil wiring during the first replacement due to wire insulation degradation (a common problem on the year range). I don’t remember exactly how much time was placed on the first replacement Switch Box, but the boat was used quite often around the time I replaced it. Flash forward to today, I put the boat back in service recently after the 10 year storage period, and after about 3 trips out (~2.5 hours run time each), while idling, the motor dropped power and would not accelerate onto a plane. After limping back to my pier, troubleshooting found the there was no spark on the right back of cylinders (#1, 3 and 5). Swapping the inner and outer Switch Boxes around confirmed the no spark condition followed the faulty box. After inspecting all the wiring, grounds, stator/trigger resistance checks and whatnot (everything checked within spec cold), I replaced both boxes with a (used) pair and the motor ran great, for about 3 trips out at which time the motor started missing while under power (I thought it might have gotten water in the gas based on the way it was acting). It did clear up long enough to get back home, but after sitting a week, it did not have enough power to plane out again. Troubleshooting again confirmed cylinders 1, 3 and 5 are not firing.

Before replacing the Switch Box again, I thought I would see if there were some lessons learned out there. A little internet research did confirm that there appears to be a large amount of Mercury Switch Box failures, but little information concerning the possible root cause. Thanks!

 

[Dukedog]

Re: Mercury Outboard Switch Box Failures

They are prone ta go south for no apparent reason. Best ta be replace in pairs. Go with tha Mallory boxes. Buy two for tha price of one Merc. with a warranty............Lotta folks goin' ta these. Tried and proven ta be a good box. Even on some of tha "stem windin' " hot rod motors..........

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

To me it still seems odd that 2 would fail within a couple months of each other... I have to admit there seems to be an awful lot of posts/threads in cyber land about faulty mercury switch boxes tho. Maybe a poor design? Or something that feeds the boxes causing the failures? Stator? Trigger?

:grumpy:

 

[wired247]

Re: Mercury Outboard Switch Box Failures

I feel most outboard electrical problems are caused by bad batteries, discharged batteries or bad connections going to the battery. Keeping your battery on a trickle charger is the best thing you can do for all of your sensitive electronics. When the stator or alternator have to work full boogie to charge up a dead battery that has sat over the winter, it doesnt help the switch boxes that are running on too low of a voltage or the stator that is running on too high of an amperage playing catch up.

Mine are 17 years old on my 150. They work fine. Yours are 33 years old. How long are they supposed to last?

 

[Faztbullet]

Re: Mercury Outboard Switch Box Failures

If idle stablizer is still in use chit can it as it can mees up the bias circuit in switchbox and that will take out a box, but surpise the one that is usually workin is the one with bad bias and damaging opposite box.

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

I feel most outboard electrical problems are caused by bad batteries, discharged batteries or bad connections going to the battery. Keeping your battery on a trickle charger is the best thing you can do for all of your sensitive electronics. When the stator or alternator have to work full boogie to charge up a dead battery that has sat over the winter, it doesnt help the switch boxes that are running on too low of a voltage or the stator that is running on too high of an amperage playing catch up.

Mine are 17 years old on my 150. They work fine. Yours are 33 years old. How long are they supposed to last?

First, I just purchased my battery a couple months ago. It stays on trickle charge when not in use. Based on the voltage gauge in the boat, the battery tops off faily quick after running for a short time (output voltage indicates max output). My outboard is also carbureted so there is minimal load on the battery/charging circuit once running.

Just for clarity on the Switch Box age, 1 of mine is 33 years old and still works fine. The other original one (inner box) I had to replace sometime back in the 90s, if I remember correctly, that replacement went bad a month and a half ago. I then replaced both (keeping my 1 good original as a backup/spare). After replacing both, the inner box failed again after a couple trips out on the water. Just seems odd that my inner box keeps failing. Would be nice to know "what" is failing within the boxes, which I imagine contain typical discrete electronc switching components that typically have long life spans.

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

If idle stablizer is still in use chit can it as it can mees up the bias circuit in switchbox and that will take out a box, but surpise the one that is usually workin is the one with bad bias and damaging opposite box.

Interesting you mention the idle control (mine is still in place), while pulling the stator last night, I got to thinking about the influence the idle control has on the switch boxes. Appears it taps off the outer box high speed stator coil input, and then inputs both switch boxes on the extreme left top terminal (?WHT? designation). I did have to replace the leads up to the control box many moons ago due to the insulation degradation, but being encapsulated, I could only get the new wires as close as possible.

What are the affects if the idle control is removed?

Has anyone tied the idle control to the switch box failures?

Since the idle control basically jumpers to the ?WHT? terminals on both Switch Boxes, wouldn?t/couldn?t it influence both boxes the same?

 

[CharlieB]

Re: Mercury Outboard Switch Box Failures

The idle stabilizer controls idle speed by varying bias voltage to increase/retard ignition timing. When the stabilizer goes bad it increases timing at high RPM, sending rods out the side of the block. Remove it. Period.


There are a few things that contribute to shorten switchbox lifetime.

