Logo
FULL SITE MENU

bad switchbox or trigger on mercury 65hp 73-75 3clyinder.

J

jldsomething

New member
can anyone tell me how to tell the difference if my switchbox is bad or trigger?
i have no spark at all three plugs
its not coil i have changed that.
im getting power to switch box
wires are all fine i have checked.

its a 65 hp mercury year is 73-75 not sure. serial number starts with a 405.
i have tested all the manual will tell me and am at a loss i do not have dva tester only a automotive ohm tester.
most things i have read point to switch box because none of the 3 plugs are firing at all.
also the problem is intermediate it was starting and running then took a lake and wouldn't start back up then brought it home and it would start and went out the next day and it would not start.

i have tested switch box while trying to start and one white wire as hot as crankin over but no power going to the coil or other wire on the distributor.
 
its the distributor model. i was hopping it be the switchbox but im guessing its the trigger which i cant find used. i thought about jumpin the trigger wires on the switchbox and seeing if it will fire to tell me if its the trigger or switchbox i just didnt know if that would hurt anything.
 
It might be the trigger, but my money is on the switch box. The trigger is a very simple design that you can test with an ohm meter. It's either an open circuit or closed and, if closed, it should work, The switch box is another thing--you need a special deal to test it out.

Jeff

PS: That motor is one of the few Mercs that require battery voltage to run. Be sure to check for it and a good ground. I suggest jumpering out the remote control harness and see if that helps. Could be a bad ignition switch/ connector.
 
Well I just did the switchbox test from cdi electronics and the switchbox tested good. Do you know how to test the trigger or keyswitch ? At this point I'm leaning towards a triger but I would like to rule out the key switch first before I blow 200 on a trigger thanks
 
I have the same motor and the same issue and result. How would you perform a continuity test on the trigger? I'm stumped and would love to get this motor running. TIA
 
The above info is incorrect as its more like a Hall effect unit. Disconnect the mercury tilt switch first and if no spark check your voltage on the red and white Ignition wires at the switchbox. If the voltage is less than 9 1/2 volts on both when cranking the problem is in the battery,switch,wiring or switchbox. These units require at least 9 1/2 volts to fire properly. Check the voltage on the wht/blk terminal and you should see at least 9V at cranking. DVA check between black and blue and you should read at least 2 1/2 volts at cranking. If voltage is low connect a jumper Wire directly from the battery POS (+) terminal to the red and white switchbox wires!! DO NOT Connect the jumper Wire To the WHITE/BLK Trigger Terminal!! If it fails any of the above trigger tests trigger is bad....
 
faztbullet said:
The above info is incorrect as its more like a Hall effect unit. Disconnect the mercury tilt switch first and if no spark check your voltage on the red and white Ignition wires at the switchbox. If the voltage is less than 9 1/2 volts on both when cranking the problem is in the battery,switch,wiring or switchbox. These units require at least 9 1/2 volts to fire properly. Check the voltage on the wht/blk terminal and you should see at least 9V at cranking. DVA check between black and blue and you should read at least 2 1/2 volts at cranking. If voltage is low connect a jumper Wire directly from the battery POS (+) terminal to the red and white switchbox wires!! DO NOT Connect the jumper Wire To the WHITE/BLK Trigger Terminal!! If it fails any of the above trigger tests trigger is bad....
Click to expand...


Thank you very much for this info.

Following your instructions, (the first thing I did was disconnect the tilt switch wire). I got 11+ volts on cranking at the red and white wires at the switchbox. Voltage at the wht/blk was also 11+. I don't have a DVA but with the other two test being positive, would that be neccessary? I did jumper them when performing the switch box test and the had healthy spark.

I had the flywheel off and the distributor off. I'm going to reassemble and static time the ignition as I think that's what might be amiss if all these other tests are passing. The leads all check out from coil to distributor and dist to plugs for continuity, although old, I will be replacing them as well. I did reattach the distributor but not the belt, so don't know if there is any spark at the distr.

I don't have the timing stickers on the flywheel but made reference marks before I disassembled everything. I will update the thread very soon.

Thanks again!
 
Should I attempt to disconnect the forward controls and start the motor with a remote starter with the white and red jumped on the switch box?

Could there be something on the control box that is stopping it like the neutral start switch? There is no kill switch lanyard on this.
 
A neutral safety switch prevents the starter from operating--it doesn't kill the ignition.

It sound like either the distributor is shot, or the switch box is dead. Both are hard to find used and expensive to replace with after market parts. Just went through this with a similar Merc; I converted it to the later ADI ignition system (which took a lot of work and spare parts). Sorry.

