R75/5 Headlight Power

[hudson]

Hey guys- I want to put a relay in my headlight for better lighting. My 71 R75/5 doesn't even have fuses. Plus there are wiring revisions from the previous owner, so not every single wire color or connection jives with the schematic. It doesn't have the OEM terminal board. I guess you would say that everything is wired directly or through wire connection blocks.

I followed the headlight wires from the handlebar switch. I am trying to figure out which wire is the power source that I should interrupt for the relay. The relay has connections for interrupting between the headlight wires (both low and high beam) and also a ground. I just can't determine which is the power wire I should tap into. There are not many wires that come out of that particular loom. I see a green/red wire and I am initially thinking this is the one.

In the picture in the forefront is the headlight white/yellow and brown ground wire that split off the loom from the switch. I got that. But you will also see two other wires at the top left that are yellow and a red/green wire that feeds into a wiring block. I was thinking red/green is the one power wire from the headlight handlebar switch.

I would like to put small fuses in as well, but have no idea what wires as things are somewhat altered. What wires should they trace back to? If I know the origin, I guess I can go from there and trace back to the headlight shell. The colors may be totally different from what is in there .

Any help is appreciated...

Headlight wires.JPG (35.72 KiB) Viewed 1144 times

[gspd]

Hudson said "I want to put a relay in my headlight for better lighting."

Adding a relay will not give you 'better lighting' per se.
What issue exactly are you trying to resolve?
If your bike still has the original old 'one key fits all' key that you push down for ignition and then turn to the side to turn on the headlight, the contacts in that switch are as heavy duty as most relays.

However, if you insist on adding a extra relay...
a standard 4 terminal relay can be had at any electronics store for $3.
the simplest way to hook it up is
terminal 85 to any good ground
terminal 30 direct to battery positive (in line fuse at battery recommended)

the yellow/white oe wire is the one you have to interrupt
(it is the wire from the ignition switch that has power only when the headlight is turned on)
disconnect both ends that connect in block in the headlight
the ignition switch end goes to terminal 86
the handlebar (hi/lo beam switch) end goes to terminal 87

but seriously... What issue exactly are you trying to resolve?

[Rob Frankham]

I'm not quite sure what you're seeking to achieve. Is it increased power at the headlamp? Do you want to protect the switches? Are you intending to fit a higher wattage bulb? or are you trying to emulate the load shedding function of the relay on later bikes?

It's difficult to advise on what you need to do unless we have this information.

FWIW, this is a description of the circuit as fitted by BMW.

*Power is provided to the ignition switch via a Red wire. This feed is shared with all of the bikes circuits and is sourced from the starter relay.
* It is taken from the lighting section of the ignition switch to the handlebar switchgear via a wire coloured yellow/white.
*At the handlebar switch (dip switch) it is routed one of two ways. 1) via a white wire to the main beam filament and 2) via a yellow wire to the dip beam filament.

As you have said that some of the wires may have been replaced, the wire colours may not be correct and there is also a possibility that the circuit has, in some way, be rerouted. I'm afraid that the only way to tell is to follow the wires and see where they go.

Sorry if that isn't very helpful... if you can provide a bit more information, I'll try to help further...

Rob

[hudson]

Sorry -Yeah it is just the push down key, side to side as you mentioned. May have left out that I am putting in an aftermarket H4 conversion kit. I keep reading that individuals who have done so have installed a relay. I guess it can help current protection and may help with brightness. I bought one of those small matchbox relays. Attached is a picture of it and shows the inputs/outputs. The middle connection (12V power in) is the question I have for the right source of power. I can do all the rest no problem. I need to tap into a 12V source.

I have to tap into a power wire and branch it to this relay's power in. So are you saying either the red wire from the ignition switch or the yellow/white from the headlight switch on the bar are my choices?

Thanks.

Matchbox.jpg (71.09 KiB) Viewed 1099 times

[Rob Frankham]

Actually, I think you'll find there are two relays in that box, one for the main beam and one for the dipped beam. For the 12 volt power source connection, you should go straigcable capable of carrying at least t back to the battery positive terminal with a wire capable of carrying at least 10 amps (preferably 15 or 16 amps). That would be around a 1 square millimeter conductor. It is a very good idea to put a fuse in the wire between the relay and the battery, preferably as close to the battery as you can for maximum protection.

Rob

[gspd]

No wiring/relay mods are necessary if you are switching from the stock 40/45w setup to a 60/65 h4 setup.
as long as your wiring is good.

If 'better lighting' is your ultimate goal, mount two of these to your lower triple clamp and leave your headlight in the 5w parking light mode.https://www.aliexpress.com/item/4001111 ... hweb201603_
total consumption will be 25w.
you'll be able to see where you're going amazingly well at night, and your electrical/charging system will thank you.

[hudson]

Ok Rob - forget the splice and go directly from battery, with a fuse, I appreciate all of the other tips as well gents!

[Rob Frankham]

Ok Rob - forget the splice and go directly from battery, with a fuse, I appreciate all of the other tips as well gents!

AS a general rule, if you're fitting an accesory relay, it's always better to go back to the battery. One of the main purposes of the relay is to protect the switchgear from high currents. The relay (well, OK let's be precise, a type A accesory relay) doesn't consume or pass any current when it isn't activated so there's no reason to isolate it through the ignition switch.

Rob

[gspd]

Just a thought...
To increase cranking power, your starter relay is designed to cut power to the headlight circuit when the starter is activated.
You may be eliminating that function depending on where you intercept the headlight circuit for your new relay setup.
Make sure that it still functions correctly, or manually turn off your headlight before activating starter.

[Rob Frankham]

Just a thought...
To increase cranking power, your starter relay is designed to cut power to the headlight circuit when the starter is activated.
You may be eliminating that function depending on where you intercept the headlight circuit for your new relay setup.
Make sure that it still functions correctly, or manually turn off your headlight before activating starter.

This doesn't actually apply to /5 models which have a very different starter relay and wiring. It could probably be done but it would need a study of the circuits to ensure that it didn't interfere with the starter interlock circuit.

Rob