Headlight switch also turns on brake light

[gspd]

Holy crap! You're turning 'Electrics 101' into rocket science.
This is way simpler than you think. Remember, there were no digital multi meters in the 70's.....
keep in mind, 10.44v, 11.24v, 12.30v, are all the same in this case, the differences are simply slight resistance differences in you old wiring. not a problem. Also,ignore minor mv readings, they are minor leakages that are only detected by your ultra sensitive digital meter and have no bearing in reality and would probably not even register on an analog meter.

btw - the blue/red and blue/black wires are for your turn signals, ignore them for now.

Ok here goes..

step 1 - make a proper 12v test light; Easiest way is to remove one of your turn signal guts and connect a wire to each of its terminals; touch one of these wires to battery negative, the other will light the bulb when touched to battery positive
This is your 'test' light. go to step 2

step 2 - Remove tailight bulb from it's socket and confirm that it is a #1157. (double filament bulb with uneven side pins). I've seen single filament bulbs and bulbs with even locating pins jammed into a 1157 type socket. To test the bulb, connect the base of the bulb to battery negative and touch one terminal, and then the other, to battery positive. one should light up bright, the other dim. if ok go to step 3, or report findings

leave tail light bulb out for the following tests

step 3 - check the GROUND circuit; ...Connect one test light wire to battery positive. Touching the other wire to battery negative, to any engine metal part, or to the brown wire, should all make the test light go on , if ok, go to step 4. or report findings

step 4- Check BRAKE light circuit... Connect one end of test light to battery negative, turn on ignition, apply brake, test light should ONLY light when touched to red/gr wire. it should not go on if touched to the grey wire. if ok go to step 5, or report findings

step 5 - Check TAIL light circuit...Connect one end of test light to battery negative, turn on ignition, turn on lights, test light should ONLY light when touched to grey wire. it should not go on when touched to the red/grn wire. post results back here and we'll continue....

sounds like you have a bad ground or some wires were reversed during the previous repairs. or maybe they mis-connected some wires while replacing the handlebars and/or removing the back fender. Make sure no wires are chafed where they go in and out of the rear subframe and that the connector for that harness (near your tool tray) is ok.

[Rob Frankham]

A very useful set of readings... I can say from those that there doesn't appear to be anything wrong with the wiring or switches... the readings are pretty much what I would expect from a bike of this age... which reinforces my thoughts that the problem liies at the rear lamp cluster.

First of all, we can forget the blue/red wires and the blue/black wires... they are the feeds to the right and left indicators and have no significance.

From your description and the readings, I am fairly convinced that the tail light and the brake light connections are swapped with the rider that it could be a bulb that has the connections reversed... not as rare as you might think. If you look at each of your descriptions, substitute brake light for rear light and vice versa, the situation they describe is exactly what you would expect to happen.

There are potentially three ways this could occur:

The most likel'y is that the connections have been transposed at the bulb holder. Bearing in mind that your local mechanic probably removed the cluster and the wiring when he worked on the rear fender, it's quite possible that he simply connected them up wrong.

I'm not so certain about the next possibility... I don't have a /5 to look at... but on later bikes, there is an inline multi connector which connects the rear light sub loom to the main loom. This is located near the front of the rear fender quite close to the battery. If, on your bike, there is a multi connector at this locations, it's possible, but unlikely that the connections have been swapped here... it would need the connectors to have been removed from the connector block but it is possible. If on the other hand there are individual connectors at this point, then there is always the possibility that they have been conected wrong. This should be easy to see because the wire colours should match on wither side of the connector. Finally...

I go back to the bulb.

I can see no other place in the bike wiring where the connections could be transposed and the symptoms aren't those I would expect from a ground fault.

My advice is to try a new bulb, just to eliminate that, then, assuming that doesn't fix it, check the colour continuity at the inline multi connector. If that fails then simply swap the green/red wire with the grey/black wire. I am fairly sure that will solve the problem.

One other issue is revealed from your test meter results. While I don't believe this has any bearing on the main fault, you may wish to have a look at it as a secondary consideration.

You are getting a fairly significant voltage drop on the green/red wire... the brake lamp feed... Your measurements show a voltage drop of 1 volt between the positive battery terminal and the end of this wire. This may indicate a failing wire, a dirty connection or a bad switch. If the cause isn't obvious, please feel free to come back to me and I'll try to talk you through a series of tests to track it down.

Rob

[gspd]

Hi Rob -
This is an electrical issue that you or I could probably resolve in a few minutes, if we were there in person.
It takes longer to explain how to fix it than it does to actually fix it.

