Wiring Help - Merc 500 Thunderbolt 50hp

[Blake013]

Hi everyone, I have two random wires that are not connected on my engine. A black wire on the port side on the bottom terminal, and a blue wire on the starboard side again on the bottom terminal. I have no idea if the wires are original or changed, the blue wire does look newer then the others. I have tried looking at wiring diagrams online but i could not work it out.

On the Port side, there is a second wire on the terminal that looks like it is going to the distributor.

On the Starboard side, there is a second grey(white?) wire on the same bottom terminal that feeds into the main harness to the 8pin plug on the side of the motor.

The engine is from a boat i am restoring and i was told that it was running before the timing belt snapped. I am awaiting a new belt, starter motor and ignition switch so have not yet had a chance to (attempt to!) start it.

Photos attached.

Thank you for reading and any assistance, it is appreciated.

Black Wire - Port Side





Blue Wire - Starboard Side

 

[merc850]

I think you need a proper wiring diagram use the serial Nr. to find it, then, you should clean all the wires and terminals as they are badly corroded.
The carbs should be cleaned and float settings done and a compression test as well, a manual is your best investment.

 

[Blake013]

I finally found the serial number on the side of the engine thanks to another thread on here which tells me it is a 1968 engine. Using this site (https://www.maxrules.com/mercwireindex.html) i then have been looking at "Merc 500 Thunderbolt..........Internal & External Wiring Diagram" but this is the same that i was looking at before and where i got confused as i didn't think it was the same engine.

Yes, i have done one side and fixed several frayed wires and heat shrinked the ends and will do them all to give the old girl the best chance to run just not sure about these 2 wires...!

Compression is okay, the carbs i'll bath & clean and assuming it fires i'll then do a lot for the gaskets.

Good shout on the manual. Will find and order.

Thank you.

 

[racerone]

Serial # of this motor is ??----Take a look at wiring inside control box as well.

 

[Blake013]

Serial # of this motor is ??----Take a look at wiring inside control box as well.

2305830 is the serial number.

I have removed the cover now to clean it and the wires up and trace them back.

 

[Blake013]

I did some more research on this....

Following the link from here, which is the engine i thought i had: https://www.marineengine.com/parts/mercury-outboard-parts/500/2305101-thru-2858813#

Shows this part:
https://www.marineengine.com/newparts/part_details.php?pnum=MER333-3213A+3

...which is different rom mine.

Yet my switch box seems to match the switch box listed for this one:
https://www.marineengine.com/parts/...-starter-solenoid-rectifier-and-wiring-harnes

Actual item: https://www.marineengine.com/newparts/part_details.php?pnum=MER332-2986A27

So not sure if i have a engine which has been modified or if the cowlings are wrong as they say 500 and 50hp.

Would Mercury be able to confirm the model if i supply them the serial?

 

[merc850]

This should be the wiring diagram for your motor it seems to be a 1968 model.

 

[Blake013]

This should be the wiring diagram for your motor it seems to be a 1968 model.

View attachment 377404

Thank you!

 

[merc850]

Thank you!

If you are doing any work to the distributor don't try to pull off the rotor it's molded on to the shaft just clean the tip with a light sanding.