Jeff
 
fastjeff said:
A neutral safety switch prevents the starter from operating--it doesn't kill the ignition.

It sound like either the distributor is shot, or the switch box is dead. Both are hard to find used and expensive to replace with after market parts. Just went through this with a similar Merc; I converted it to the later ADI ignition system (which took a lot of work and spare parts). Sorry.

Jeff
Click to expand...

I did the switch box test and it passed. So yeah, it sounds like the distributor.
And yes, it's expensive as hell. I'm searching for a used one and it's a unicorn hunt.

Thanks for all your help.
 
I did want add that I did the continuity test above and got 34ohms on the body to the trigger wires. I don't know what the specs are.
 
I think at this point, I have nothing to lose with the distributor. I can't seem to find any instructions on how to disassemble this and perhaps take a look at trigger by melting away the epoxy. There are no visible signs of corrosion on these wires so it might be internal.

Thanks everyone.
 
Probably. If you tear into it, let me know if you find anything wrong in there. I have a similar, 4/ 6 cylinder distributor that also tested okay but is dead.

Jeff

PS: Since replacements for this type are so dammed expensive, my this Winter's project is to modify one of these distributors to use an HEI module out of a GM car to fire automotive type coils. The timing disk will be replaced by a spiked wheel to trigger the module, that will be mounted inside the distributor with the guts milled out.
 
Last edited:
fastjeff said:
Probably. If you tear into it, let me know if you find anything wrong in there. I have a similar, 4/ 6 cylinder distributor that also tested okay but is dead.

Jeff

PS: Since replacements for this type are so dammed expensive, my this Winter's project is to modify one of these distributors to use an HEI module out of a GM car to fire automotive type coils. The timing disk will be replaced by a spiked wheel to trigger the module, that will be mounted inside the distributor with the guts milled out.
Click to expand...

I will definitely let you know my results.

I was thinking the exact same with replacing the internals with automotive parts. It seems doable.
 
I apologize for my constant posts. Being new to marine with a mechanical background in auto and small engines and motorcycles is helping though. I just want to make sure that I've performed all the tests correctly and that I can move on to next steps as I've found a used distributor for this exact engine but the price is dear.

The coil and switchbox tests were performed using this instruction -
https://www.youtube.com/watch?v=9E8PN_dL5Rc

The coil is also new but the old one passed the test as well. New one is still installed.

----------------------------------------------------------------------

The continuity test on the distributor is as follows -

Tilt switch disconnected.
Voltage on Red wire at SwitchBox (SB) is 11+ volts on cranking. (was told it should read 9.5 + volts)
Voltage on White wire at SwitchBox (SB) is 11+ volts on cranking. (was told it should read 9.5 + volts)
Voltage on WHT/BLK wire at SwitchBox (SB) is 11+ volts on cranking. (was told it should read 9.5 + volts)
DVA voltage was not measured at BLK and BL as I do not have a DVA adapter. (was told it should read 2.5+ VDC)
* If voltage was lower than 9.5v, I should jump RED and WHT wires at the switch box. Voltage was above, so this was not performed.

----------------------------------------------------------------------

Continuity test to the distributor. (Distr. off the motor) as follows -

WHT/BLK to BLK reads 34 OHMs
BLK to body of Distr shows connectivity.
BL to BLK reads 34 OHMs

I'm not sure what spec should be.

With the distributor off, there are no visible signs of corrosion or shorts to the wires going in to the unit. Ground straps were also replaced as well as direct connection to ground on the distributor to negative of the battery.

So before I give up hope and turn this in to a winter project and also possibly purchasing another distributor (used or new), can someone possibly tell me if I've done all the tests correctly before I lose my mind and $$$ out of my wallet.

TIA
 
I think you have done the tests correctly, but the part (parts?) are still shot. The distributor on mine ohms out correctly but it still dead. The switch box requires a sophisticated Merc tester to check out correctly.

Sorry.

Jeff

PS: If you have a good block there (good compression readings) you could sell it on E-bay. Good ones are hard to find. The lower unit is valuable as well.
 
fastjeff said:
I think you have done the tests correctly, but the part (parts?) are still shot. The distributor on mine ohms out correctly but it still dead. The switch box requires a sophisticated Merc tester to check out correctly.

Sorry.

Jeff

PS: If you have a good block there (good compression readings) you could sell it on E-bay. Good ones are hard to find. The lower unit is valuable as well.
Click to expand...

Thanks @fastjeff. I understand I may still be SOL. The distributor will be the last part I buy and try for this engine before it becomes a parts engine and I start shopping for a good runner.

I do appreciate all of your feedback and help.
 
Back
Top