77 merc 700 no spark

[kylehartig]

i have a 77 merc 700 and i have spark tested all the cylanders and number 1 cylander would not spark so i replaced the coil wire and coil but still no spark this engine has a ignition coil for each cylander and one switchbox. i think because the other two cylanders work it cant be the switrch box so the only other thing would be the trigger maybe somehow it shorted or just plain broke the circuit for cylander one. i really dont know but the trigger and switchbox are the only components i could see being the problem.

any ideas would be a life saver i am low on cash and cant pay for a 200dollar inspection and be told after words its to much work to do on a 30year old engine.
thanks in advance

 

[tashasdaddy]

Re: 77 merc 700 no spark

you may find something here to give you some insight. there are quiet a few pages go thru them and find your engine. scroll down to mercury troubleshooting.

http://www.boatpartstore.com/tips.asp

 

[ricksrster]

Re: 77 merc 700 no spark

Since you are sure it is not the coil check resistance of trigger wires white/black to Brown and Purple to white. Each should have 800 - 1400 Ohms. If you have a DVA multimeter you can check the voltage. White/Black to Brown and Purple to White. Each should be 4V+. If you don't get these results it is a bad trigger.
Keep the Green wire and the black connected to the coil. The DVA between the wires should be 150V+. If not you have a bad switch box.