I have had decades of experience trouble-shooting electrical systems, and this experience has taught me to disregard minor (less than 1 volt) voltage variations between readings taken at either point on a specific wire or circuit.
In the real world, these variances are not what will determine wether something works or does not work

Case in point, recently experienced on a brand new klx250); I installed a small digital voltage display to monitor battery voltage. Connected it via the ignition switch so it would go on and off with the key. After installing this voltmeter, voltage displayed seemed way too low; 12.2v with key on, and 12.8v engine running so I went to the dealer and checked on another brand new bike in the showroom, same readings. Go figure. 12.6v at battery positive went down to 12.4v at ignition switch input and then 12.2 at ignition switch output to coil.

Measurements taken directly at the battery with the same voltmeter on both bikes were 12.6 key on and 13.2 running indicating that everything is working perfectly.

I ended up connecting a wire directly from the battery to the voltmeter with a small toggle switch to turn it off when not in use.

Point to ponder: In a perfect world digital meters set on 'ohms' will zero when the probes are touched together or when testing an isolated circuit. In the real world they will rarely zero when testing a specific wire or circuit that goes through a harness with multiple connectors and or switches. This situation is exacerbated with age. Makes no difference in the real world.

[Rob Frankham]

Hi GSPD,

I'm afraid I can't accept for one moment that a 1 volt voltage drop in a 12 volt circuit powering a single 5 watt bulb is acceptable.... especially as the same circuit should be powering a 21 watt filament. Personally, I wouldn't accept a 1 volt drop anywhere on a bikes circuits, although I accept that, in a high current circuit like a headlamp, it may be difficult to eliminate. This isn't, however, a high current circuit.

If we do some vastly simplified arithmetic (simplified because a number of the parameters are unknown) we can get a ballpark figure for the drop with the 21 watt filament...

A 12 volt 5 watt filament will draw somewhere less than .5 amps.. let's say .4 to allow for the low voltage and the TCoR of the filament. This gives us a resistance figure of somewhere around 2.5 ohms for the unwanted resistance or series of resistances that are causing the drop.

If we drop that figure into a 12 volt circuit driving a 21 watt filament, then the drop is highly likely to be over 2 volts... probably well over. This isn't good for two reasons:

1) It will lead to a real reduction in lamp brightness and

2) If the drop is due to a single high resistance point like a partly broken wire or a corroded connector, it will cause a considerable amount of heat... say about 3 or 4 watts... and this will cause the issue to get worse, sometimes quite rapidly.

The best way to approach it in this case, is to first get the lamps working in the correct sense then check the voltage drop directly between battery positive and various points in the brake lamp circuit to establish the point or points where the drop is being caused.

As regards the vehicle voltmeter. Where I want the vehicle meter to show the battery voltage reliably, I run dedicated wires back to the battery terminals with a relay in the positive line switched by the switched positive line from the ignitions switch. This ensures that I am getting the most accurate reading possible.

Regards

Rob

[My72R60]

Hi Guys,

I replaced the bulb and the conditions are unchanged.

[gspd]

My72r60 -
try the other tests I suggested and report back.

Rob F said: "Personally, I wouldn't accept a 1 volt drop anywhere on a bikes circuits"
I fully comprehend what you're saying, and in a perfect world voltage checked at any 'hot' point on a vehicle would be exactly the same as at the battery + terminal. Unfortunately, it never is. There always seems to be a slight loss somewhere along the line, and not much can be done about it. Even on a brand new car, the voltage will always be slightly lower (as much as 1 volt is not uncommon) if checked at the power socket in the dash or dome light (or any other electrical circuit) than if checked directly at the battery. try it.
This situation usually gets worse with age, but does not interfere with any functions.
Put it this way: Is anybody going to troubleshoot and/or rewire their 2015 Lexus because the battery reading is 12.6v and the reading at the licence plate bulb socket is 11.6v? NO, they will simply replace the burnt bulb and call it a day.

Anyways, my point is that the slight voltage differences that my72r60 is seeing are not causing the problem he is experiencing. I also suspect, as you do, that the grn/red wire and grey wire were inadvertently switched.

oh, and PS Rob. If you are using an old school VDO /Motometer type analog voltmeter on your bike, it can be calibrated to exactly match your battery reading via a screw that is accessible through a small hole in the side of the housing. There is no need to add a relay (and its extra wiring) to get exactly the same reading at your battery and on your dash. I haven't noticed any calibration options on the digital voltmeters i've encountered.

[Rob Frankham]

I can see we're going to have to agree to disagree on this one... just a couple of responses though...

