I found a similar post that ended without a solution, so I copy and pasted the intitial post to save time in typing:
I have a 2003 merc 4.3L with thunderbolt V ignition
-I have 12 V at the + on the coil, it is within .3v of battery voltage. So very little wiring resistance
-I have 12 V at the red and white wire coming from the TB-V.
-I have disconnected the gray tac wire from the tach and verified the grey coil wire is not shorted
-I have disconnected both wires from the shift Int switch
-I have a gap light at the coil, no spark.
-If I take the green/white wire from the TB-V and tap it to a ground I get spark. This points to a bad ignition sensor.
--Installed new cap, button, and Quicksilver (Mercruiser) Distributor sensor still no spark.
I then took a steel ruler and passed it though the sensor and old one (should go from 0v to 5v) but they didn’t. There is no voltage coming from the distributor grn/wht wire or any 0-5v pulse that the flow charts mention.
Can that mean another faulty sensor?? Even though I opted for the more expensive Quicksilver one??
I found another test in order to verify the module is working properly:
voltmeter red lead to wht/red lead coming from ignition module black meter lead to good ground, key on should see 12 (+) volts, with meter still attached hold the wht/grn wire from module to good ground and see if voltage drops momentarily then returns to 12 (+) volts - this will tell you the module is good and you need to replace the ignition sensor in the distributor
This test passed, it also produced a spark from the coil....
I also hooked up a wire to the - terminal of the coil with grey wire from the module still attached. Then struck it to ground. That produced a good spark from the coil? This indicates nothing is shorting out the signal side (-) of the coil. I'm out of ideas and can't find what the culpret can be. I've foloowed the flowchart for a TB-V to a tee and it still points to the dist sensor being faulty...What else can it be? I've got 2 after market sensors coming...Cheap $32.00 ...Last ditch effort before throwing an AC Delco Est or Pertronix in it! This is wearing me out! Have had this boat for about 12 years, always stored indoors and first electrical issue I've ever had with it.
I have a 2003 merc 4.3L with thunderbolt V ignition
-I have 12 V at the + on the coil, it is within .3v of battery voltage. So very little wiring resistance
-I have 12 V at the red and white wire coming from the TB-V.
-I have disconnected the gray tac wire from the tach and verified the grey coil wire is not shorted
-I have disconnected both wires from the shift Int switch
-I have a gap light at the coil, no spark.
-If I take the green/white wire from the TB-V and tap it to a ground I get spark. This points to a bad ignition sensor.
--Installed new cap, button, and Quicksilver (Mercruiser) Distributor sensor still no spark.
I then took a steel ruler and passed it though the sensor and old one (should go from 0v to 5v) but they didn’t. There is no voltage coming from the distributor grn/wht wire or any 0-5v pulse that the flow charts mention.
Can that mean another faulty sensor?? Even though I opted for the more expensive Quicksilver one??
I found another test in order to verify the module is working properly:
voltmeter red lead to wht/red lead coming from ignition module black meter lead to good ground, key on should see 12 (+) volts, with meter still attached hold the wht/grn wire from module to good ground and see if voltage drops momentarily then returns to 12 (+) volts - this will tell you the module is good and you need to replace the ignition sensor in the distributor
This test passed, it also produced a spark from the coil....
I also hooked up a wire to the - terminal of the coil with grey wire from the module still attached. Then struck it to ground. That produced a good spark from the coil? This indicates nothing is shorting out the signal side (-) of the coil. I'm out of ideas and can't find what the culpret can be. I've foloowed the flowchart for a TB-V to a tee and it still points to the dist sensor being faulty...What else can it be? I've got 2 after market sensors coming...Cheap $32.00 ...Last ditch effort before throwing an AC Delco Est or Pertronix in it! This is wearing me out! Have had this boat for about 12 years, always stored indoors and first electrical issue I've ever had with it.