1978 Merc 90HP - All New Wiring - ISSUES

samm835

Chief Petty Officer
Joined
Dec 12, 2006
Messages
575
As you can read this is an older motor. The motor wires were starting to crumble and a majority of the needed replaced. This motor also had some handy dandy work from the prior owner, which he apprently didn't know jack about wiring. Any onto my issue. This is what has happened so far. I have replaced every internal wire on this motor, also starter soleniod, stator(wires were fried), so at this point I know every wires is new and is definitly in the right spot. I turn the motor over....and I think my ignition coil has gone out. I took it to my local shop and they said it could be the ignition coil or the switch box. Good lord Mercury loves that switch box(452.00). The ignition coil is around 125.00 if i remember correctly. My main question is since I have replaced and corrected all the wiring....could I be toasting everything that is old and not replaced? I mean I want a good reliable motor, but damn that switch box is freakin crazy expensive. Anyone want to give me a pointer on finding out if its the switch box or ignition coil? I do have a manual, I am not a mechanic...but point me in a good direction and I can do it. Can a switch box just go out? How common would it be for that to go out? I guess same question for the ignition coil?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,829
Re: 1978 Merc 90HP - All New Wiring - ISSUES

There is a simple test for the switchbox and coil, on those distributor ignitions. it is avail here in this forum or on the CDIElectronics.com website. It assumes the coil is good, because most are. There are resistance tests for the coil as well.

BTW aftermarket coils and switchboxes are avail for that motor. They are superior and cheaper than OEM.
 

samm835

Chief Petty Officer
Joined
Dec 12, 2006
Messages
575
Re: 1978 Merc 90HP - All New Wiring - ISSUES

Chris thanks for your help, I am looking up the details to find out if these are actually bad. I have looked online for these parts....and I can't find them that seem to be "good prices". Granted they are better than the marina price...but still not great. Thanks a great deal for the site!

EDIT: I went to the site here and there and maybe I am just looking in the wrong places, but I wasn't able to find any test procedures. Thanks.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,829
Re: 1978 Merc 90HP - All New Wiring - ISSUES

The CDIelectronics.com web site makes the tests easy to find.
 
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