1970 Merc 115 no spark

[gator1959]

hi all,my 115 has run perfectly this season,the water stream was a tad weak so,I put in a new impeller last night, as the hot weather season has arrived, ,and during assembly,we accidently hooked up the battery backwards for a few seconds,while bumping the flywheel for the driveshaft to mesh with the powerhead/crankshaft,......all that went well,but when we tried to start it today,she turned over normally then wouldn't start,a few quick checks and we found no spark at the plugs,we have 12 volts at the switch constantly with key off(red wire),and 12 volts with the key on on the white wire. ,on the distributor side we only have a faint trace of power on the bottom wire which also has the points condenser hooked to it,Is this something simple? thanks.

 

[gator1959]

Re: 1970 Merc 115 no spark

just to make a few things clear,this is a fresh (2 year old powerhead rebuild) w/130+ psi on all 6,carbs rebuilt and tuned perfectly,and fuel pumps rebuilt this season,and now a fresh water pump rebuild and new prop.it has been on the water 10 times this year already,and performs flawlessly,until today's no start.It is definitely an electrical issue,just not sure which component got fried.

 

[longjohn119]

Re: 1970 Merc 115 no spark

I'm not an outboard mechanic but I am an ISCET certified electronics technician (amongst other things)

Unless Mercury included some reverse voltage protection into the switchbox, chances are you fried that puppy. Reversing the voltage to an electronics device like that is probably one of the worst things you can do and is the cause of many failures. Since like most manufacturers Mercury 'blackboxes' their electronics and gives us no clue whatsoever to what is in there, there is no way of knowing if any reverse voltage protection was included. This is also a major reason most electronic parts for autos, cars and other devices are non-refundable because they got tired of having to warranty devices that failed not through any manufacturing fault but because it was hooked up in reverse

Probably not what you wanted to hear but please do not shoot the messenger (Me)

 

[Moody Blue]

Re: 1970 Merc 115 no spark

Sorry for your luck but chances are you cooked the switchbox. That is the one most important things you must prevent - reverse battery connection. At the very least you blew the rectifier but most likely the switchbox is gone.

Search the forum here for a procedure to test the switchbox. It is simple and easy to follow and will clearly determine if yours is good or bad.

Good luck.