How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Dominick Your Own Question
Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
Type Your Boat Question Here...
Dominick is online now
A new question is answered every 9 seconds

how do i test the coil packs and brain box on a 25 hp mercury

This answer was rated:

how do i test the coil packs and brain box on a 25 hp mercury outboard engine

Thank You for Your QuestionCustomer


There are tests for the ignition charge coils (Stator Coils), the Trigger coils, and ignition coils...but there is no tests for the Control module...How this works is, test the components that you can, and if they test good, change the Control module....


If you have no spark at all, it is not the ignition coils - Odds of both coils going out at the time are "NOT"...


Give me your Model and Serial number of the engine and I will look the tests up for you...


Dominick and other Boat Specialists are ready to help you
Customer: replied 8 years ago.
dont know the model but the only serial # XXXXX can find is 0b224421


The serial Number came up as a Belgium Engine (Weird, Unless Your In Belgium !!!)


The Model # XXXXX(NNN) NNN-NNNN- Ser# XXXXX - 25 HP Twin Cylinder Mercury / Mariner..


The parts below are -


All Tests are using a DVA (Direct Voltage Adapter) Type Meter With Sparkplugs Removed and Coils Attached to a Spark Board (Use The Sparkplugs Grounded to Block)


Stator/Charge Coil - #2 - 20V+ High Speed Coil / 180V+ Low Speed Coil


Sensor Coil - #7 - Same Test as Above - 5v Pulsing


Ignition Coils # XXXXX - 180V+ Pulsing From Control Module


Power Pack / Ignition Control Module - # XXXXX = PN#339-7452A3 No Longer Available From Mercury but is Available From CDI Electronics PN#(NNN) NNN-NNNN 3 For = $158.00







Customer: replied 8 years ago.
is there an ohm reading i can do on it and if so which wires read what

Ohm reading on the Ignition Computer??? No....


Ohm readings on Coils is a haphazard way of testing, if it test bad it may not be, This is because the resistance will vary with temperature and age. I could not find the values for the coils, and I would not recommend this method of testing...We do see these resistance measurement for other models, but once again we don't recommend this type of testing....Either it will produce the required voltage or it won't, much better...The DVA volt meter is available from SIERRA Marine Supply and Cost about $65.00, less than a hour labor at the shop...

Customer: replied 8 years ago.

Your very welcome, If you get a moment to FeedBack, I would apreciate it....


Thanks Again,