I can't accept that a voltage drop of a volt is acceptable... I have never found it difficult to bring it down below that in any automotive circuit. In a circuit drawing less than an amp, I would consider a drop of a quarter of a volt to be verging unacceptable. As a general rule, it comes down to cleaning contacts and occasionally replacing crimped connectors if they've become corroded in the area of the crimp. If the drop is across the length of a piece of wire, then it definitely indicates that the wire has issues, probably a partly frayed or corroded conductor inside the insulation, which is going to get worse rather than better.

If you look at a higher current circuit, with a voltage drop of - say - 2 volts then the power lost is quite large. For example, a 2 volt drop with a current of 2 amps would indicate a power dissipation of 4 watts. If this is distributed along the length of the conductors to the load, then that isn't too dramatic although it does mean you're wasting that much energy. If, on the other hand, it's concentrated at one bad connector or one partly broken wire, then it is being dissipated at a single point. The wasted power will always appear as heat and 4 watts is the sort of power you would expect from some sets of heated grips... but concentrated at a single point. This can cause problems ranging from the catastrophic (e.g. a burned out wire or melted connection) to the cumulative (e.g. hardening of the insulation and increased corrosion). It is well worth tracking down and eliminating resistance spots, espcially in older machines.

Using the adjustment on a meter to compensate for inefficiencies in the wiring is anathema. The idea of a voltmeter (or any other sort of meter) is to tell you what is actually happening not to confirm what you want to think is happening. I know that the Motometer instrument on my 'RT reads accurately within visual limits so when it shows 14 volts, that is the voltage at the battery terminals. I know that the digital meter on my 'RS reads accurate to within .5% so when it shows 13.6 volts, that is what is happen ing at the battery terminals. I know that the older Motometer instrument on the R60 reads visually slightly low... less than 10% so I know when it is reading 13.5 volts, the actual reading is around 13.6 volts. I know these things because I have cross checked the meters using a Fluke DVM and an adjustable bench power supply. If any of these readings change significantly, I know that something has changed in the charge circuit and it needs to be checked. You may consider this to be a bit anal but that is what the meter is for. If it doesn't actually tell you when things are starting to go wrong, it's just a pretty ornament to fill a hole in the fairing dash.

The reason I run an additional independant circuit for the voltmeter is because I want it to tell me what is happening at the battery terminals, not at some point in the circuitry where the current path has been shared with all of the bikes circuits and where parts of that circuit might be carrying more than 10 amps (with the attendant inevitable voltage drop) or considerably more if high current accesories are in use. The most important point is that, when it is tacked into the circuit a long way from the battery, the reading will vary independant of battery voltage as a function of current consumption of the total circuits that are active on the machine. To my mind, reducing the number of variables that effect the reading is more important than the empiric reading of the meter as the best way to interpret the performance of the charge circuit is by comparison of readings.

Rob

[gspd]

Rob- Everything you said is 100% correct, you know your stuff, but I would like to add 2 things...
For me, the passing decades have reinforced these basic theories and procedures that were ingrained (indoctrinated?) during factory sponsored VW/Porsche training seminars in the '70's and routinely applied ever since. The more things change, the more they stay the same.

1) If you earn your living working on automotive electrical systems (which to me are the same as motorcycle systems but with more bells and whistles) you will learn to totally ignore voltage drops of around 1 volt. If you don't ignore them, you will go friggin' nuts and never get anything fixed, as they are the rule, rather than the exception. There is no practical cure. Tracing the exact location of these losses is pointless, not to mention virtually impossible, because they are most likely lurking deep in a main wiring harness.
Voltage drops of 2volts, 3 volts, or more, will usually be caused by, or accompanied by, something not working right. They will usually be preceded by repeated attempts at replacing the same burnt fuse.
Note: Always take smoke and fire seriously ; ).

2) ...the older Motometer instrument on the R60 reads visually slightly low... less than 10% so I know when it is reading 13.5 volts, the actual reading is around 13.6 volts The calibration adjustment on old school analog voltmeters was there for a reason. You could easily adjust your needle to indicate 13.6v instead of compensating for the meters' inaccurate display in your head. Problematic voltage variations will still be reflected accurately. It is no different than repositioning your speedometer needle to indicate actual road speed, instead of constantly mentally compensating for a known too low or too high speed reading.

[Rob Frankham]

As I said, we'll have to agree to disagree... You're right... we have hijacked the thread but I don't feel too guilty. I received a PM from MY72R60 (apparently for some reason he can't post on the forum) to say that the issue is resolved... swapped connections as we both expected, so we aren't stealing his thunder as such, just having an interesting exchange of ideas.

[SteveD]