How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifier?

Sometime back after getting tired of paying $30+ for every Mercury 3 post rectifier that went bad, I checked this forum and got some great advice to stop using the Mercury 3 post rectifier and purchase an All Electronics FWB-352 rectifier 35 A 200 PIV Bridge Rectifier at $2.50 each. This new rectifier is about the same size, but has 4 pins with none grounded to the base. I used an old 3 pin rectifier base as a mounting plate for this new one.

By the way, I am putting this on a 1984 75hp 4 cylinder 2 stroke, but Mercury used the old 3 post on a number of models (maybe all?) in that timeframe.

Question:
How to wire it up?
(the diodes are not grounded to the base like the old 3 post Mercury rectifier.)

Thanks in advance for any suggestions.
(I think one of the posts likely needs to be grounded but of course experimenting with electrical components is not my idea of fun, LOL's!)

Re: How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifie

Having looked at the All Electronics web site picture of the FWB- recitifers the wires should conect to the post as marked on the side of the recitifer as indacated for each post. Check out the web site for the picture and see if the one you have is marked as the picture shows. If the center mounting hole is of metel then that could be the grounding post for the unit. JMO
Oldman570

Re: How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifie

Yes all you need to do is attach a ground wire from the negative terminal (-) to ground and then the two terminals that have a sin wave (AC wave form depiction) will connect to your alternator output coils and the positive or (+) will be your normal positive to where ever your original positive terminal went. If all you have is a two output coil alternator, this will work. It you have three coils you can also buy a three-phase recitier bridge and make those connections the same too. Have great day...:happy:

Re: How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifie

Thanks much for the quick responses!

Mine is only marked as follows (looking at the pin side):
Northeast corner +
southeast corner AC
southwest corner "no markings"
northwest corner "no markings"

I am betting the corner opposite the + is the negative so I will ground that one and see what happens.

BTW, the base is not grounded which seems funny to me. Also to mount it, I just chipped off the black plastic from an old bad 3 Mercury rectifier, drilled and tapped a hole in the center and put a screw through the single center hole in the middle of the new 4 pin rectifier to fasten it. I came up with this after diddling around trying to figure out how to mount the new rectifier.

Thanks again!

Re: How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifie

Usually you are right that the diaginal corners are the positive and negative outs and the remaining two are the AC ins. You could actually find out with a DVM. Most DVMs (Digital Volt Ohm Meters) meters have a diode setting to show if a diode is good or bad. In a full wave bridge like you purchased, it is nothing more then four diodes connected in such a fashion that AC input will yeild DC output. Same as your three wire rectifier circuit for your outboard The fourth wire on that setup was/is the case ground. So it too is a four wire setup just in a different package. So just connect the negitive terminal to any good ground source and the AC terminals will be your inputs and the positive terminal will be your output terminal...just exactly like the original rectifier...



The DC in should read DC out...

Hope that clears it up somewhat... :joyous:

Re: How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifie

Much thanks, put the opposite diagonal from the + terminal to ground and it works great!

Thanks again!:thumb::thumb:

Re: How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifie

Can you post a pic of the completed unit please?

Re: How to wire up a substitute 4 post rectifier for standard 3 post Mercury rectifie

will try to do this and see if I can figure out how to post a photo.