2003 Mercury 15 HP 4-stroke won't fire

[Buckeye55]

Hi all.

I am a leader with our local Sea Scout group. We received a 12 foot dinghy with a Mercury 15 HP four stroke as a donation. The boat and motor had been left in the water for about six months. Needless to say, they needed a little TLC before we could attempt to start the motor. New battery, battery cables, plugs, electrical contacts cleaned, new fuel, etc.

The motor is electric start and turns over with authority. Kill switch is in the correct position.

Did some old school checks: starter fluid in the top cylinder, with spark plug removed but connected checked for spark. No joy.

Any recommendations as to the most effective way to troubleshoot for the lack of spark would be appreciated.

 

[Star]

I am not sure but I think some of these motors had safety lanyards on them. You will need a mercury manual with ohm readings on the ignition components. don't get the after market version!!! there are also many wire clip connection that can be loose also.

 

[Buckeye55]

More detail:

Apparently the previous owner either hooked the battery up backward or tried to jump it and put the cables on in reverse. The ignition circuit was fried (Rectifier and CDI). The coils (lighting and charging) were exposed to high heat. The Pulser was open. All have been replaced. The primary coil is showing nominal resistance and has not been replaced.

It appears that I am still not getting voltage to the primary coil. All electrical connections have been cleaned.

The kill switch is in the correct position. However, I can not find the wiring diagram for the ignition switch, kill switch and the associated harness.

 

[Star]

My coil primary checked ok but had some problem that it would shut down one cylinder when hot. I don't think he could blown all that stuff unless he bypassed the fuse!!!

 

[rwgrassl@verizon.net]

We have almost exactly the same no spark issue with a 15hp 4 stroke 2002 merc. Left in the water too long. All corroded up. Looks as if someone may have put the battery on backwards. Starter spins the engine just fine. Fuse is good. An analysis by a Marine dealer said the electronics were cooked. Wants $400 to work on it. We also found later that the coil for the timing was burned out (Ohms check, open). We have replaced all of the electronics (some ebay used parts). No joy yet. We think the igition key switch is the (last?) culprit. We see no voltage to the ECM with the key switch on. $55 for a brand new, not returnable potted switch. Has 6 wires, but no info on what it has inside. We have to cut/solder the wires on the new switch to match the wiring length & plug ends on the old one. I'll repost if we have success! Ron... sea scout ship 618.