Poor ignition switch allowing any battery voltage to feed into the black/white kill wire.

Low resistance ignition coils. Test ignition coils to be sure all are within factory specs.

Heat, remove the mounting screws, replace with longer screws and spacers to increase distance from motor to inside box, and again to increase distance between boxes. This will improve airspace cooling of the inner box.

Use CDI switchboxes, they are far better than any others.

Your old bad bias boxes will work fine on any of the 3 cyl motors 75 - 90 HP. Mark them Bad Bias and sell them.

 

[wired247]

Re: Mercury Outboard Switch Box Failures

Switch boxes should be changed in pairs on V6 motors.

When you remove the idle stabilizer ( and you should ) make sure to reset your timing on the high and low side.

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

The idle stabilizer controls idle speed by varying bias voltage to increase/retard ignition timing. When the stabilizer goes bad it increases timing at high RPM, sending rods out the side of the block. Remove it. Period.

There are a few things that contribute to shorten switchbox lifetime.

Poor ignition switch allowing any battery voltage to feed into the black/white kill wire.

Low resistance ignition coils. Test ignition coils to be sure all are within factory specs.

Heat, remove the mounting screws, replace with longer screws and spacers to increase distance from motor to inside box, and again to increase distance between boxes. This will improve airspace cooling of the inner box.

Use CDI switchboxes, they are far better than any others.

Your old bad bias boxes will work fine on any of the 3 cyl motors 75 - 90 HP. Mark them Bad Bias and sell them.

The more I think about it, the more I am beginning to think the Idle Stabilizer may be a contributing factor, if not the cause. During this last escapade, the motor did sound like it may have been suffering detonation intermittently while under power. But it also seemed to be doing it just above idle. This was right before the extreme loss of power attributed to the odd cylinders not firing. I plan on taking the suggestion to remove the stabilizer completely, and then do some retesting.

Will the timing need to be reset if the stabilizer is removed? (I have read threads that stated both ways, some say adjust it, others say it is not necessary)

What if it still idles fine?

Interesting comment on the old switch boxes. Is there anyway to test them without having a 3 cyl available to install them on?

Is it the white wire link between the boxes (when installed on a 6 cylinder) that creates the issue?

What happens if a 6 cylinder is started with the white wire link removed? (just to check for spark)

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

Switch boxes should be changed in pairs on V6 motors.

When you remove the idle stabilizer ( and you should ) make sure to reset your timing on the high and low side.

I think you answered one of my questions to CharlieB at the same time I was posting it! Any suggestions on how and what to set the timing to?

 

[wired247]

Re: Mercury Outboard Switch Box Failures

Idle timing is going to be dependent upon whatever RPM your idle is. I usually set mine at 800 RPM in gear. That way it kicks up a bit in neutral and doesnt stall on a hard stop. Max timing should be 23 or so.

 

[Faztbullet]

Re: Mercury Outboard Switch Box Failures

Your outter box is bad and damaging inner box. Omhs spec for bia's is 14000 ohmsfrom white/blk terminal to box case.

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

Your outter box is bad and damaging inner box. Omhs spec for bia's is 14000 ohmsfrom white/blk terminal to box case.

All the boxes I have check around 14K ohms from the bias term to case ground, (the "WHT" top left terminal when looking at the box face, 4 horizontal terms at top). This includes the ones I replaced to get it to run on all 6 cylinders again, and the ones that do not want to fire now. When I replaced both boxes a few weeks ago I documented the ohm readings to ground at all terminals, along with a few other values. I rechecked them tonight and they read the same (this is with the boxes removed/completely disconnected from the motor.

I also pulled the stator and trigger from the motor to do a visual inspection, everything looks OK. Also rechecked all the ohm reading for both, all are within spec.

I have completely removed the idle stabilizer and plan to leave it off, but with everything else checking within spec, I'm not sure what to replace now...

 

[Dukedog]

Re: Mercury Outboard Switch Box Failures

To me it still seems odd that 2 would fail within a couple months of each other... I have to admit there seems to be an awful lot of posts/threads in cyber land about faulty mercury switch boxes tho. Maybe a poor design? Or something that feeds the boxes causing the failures? Stator? Trigger?

:grumpy:

Just something ta think about for ya. Do you read anywhere on tha "internet" about tha "thousands" of any given part on older V6 (including oil injection stuff) Merc/Mariners still runnin' just fine. Old stuff (newer stuff too) is gonna break and/or give up at some point in time especially in tha Marine world.............

But tha Mallory boxes seem ta be a cheaper, better/newer design...............jmo

 

[CharlieB]

Re: Mercury Outboard Switch Box Failures

When a spark test fails on one side of the motor, disconnect the Bias wire and retest. If spark is restored then the box that WAS sparking has a bad Bias circuit and is blocking spark on the other box.

IF, these are CDI boxes it is allowed to replace only the one box. ALL other brands it is recommended to replace both boxes.

Ohm tests are not always the most reliable indicator.

Cranking and/or running tests using a DVA meter are the most reliable and highly recommended.

