Turn Signal Troubleshooting

[hudson]

Hey guys - This is weird. On my 71 R75/5, my left side rear turn signal refuses to work. Tested/inspected old bulb (even put in the right side and worked). Replaced with new anyway. All other signals work, including the front left side.

I disassembled the brake light & turn signals as I needed to make a slight rear fender repair, taking note of the original connections, so I am puzzled... here is a picture.

BL Wiring.JPG (26.17 KiB) Viewed 1311 times

Do you see anything wrong? What does the green/red wire do?

I tested for voltage from brake light connections (black/white into brake light wire has 12v). When handlebar indicator switch is on per side, the voltage is carried over down to the rear bulb connections on each side. The RH side works, but the LH still does not. As a backup test, I even did continuity testing between the brake light connections to each turn signal- all is checking out, so no breaks in wiring between the two.

Has anyone ever come across this before? Any suggestions or tests?

Also, on the turn indicator relay in the headlight shell - What inputs should be used on the socket - 31 (two wires) & 56b (one wire) are used with a two prong relay. 56a is not used. However, it seems that if this wasn't correct nothing would work or at least one side wouldn't.

Thanks so much...

[Rob Frankham]

Point 1

Green/Red is the brake lamp, Grey/Black is the tail lamp. Right indicators should be Blue/Black and left should be Blue/Red.

Point 2

The designations shown in the wiring diagrams (i.e. 56a and 56b) are anomalous. These are shown on every circuit diagram I have for the /5 including the original BMW dioagram. According to the standard DIN codes, 56a should relate to the low beam headlamp circuit and 56b to the high beam. In addition, the circuit diagrams disagree with your experience in that they show the connection to the indicator switch originating from 56a not 56b as you describe. I think the only approach is to go back to first principles. On a two pin relay, one terminal is for the positive supply (possibly marked 31 on the relay) This should go to the ignition switch and will probably be a green/black wire (or just green if you're bike doesn't have fuses). The other wire should be green/yellow and go to the indicator switch at the handlebars. It really is that simple. I do agree with you that, if the wiring were incorrect, none of the indicatore would work so I don't think this is the source of your problem,

Point 3

If one of you're bulbs isn't working while all the rest are, it is a pretty good assumption that the problem originates in the wiring to that bulb. This means you are looking at the Blue/Red wire that leaves the connecting block in the headlamp shell and runs the length of the bike to the rear lamp housing, or the Blue/Red wire from the rear lamp housing to the indicator housing or the brown ground wire back from the indicator housing to the rear lamp housing. We can eliminate the ground wiring beyond the rear lamp housing because this is shared by all of the other lamps in the rear cluster and both indicators... if it was bad, none of them would work. Equally, we can eliminate the wiring from the indicator switch to the connection block because, if the fault was there, the front indicator wouldn't work.

You need to check the continuity of each of the three wires and there connections at either end, You also need to give some regard to the bulb holder. There are several ways to go about this. The easiest is to work through the circuit from one end checking the voltage at various points.

My first check would be at the rear light cluster looking at the voltage on the blue/red wire. This should go from 0 to 12 volts and back in time with the flashing of the front indicator. If it doesn't, there is a problem with that wire.

Given a good result here, I would check the voltage termination if the Blue/red wire at the indicator housing. This should also go from 0 to 12 volts and back. If not, that wire is suspect.

If this is still good, the next move is to check the voltage at the brown wire in the indicator housing. This should always be at zero (or thereabouts) whether the lamp is on or off. If it shows anything more than - say - half a volt, the brown ground is not connecting back to the ground in the rear lamp.

Finally, if you're getting good results in all of these places, the problem is with the bulb or bulb holder. I should add that all connections should be connected and the bulb should be in place when taking these readings.

Hope that helps

Rob

[hudson]

Thanks Rob! Great explanation and tips. I will give it a try...

[jagarra]

If your bike has the aluminum turn signal housing, the bulb gets the ground via the housing and the screws, I have had issues with a bad ground on the housing causing the signal not to work.

[hudson]

They are signals that I bought from a reputable business that sells aftermarket/reproduction BMW parts. They are exactly like the OEM signals. They are polished aluminum, however the reflector is cheap plastic and the two connections require soldering (verses the more heavy duty, old- school push in wire tabs. I will try the housing ground suggestion as well. I haven't had time to tackle the wire troubleshooting yet as Rob kindly suggested. Probably will get to this on the upcoming weekend. Thanks!