Replacing Mercury switch boxes in pairs

[boatbonanza]

Hello,
This is my first post but I have already learned tons from these forums in the last few days. Bought a 1984 90hp Merc. that has been diagnosed as needing the switch boxes replaced. I understand the idea of replacing both at once so a bad one does not damage a good one, my question is if I found a good used one locally cheap from a 3 cyl. then picked up a good used one from Ebay both with the same 332-7778A1 part number would that be acceptable. Or for some reason do they need to be matched or installed in a particular orientation? Just curious if someone has some insight.
Thanks for your time.

 

[Faztbullet]

Re: Replacing Mercury switch boxes in pairs

The A1 is a old part number as the newest is A12, and how do you know packs are good?? Have they been tested??? Below is testing from CDI....
Disconnect white/black wire and check the bias circuit (white/black terminals) resistance to engine ground. Readings should be approximately 15,000W for standard packs....

 

[boatbonanza]

Re: Replacing Mercury switch boxes in pairs

I am assuming that the local one is good because it was running fine when the lower unit was damaged. And as far as the ones on Ebay a couple of them come from used parts dealers that guarantee them to work and have been tested. Anyway I tested resistance from the disconnected bias circuit (white /black wire) between the boxes from each box to the ground plate that the boxes mount to. I got 14 ohms on one and 16 ohms on the other. So if I did everything correct that means junk switch boxes. I just want to see everything else work well before dumping a pile of cash into a pretty outdated engine.

I had read on a web site that was trying to sell new switch boxes not to use used ones because there can be timing issues and resulting engine damage. I don't want to try and save a couple hundred dollars and trash the whole engine. Is this a likely possibility? Or a very slim remote possability? If both boxes test good are you safe to use them? Thanks again.