Silly question about '78 Mercury ignition 90hp, L6

[Nohfire53]

I have posted before, I have no spark to any plugs.

I just did a test that was posted on this forum where I jumped the Brown and White wires on the switchbox then ground it, I got no spark.

The red is hot at 12.??? with the ignition off.

The white is hot with the ignition on 12.????

I ground the box bypassing the distributer and got no sparking from the ground. This shoul mean that the switchbox is bad, correct?

Question 1: Would hooking up battery cables backwards :facepalm:fry the switchbox, is that common?

Question 2: Any websites I can get a Cheap used or OEM switchbox that old?

P.S. This Forum rocks, thanks to all who have helped me the last few days...

 

[Maxz695]

Re: Silly question about '78 Mercury ignition 90hp, L6

use swtcboxes can be found on eBay and other sites posted on threads like johns old parts or something . Yes hooking you battery up wrong can burn out the rectifier in a second and even burn out the switchbox as well

 

[narvlebenoit]

Re: Silly question about '78 Mercury ignition 90hp, L6

the only thing I have a 84 modle and it has two switchboxes Iwas told when you change one you should change bougth of them I put to new ones on my motor last year they were CDI and they coast 132.00 dollars a peace but check eBay they usally have some used ones on their cheap good luck.

 

[Chris1956]

Re: Silly question about '78 Mercury ignition 90hp, L6

Usually the switchboxes survive battery cable switching.

OK, Red wire on switchbox s/b always hot. White wire hot, when ign switch in run or start position. Pull heavy spark plug cable out of coil, unscrew it from distributor cap center and reinstall it into coil. Disconnect electric. Disconnect the 3 distributor wires. Jumper brown and white posts on switchbox (where you removed dissy wires) together. Put jumper on black switchbox post. Reconnect battery power. Now, Ign switch in run positon, hold coil wire close to block or other ground. Touch jumper on black switchbox post to ground and observe spark. If no spark, wiring is bad, switchbox i bad or coil is bad.

 

[Nohfire53]

Re: Silly question about '78 Mercury ignition 90hp, L6

So how do I determine whether or not it is the switchbox that is fried or the rectifier?

 

[Chris1956]

Re: Silly question about '78 Mercury ignition 90hp, L6

The rectifier on that model has no effect on the ignition system. You may ignore it. There is a rectifier test on the sticky notes, I believe.

 

[Nohfire53]

Re: Silly question about '78 Mercury ignition 90hp, L6

Thank you so much Chris, that is what I thought, I was awaiting verification on my hunch.

 

[Nohfire53]

Re: Silly question about '78 Mercury ignition 90hp, L6

Got the new switchbox yesterday, 2986 a8, It's installed and the motor runs great!

Thanks for all you help everyone