1972 merc. 800 no spark?

[oldglastron]

Hi,
I am helping a friend repair his boat. We have a 1972 800 (80hp) 4 cylinder. He has a book but it is not OE. The wiring diagram colors do not match the switch box. (book thunderbolt III ignition) I currently have 12v to the red wire also at the rectifier. The mercury switch is gone. The distributor looks new we rewired the control box. My question is, what colors and in what order do the wire colors go. maybe a wiring diagram or switch box test procedure would be handy. I did test from spark at the coil tower. This thing was in pieces, I have done several of these and never had a issue before. Thanks. (oh yeah the colors I have are green black red and white)

 

[Chris1956]

Re: 1972 merc. 800 no spark?

You have the old wiring colors. Is the engine harness in good shape? Normally thay are real bad unless they were replaced. Red is battery power and is always hot to the switchbox and rectifier. Green is switchbox to coil. Yellow is starter solenoid (and stator wires to rectifier). Distributor will have white, brown and black wires to the switchbox. Under the red wire on the switchbox is a white wire. This is supposed to have power when ign key is on. Brown on switchbox (non distributor wire) is tach sender wire.

There is a test for that ign system on the CDIElectronics web site.

 

[oldglastron]

Re: 1972 merc. 800 no spark?

Thankyou Chris I will test it all today the boat has been in storage for a month. time to finish the project.

 

[oldglastron]

Re: 1972 merc. 800 no spark?

ok, the engine runs great however it does not shut down... what wire on the control box needs to ground when the switch is turned off. I am guessing one wire grounds the coil to shut it down. It looks like maybe the white wire on the control box? However that wire is hot with the key on. Let me know what you think.
Thanks.

 

[1960 Starflite]

Re: 1972 merc. 800 no spark?

I learning on a 850 type III ign. I believe there is power on the red wire all the time. The white wire has power from the run position on the key switch. To shut the engine down with the key in the off position there should be NO power to the white wire. You don't kill the engine by grounding like the magnito systems, which will run without any external power supply.

 

[Chris1956]

Re: 1972 merc. 800 no spark?

Starflight is right......