1975 Mercury 500EL Lightning Energizer wiring…

ryanp1227

Petty Officer 3rd Class
Joined
Apr 17, 2022
Messages
78
Ive checked the diagrams. I seem to have this right, but need an answer from someone more knowledgable than me. From the Mercontrol, I have Red, Black, Yellow, White, Salmon, Brown, Grey. Engine side, same colors. My question is about the white wire, specifically.

CDI says it is not used on the engine side. The other two relavent diagrams from maxrules and the service manual do not show a white wire on the engine side.

The way the control is set up, white seems to act as 12v for both the choke button and the tach lead. It shows the white wire present on the control side of the harness, marked as “F” and in the center pin position on the connector. However, in all the diagrams, thats it for the white wire. Just terminates in the harness connector.

It would seem that the matching white lead on the engine side would go to a 12v source, right? Not just for the tach, which there is also a brown lead for, but also for the choke? Should that be to the rectifier terminal with the red lead connected? Or should it be straight to the solenoid with the main red power wire (doesnt seem likely as then it would not be a switched power source).

Long post for a short answer, but Id rather lay out my full process now instead of getting the third degree later. I checked forums as best I could. Lots of wire related info, but mostly in regards to the tach.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,854
The white wire is ign power. If it unused on the later ADI ignitions, and maybe unused in your motor as well. Merc likely wanted the boat harnesses to be universal, so you could easily replace the motor with a larger or newer one, w/o changing the boat harness or control,

It is a guess, but a reasonable one, IMO.
 

merc850

Commander
Joined
Jul 7, 2010
Messages
2,046
That motor uses a self energizing "magneto" so the white wire just powers the choke and tach as shown in the wiring diagram - it doesn't need 12v to operate. And as Chris said the control harness can be used for many HPs
1975-500small.jpg
this is the wiring for 8500/1250/1400 etc the white engine harness wire activates the ignition
75-850wiringsmall.jpg
 

ryanp1227

Petty Officer 3rd Class
Joined
Apr 17, 2022
Messages
78
Ok good so that makes sense, and what my guess was but I just needed clarification. The white on the engine side, even tho it is omitted on my diagram, goes to 12v…which in my case will be the rectifier Red wire. Thank you
 
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