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1977 Mercury 150 hp Switch Box issues

S

scoutfamily

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"I have a 1977 merc 1500. I h

"I have a 1977 merc 1500. I have replaced the switchbox. I install a new one the boat runs for a couple of weekends and then I go out to the start the boat and there is no spark, test the box and it is bad. I am at my wits end. Does anyone know anything about these engines and what would cause the switchbox to go out so many times????? All I want is to fish sometime this year. :)"
 
A bad stator will fry a switch

A bad stator will fry a switchbox - have it tested before you toast another ignition component...
 
"IF it is causing the switchbo

"IF it is causing the switchbox to fry it's because it's putting out wild voltages, so simple resistance tests (to check the state of the windings) are of no value.

The stator produces AC and requires either a DVA Meter or a DVA (direct voltage something) Adapter (for a standard volt meter - which is then set to at least 400 Volts DC - doesn't sound "logical" but that's the way it works) and the sustained peak voltage is measured.

I don't have the exact specs for your motor but usually peak voltage should be in the 300-350 Volts (DC according the the meter) range @ 3000 rpms from both the high and low speed windings.

Below that range would result in weak/no spark, above that range (significantly) could cause a few of the internal switchbox components to fry (blocking diodes, SCR, capacitors etc).

So after all my babbling, unless you have a DVA meter (or adapter) or know someone who does, you will need to get the motor into a shop to have it tested - but the motor must be assembled and running, you can't remove the stator and take it in by itself for voltage tests.

In addition to any Marine place, most motorcycle/atv shops can test it as well since their ignition systems are almost identical to that found on outboards..."
 
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