Electrical question

[painter.724]

Greetings , Would someone be so kind as to tell me were to hook up an amp meter.It came with the fairing I have along with a cig. lighter. I figured that since they are there, I might as well make them functional.I would assume one wire would go to the neg. on the battery ,but do not no were to run the other. If even that is correct. Thanks

[Garnet]

It depends upon the year of the bike.

You may have to do some rewiring to make an ampmeter work correctly.

[Ken in Oklahoma]

Greetings , Would someone be so kind as to tell me were to hook up an amp meter.It came with the fairing I have along with a cig. lighter. I figured that since they are there, I might as well make them functional.I would assume one wire would go to the neg. on the battery ,but do not no were to run the other. If even that is correct. Thanks

Do you really mean ammeter, as opposed to voltmeter? An ammeter will only tell you if current is flowing into or out of the battery and by how much. From that you can infer whether your charging system is operating properly. Hooking up an ammeter is problematic because you want it to show if your battery is charging or discharging, but you don't dare allow the current demand of the starter motor flow through the circuit. That would peg the needle and almost certainly ruin the ammeter (if it isn't adequately fused).

Editing: Oh, and an ammeter needs heavier wires feeding it than a voltmeter. The upper limit of the current handling requirement would be something approaching 20 amps, based upon a 240 watt alternator being able to supply 20 amps of current at 12 volts. A 100 watt headlight would demand close to 8 amps. Add in running lights and/or a heated vest or handlebars and more current potentially could flow through the ammeter under certain conditions such as starting up the engine with those functions turned on.

A voltmeter, which is what some of our airheads come with, won't give you as much of an indication as to how much current is flowing to or from the battery, but it will give you information that an ammeter can't; such as whether your battery is fully charged (engine not running). You will still be able to infer the state of your charging system as well as an ammeter (in my opinion). And to hook up a voltmeter is wonderfully simple.


Ken

[painter.724]

Thanks Ken ,Once again I am corrected. I read a writing on the subject of voltmeter versus ammeter from a fellow in the BMWSPORTTOURING forum in which his opinion was that a ammeter is a better diagnostic tool than a volt meter. I claim total ignorance on the subject, Knowing very little about electricity in any application.Having read that I decided to hook mine up since it was already mounted in the fairing. My bike is a r60/6 with only stock electrical components.No add ons. I am guessing that at one point someone had it connected to their BMW.If it will not hurt anything I also wish to connect it. Would you please point me in the right direction Even if this requires more than a few wires , It would be a nice project for me Thanks Dave

[Ken in Oklahoma]

Thanks Ken ,Once again I am corrected. I read a writing on the subject of voltmeter versus ammeter from a fellow in the BMWSPORTTOURING forum in which his opinion was that a ammeter is a better diagnostic tool than a volt meter. I claim total ignorance on the subject, Knowing very little about electricity in any application.Having read that I decided to hook mine up since it was already mounted in the fairing. My bike is a r60/6 with only stock electrical components.No add ons. I am guessing that at one point someone had it connected to their BMW.If it will not hurt anything I also wish to connect it. Would you please point me in the right direction Even if this requires more than a few wires , It would be a nice project for me Thanks Dave

Well Dave, as I've indicated, I personally believe the voltmeter is the better diagnostic tool for evaluating the charging system. For example, when you turn the key on, and the lights are off, if the voltage reads low, say 10 volts or less, you know that your battery isn't fully charged (or isn't capable of supplying more than 10 volts). If it reads way lower you know the battery is suspect or for some reason has been drained. Then with the engine running at, say, 2,500 rpm and the voltage is above, say, 13 volts or above you know that your charging system is charging. You don't know how much in amps, but you know the charging system is capable of delivering what it takes to run the bike plus some.

If the voltage is way low you know that you have a problem with an insufficiently charged battery or a bad battery itself.

I'm hesitant to mention specific voltages because the way BMW connects the voltmeter you're not actually reading the voltage at the battery. Rather you're reading the voltage after a drop due to the resistance in the wiring between the battery positive terminal and the ignition switch in the headlight.

But I'm going to quit talking about the voltmeter because you've apparently read both sides of the argument and have decided on an ammeter.

Going on then, the cable from the battery positive post disappears into the top cover of your engine. There the cable terminates at the starter solenoid where it supplies the heavy current to the starter as well as the rest of the the bikes needs. There will be a red wire connected to the solenoid which disappears into the wiring harness and comes out as one of the two red wires connected to the starter relay socket. ( I'm pretty sure that's done the same way for the /6 bikes as the later /7 and up bikes.) The second red wire from the relay socket then goes into another wiring harness and comes out inside your headlight shell and connects to the ignition switch.

You would pull that red wire off the ignition switch and run it to one terminal of the ammeter. Then you would run a wire from the second terminal of the ammeter back to the ignition switch.

Now, except for the starter current you will be monitoring all the current going to and from the battery. This is good because the starter can draw all of the current it wants without it going through the ammeter. I don't know how the terminals are noted on the ammeter, if at all. Since you'll be using an aftermarket ammeter it will likely come with directions telling which terminal goes to the battery and which terminal goes to the load. If the ammeter should indicate backwards you simply reverse the two wires to the ammeter.

You will, of course, have to string wires from the ammeter location to the appropriate points inside the headlight shell, but you're already planning on doing that.

