Ammeter For 1972 Johnson 65hp

jay_merrill

Vice Admiral
Joined
Dec 5, 2007
Messages
5,653
I picked up a NOS Aqua Meter ammeter for 20 bucks the other day, and may want to use it. I already have a hole of the correct size in my dash, which is currently filled with a trim indicator that is of no use to me. Since my motor doesn't have tilt/trim, I may as well use the hole for something useful.

So, the question is, how do I hook it up to my motor. I know that I need a 10 guage run of wire between the "BAT" post on the guage and the common lead on my battery switch, but what do I hook the other post to?

I also know that the other post on the meter goes to "the alternator," but I am not sure how to translate that into the wiring layout for my motor. I'm thinking that it should be connected to the #5 post on the engine's terminal block (see diagram, below), which receives 12VDC from the rectifier.


1972J65hpWiringSchematic.jpg



I've already seen some of the threads that talk about the value of an ammeter v. a voltmeter (already have one of those), but none of them seem to provide information on how to wire the ammeter. Any thoughts by the members will be appreciated!


PS: If you can't read the wiring diagram because of the image size, right click, save picture as, and then view with Windows Picture & Fax Viewer, which has a zoom function.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Ammeter For 1972 Johnson 65hp

I don't know what range the ammeter is, but if you run it in the main battery circuit you are going to be pulling starter motor current through it... Good bye meter.. :eek:

The best place to run them is in the wire between the output of the rectifier and the main lead on the starter solenoid from the battery... That will only give you a read out of the current the alternator is producing... But there isn't am easier way of doing it....

Chris..........
 

jay_merrill

Vice Admiral
Joined
Dec 5, 2007
Messages
5,653
Re: Ammeter For 1972 Johnson 65hp

The meter reads plus or minus 30 amps.

There is a wiring diagram with it that clearly shows the "BAT" terminal on the meter going to the positive lead on "the battery." Since I have two batteries, which are connected to an A/AB/B type battery switch, I would think that I would have to run the "BAT" circuit to the common positive on the switch.

See the diagram below - the ammeter wiring is on the right side.


AquaMeterWiring.jpg



From the diagram, it looks like the other post is connected to both "the alternator" and the switched side of the ignition switch. The #5 post on the terminal block in the engine, is a point between the output side of the rectifier and the starter solenoid post, and I am thinking that the other wire could go to the "purple wire terminal" on the ignition switch. Alternatively, it could go to the same circuit (purple wire) that runs to the voltmeter.
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Ammeter For 1972 Johnson 65hp

.... The #5 post on the terminal block in the engine, is a point between the output side of the rectifier and the starter solenoid post, and I am thinking that the other wire could go to the "purple wire terminal" on the ignition switch. ...

Hell-lo, That's what I suggested...

Can't run it the same as a voltmeter.. Voltmeter measures Voltage across a device... Ammeter measures current through a device....

Chris.........
 

Brad750

Cadet
Joined
Jul 8, 2011
Messages
6
Re: Ammeter For 1972 Johnson 65hp

I picked up a NOS Aqua Meter ammeter for 20 bucks the other day, and may want to use it. I already have a hole of the correct size in my dash, which is currently filled with a trim indicator that is of no use to me. Since my motor doesn't have tilt/trim, I may as well use the hole for something useful.

So, the question is, how do I hook it up to my motor. I know that I need a 10 guage run of wire between the "BAT" post on the guage and the common lead on my battery switch, but what do I hook the other post to?

I also know that the other post on the meter goes to "the alternator," but I am not sure how to translate that into the wiring layout for my motor. I'm thinking that it should be connected to the #5 post on the engine's terminal block (see diagram, below), which receives 12VDC from the rectifier.


1972J65hpWiringSchematic.jpg



I've already seen some of the threads that talk about the value of an ammeter v. a voltmeter (already have one of those), but none of them seem to provide information on how to wire the ammeter. Any thoughts by the members will be appreciated!


PS: If you can't read the wiring diagram because of the image size, right click, save picture as, and then view with Windows Picture & Fax Viewer, which has a zoom function.

Is there any way you could email me a higher quality copy of this photo? Or tell me where I can find one. I have a 72 johnson that someone has been tinkering with the wiring and from what I can see in this photo there is a LOT wrong. Thanks

yellowgix750@hotmail.com
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,758
Re: Ammeter For 1972 Johnson 65hp

I don't know off hand what the alternator output is for a 1972 Johnson but it is very likely 10 amps or less. That makes the ammeter virtually useless on that motor since the needle will ever barely move. Just because you have the instrument does not mean it has any real value other than plugging a hole.
 

seahorse5

Rear Admiral
Joined
Jan 24, 2002
Messages
4,698
Re: Ammeter For 1972 Johnson 65hp

Forget using the ammeter, that causes a voltage drop plus you will have many feet of heavy wire that is always "hot" and not fused. It could cause one heck of a fire should something happen. OMC got rid of ammeters for those same reasons. Put a voltmeter in the 2" gauge hole, its easier to hook up and tells you more.
 
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