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

When I replaced both boxes a few weeks ago I did check the voltage outputs/inputs and found them to be as expected/in spec. Everything was working at that time tho, and the motor was running great. However I did not check the idle stabilizer input to the boxes to see what it was doing.

I think I will try lifting the jumper between the bias terminals on my latest set of switch boxes (maybe even my old original boxes) and see what happens. If this works, I should be able to pair-up and install the two boxes that appear to be dead (no spark) and the motor should run. On another note, it seems like if the idle stabilizer is removed, then the bias terminals would need to be held at some stable know value to prevent them from “floating”. Leaving the jumper just ensures both bias circuits are at the same value at any given time. Without a schematic or being able to “see” into the box circuit, there is not much of a way of knowing if there is some sort of electrical (internal) tie that keeps them at a stable value across the RPM range, which opposed the idle stabilizer input signal when it was installed.

While I have the flywheel pulled and access to all the electrical/electronic parts, I have decided to renew everything in hopes of making the motor reliable again. It is no fun to be out on the water when a motor fails to operate properly! Although the stator and trigger check within spec, as Dukedog pointed out, they are ~33 years old, although the last pair of switch boxes I installed were a newer version than my original 332-5524A1 boxes. I have a new CDI trigger and stator on the way but may try a new set of Mallory switch boxes as the warranty is a little less restrictive. The CDI warranty specifies that their switch boxes must be installed by a “professional marine technician” for them to honor warranty claims.

I still don’t totally buy that the switch boxes are just “prone to failure” for no apparent reason. There is always a “reason” something “fails”, (even new components have an “infant mortality” rate that is recognized/understood), and there just seems to a wide range of switch box revisions that fail in a similar manner. Just wish I had a circuit schematic so I could understand the circuit interactions a little more (I have an electronics degree and have worked in the field for 35+ years).

 

[Dukedog]

Re: Mercury Outboard Switch Box Failures

.


I still don’t totally buy that the switch boxes are just “prone to failure” for no apparent reason. There is always a “reason” something “fails”,

That is tha "key word in tha Merc/Mariner switch box (and/or most electrical parts) dilemma. Its really not that complicated ta tha majority of folks workin' on these things. They check bad, replace and go on down tha road. But I do understand, with what you say is your expertise, why it would be questioned..............I'm sure there's a schematic out there somewhere. Just don't care enough ta do tha research ta find it.......
I do know this though. Have a few A1's (really old) that are still runnin' and a bunch of A12's, A14's and A15's in tha junk pile. Go figure...............

 

[DGMAX99]

Re: Mercury Outboard Switch Box Failures

I spent a little time yesterday checking and rechecking everything, including each switch box I now have, 5 total. Three boxes are now basically confirmed dead. I installed each one with a switch box that does provide a spark to its associated bank, without the bias link connected, and three would not produce a spark. This was after I confirmed the problem did not following the stator red-blue, red/wht – blue/wht circuits. I also check the kill circuit to each box and each was observed to give a solid open circuit when the key switch was on, and ground when off. I then installed my one good 332-7778A12 box with one of my original 33 year old 332-5524A1 version boxes and had a good solid spark on all 6 plugs (with bias link still disconnected). However I did not take it out on the water for a run, just too sketchy with the differences in the box versions. All this testing was completed with the original stator and trigger, but with the idle stabilizer removed.

I have now replaced the stator and trigger with new CDI Electronics components and will be ordering 2 new switch boxes on Monday. Once I get those installed I will reset the timing and see what happens, without the stabilizer. I do think I will try two Mallory boxes tho, they appear to be a little more lenient on there warranty coverage, CDI will only cover there products if a “professional marine technician” installs the parts and you have record of it. A little hard for me since my boat pretty much stays on a cradle at my pier. Also hard to pay more for a product and the vendor not cover the warranty period because I installed the part myself. As I indicated before, my whole career (35+ years) has been in electronics and mechanics, the majority of which has been in nuclear power at that, I have no problem installing and testing these components. But it appears CDI would not care about that… Besides, it appears others have had good luck with the Mallory boxes.

Still not sure about the “root cause” but by renewing everything maybe the motor will prove reliable again. Sure hope so!

Thanks for all the help! I will let everyone know how it works out.

 

[CharlieB]

Re: Mercury Outboard Switch Box Failures

The O/B ignition switch is a double pole switch, one side handling the 12V circuit, the other the simple open/close of the 'ground-to-kill' ignition.

Over sufficient time mineral accumulation from water intrusion and evaporation can cause an intermittent 'bridge' between the two switches.

It does no occur with every turn of the switch, but one those rare occasions that it does, and DC current 'leaks' into the kill wire, it damages the switchbox.

I've had occasions that it took me 60 turns of the key before I registered voltage on the kill wire terminal of the ignition switch.

So I have to ask, how OLD is your ignition switch?

If you are willing to invest enough time, disconnect the kill wires, rig your meter to the b/y term at the switch, have sufficient libations within reach, and start exercising the switch to see if you get a reading.