I would also take the precaution of putting a fuse inline with the ammeter to protect it from a sudden short or a miswire. Know that if the fuse blows your whole bike will then go dead. And if you later have some electrical problem one of the things you will be wondering about is whether that fuse is blown. I don't know what the maximum current draw will ever be under normal conditions, but that would be with the ignition on (but with the engine not running), the headlight on high beam, and the horn blowing. I'm guessing that a 25 amp fuse would do the job.

I need to put a caveat in here. I'm away from my airhead wiring diagrams and I might have missed something critical or said something that is just wrong. I've never considered what it would take to put an ammeter on a bike (or car), and I'm making this procedure up as I go. Hopefully, if I've blundered, those others reading this post will catch it and correct it.

Editing: You know, that red wire coming from the starter relay may not go directly to the ignition switch. And I don't think even a wiring diagram would show me if it did. The red wire may go to that terminal board in the back of the headlight shell and then be "distributed" to other places, including the ignition switch. If such is the case you would pull off the red wire (coming from the starter relay) and attach your ammeter at that point, with the other wire from your ammeter now going to the terminal where you pulled the wire off.

I sure wish I had a headlight shell handy that I could look at.

Ken

[Airbear]

Dave and Ken - according to my Haynes diagrams for the /6 models the red wire from the starter relay does indeed go to the terminal board first, and then to the ignition switch.

Dave, what year is your bike? If it is a 74, shoot me an email and I'll send a colour wiring map that you may find useful.

[ME 109]

A word of caution Dave, that cig lighter may well be a 'joint lighter' and should have nothing less than jumper cable size wiring...... and no fuse.
Can you imagine blowing a fuse trying to light a big joint? Man, that would make me blow a fuse.

Then again, it may just be a cig lighter.
If so, disregard everything I've said 'cause I don't really know much about wiring.

[Rob Frankham]

I'm sorry to have to say this but there is some poor information here. I will try to clarify.

The situation is complicated by the fact that early /6 machines are wired differently to their later relatives and because there is more than one type of Ammeter.

This is the situation for the old type ammeter that only has two wires (ignoring wiring to the illumination lamp)

For the '74 year machines, the positive pole of the battery only has one connection to it, this is the big wire to the starter solenoid. A red wire to a seperate ring terminal on the same connection at the rear of the solenoid distributes current too and from the rest of the bike. To fit an ammeter to this type of bike, you just need to remove the red wire from the rear of the solenoid and connect it to the lead from the ammeter marked with a negative symbol, then run another wire from the other lead on the ammeter (the one marked positive) back to the connection on the rear of the solenoid. You cannot break the circuit at the ignition switch (or anywhere else in the headlamp shell for that matter) to connect the ammeter because the charge current from the alternator to the battery does not go through the headlamp shell.

For later machines, the situation is more complicated. The current from the alternator to the battery still connects in to the system at the rear of the solenoid but now, current from the battery passes through a seperate connection at the battery positive terminal. In order to attach the ammeter, you need to pick up both of these current flows and, in order to do that, you need to make some modifications to the wiring. If you were to break the circuit at the solenoid, as described above for earlier bikes, you would only measure current flowing from the alternator to the battery. If you were to break the connection at the second red wire to the battery terminal, you would only measure the current flowing out of the battery to the bike systems. If you were to disconnect both wires from the battery and connect the ammeter between wires and terminal, you would severely damage the alternator. The way to measure both currents is to either move the second battery connection back to the rear of the solenoid and connect the ammeter as above (This is not ideal, especially if electonic ignition is fitted, as any voltage drop on the main starter lead while starting would affect all of the bikes circuits and potentially cause starting problems) or remove the red charge lead from the rear of the solenoid and extend it to the vicinity of the battery, connecting the ammeter between the connected red leads and the battery positive terminal.

In any case, you will need to use good thick wires between the point where you break your circuit and wire in the ammeter... failing to do so will mean that you will have a significant voltage drop which will affect charging.

The other sort of ammeter is an electronic instrument. This will have three or four connections and there will be a seperate 'sensor' mounted in the vehicles wiring. This type of ammeter does away with the need to run heavy duty wiring between the instrument and the point where the circuit is broken but it is more complicated to wire in... and, needless to say, more expensive.

As to whether a voltmeter is better than an ammeter this really is a matter of choice. My preference is for the voltmeter, mainly for the simplicity of fitting and the fact that it is less likely to cause problems to the vehicle electrics.

Hope that helps, if I can be of any further assistance, drop me a message

Best wishes

Rob

[Ken in Oklahoma]

I'm sorry to have to say this but there is some poor information here. ...

Gee willikers Rob, did you really have to say it? That way? It sounded kinda harsh. Did you miss my caveat where I said that I might have missed something or said something that is just wrong. And that if I've blundered I hoped someone will catch it and correct it?

I am glad that you came along and set things straight. I felt like I needed to say something in order to give painter at least some kind of idea what he would be up against installing an ammeter.


Ken, touchy in Oklahoma

[painter.724]

WOW ! I had no clue that I could possibly run in to the senerios that I may face hooking this up . I pretty much thought that it would be just run a wire here,another there, and presto. Shows what I know! Please do not take this the wrong way, but I think I am pretty much scared into a volt meter. I either put my non working ammeter back in the hole in the fairing or get a volt meter and make it funtional. I believe I will do the latter. So since I am here I might as well keep asking the dumb questions. Will the BMW volt meters fit in a 2" hole Any ideas were to pick up a period correct if so, and how do I hook up a volt meter Ha !!! Oh, ME 109 I am pretty sure that it is just a cig. liter. BMW riders are much more refined and enjoy their smoke out of a bowl. Thanks Everyone for your help