1975 Mercury 500 50 hp

[DeweyDeb]

re-wired my motor because it was really corroded. I followed a diagram that matches up to mine, but can not upload to you. But when I turn the key I get nothing? So what I did next is if I take a wire straight from the Battery and add it on to the red wire going to the receptacle, it will crank but not start? I get no spark from the Plugs either so I have some problems and any help on where to start would be really great. I know how to use a meter

 

[GA_Boater]

Welcome aboard, Dewey.

Do you have a kill switch lanyard? That will kill sparks. Are you in neutral? That will inhibit cranking.

 

[DeweyDeb]

I have move the throttle back and forth to see if the neutral was off but that did not work, as for a kill switch I took the control box apart and it did not look there was on there? Is that where I would find it?

 

[Chris1956]

The Maxrules web site should have a wiring diagram for your motor. Does it have a distributor? Also the CDIElectronics web site will have a troubleshooting guide for your ignition.

 

[DeweyDeb]

Maxrules does not go back to 1975, and CDIElectronics is a training company

 

[procraftguy]

Do you have a white wire in the box?if so that is like ur kill switch it enables spark at the switch box confirm with meter u have power with key on at switch box on white wire then on red if not somthing came lose

 

[DeweyDeb]

here is the wiring. I do not have a white wire on harness but I do on switch box, should I have power on red, and white there?

 

[Chris1956]

Here is your wiring diagram from maxrules.

http://www.maxrules.com/oldmercs/Wiring/1966ona/26A.jpg

CDIElectronics sells many ignition and voltage regulators for outboards. They are kind enough to provide a detailed troubleshooting procedure for outboards.

If I am reading the wiring diaghram properly, no voltage is sent to the switchbox, to run the ignition. The switchbox is ungrounded when spark is desired,

 

[DeweyDeb]

Thanks Chris, But can you tell me what color wire on that diagram feeds power to the control box?

 

[Chris1956]

The wiring diagram indicates that no power is fed from the battery to the switchbox. It is likely the distributor has some sort of magneto, which charges the switchbox. The CDIElectronics troubleshooting guide should describe it.

 

[robbiej_82]

Hey,

Was Reading This and it Sounded Like my Issue to a T. Not sure if you've solved your problem. I Recently also rewired my 1975 Merc 500 Thunderbolt and I had the same problem. Even used booster cables from battery to starter solenoid to turn over but no spark.

Solution: After digging around I realized I had forgotten to ground the Starter Solenoid. There is a Positive and Negative on the Ignition Coil, The Positive Wire
From The ignition Coil goes to the bottom terminal on the switch box, the negative wire from the ignition coil goes to the negative terminal on the starter solenoid and then the starter solenoid grounds by bolting it to the coil bracket. If This is NOT grounded exactly what you described happens. No Crank from Key and No Spark if jumping the starter.

Hope This Helps.

 

[robbiej_82]

Also There is NO direct power from battery to switchbox, Direct Voltage From Battery to Starter Solenoid Only! Your Ignition Driver (Driven by Timing Belt) provides the voltage to the switchbox it has 3 Wires going to the
switchbox. You Should have around 100VAC on the Top Terminal and around 50VAC on the 2 below it. The Stator On the Flywheel Has 2 Wires On it That Provide AC Voltage to the Rectifier which changes the Voltage to DC and Charges the Battery. That Stator and Rectifier ONLY charges the battery.