1975 Johnson 115 Rectifier Question

[scottzfx]

So based on all the help I've gotten so far. I decided to add a tach so I can check RPMs at WOT and just for the coolness factor. Undid the rats nest of wiring the PO did and made a nice switch panel and wired the tach. The gray wire still had the cover on it. Wired everything up, turned ignition, the tach went to zero. Then turned the motor over but nothing from the tach, still at zero. Checked wiring, all good. Did voltage check on battery (hadn't done this before). Voltage with motor off was 12.8, voltage with motor running, 12.6. Ah ha, not charging. PO had wing nut on negative lead, which I replaced after some previous reading. Stator "looks" good, no goo or anything leaking out. I'm going to change the rectifier and see if it works. Now, here is my question (finally):

Looking at http://www.iboats.com/Johnson_Regul...9398597--**********.714465346--view_id.271366, they say its a 12 amp system. Found the actual part number from engine diagram and did google search, all the other sites say 6 amp. Which is it? Will it screw anything up if I put a 12 amp on a 6 amp? (I'm assuming YES!) I'll defer to the vast pool of knowledge in these groups. Thanks!

 

[emdsapmgr]

Re: 1975 Johnson 115 Rectifier Question

Both the 115 and 135 that year used a 6 amp stator, according to the OMC parts list.

 

[Randyg123]

Re: 1975 Johnson 115 Rectifier Question

Everything I've seen says 6-amp but then I have also been confused because I have seen literature that says 12-amp if Tilt-n-Trim installed. Not sure if that is in error. OEM manual for my 1975 135HP says 6-amp. i would assume yours to be the same.

 

[Joe Reeves]

Re: 1975 Johnson 115 Rectifier Question

The 1975 115hp Johnson has a 6 amp charging stator. There is only one rectifier for that engine which can be tested as follows below.

You ask "Will it screw anything up if I put a 12 amp on a 6 amp?" I have no idea what that means.

(Small Rectifier Test)
(J. Reeves)

Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.

Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.

Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.

Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.