F700GS 12 V interruption

**bolter1100** · 08-01-21

I'm puzzled here. I installed LED aux lights on my 700GS with an external switch and they are wired directly to a switched terminal on an Eastern Beaver PC-8 which, in turn, is connected directly to the battery.

It works fine but I recently discovered the lights will turn off randomly. The light in the switch stays on.

I checked the security of the leads where they are connected and wiggled them to see if that would trigger a turn-off but it doesn't. Could this have anything to do with the CANBUS system?

**bmwroadsterca** · 08-02-21

Absolutely not.

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**bolter1100** · 08-06-21

I didn't think so either but I have since found out that Eastern Beaver sells a diode to be used in connecting the relay up direct to the battery. I don't think the diode was available when I first bought the PC-8 - but I might have overlooked it.

Supposedly the diode is there to keep the wiring from feeding back voltage that is read by the CANbus system.

I think I need a wiring diagram but I can't seem to locate one.

**bmwroadsterca** · 08-06-21

Originally Posted by bolter1100

I didn't think so either but I have since found out that Eastern Beaver sells a diode to be used in connecting the relay up direct to the battery. I don't think the diode was available when I first bought the PC-8 - but I might have overlooked it.

Supposedly the diode is there to keep the wiring from feeding back voltage that is read by the CANbus system.

I think I need a wiring diagram but I can't seem to locate one.

No the diode is there to suppress the back EMF that results when the relay coil circuit is interrupted otherwise that voltage spike could cause damage.

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**bmwroadsterca** · 08-06-21

And I dismissed the CAN-bus from consideration because it is a data comms network that is often confused with the ZFE's function in controlling chassis electrics.

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**rcb78** · 08-07-21

Where are you getting switched power from to turn the unit on?

**bolter1100** · 08-07-21

BMW and rcb, that's good info. I won't have access to the bike until early next week and I'll answer then. Thanks.

Harry

**ccramerusc** · 08-08-21

I have a set of auxiliary LED lights running through an external switch and through my PC-8. Never had a problem with it/them. I would guess that your problem is in the lights themselves, or wiring downstream of the switch. I say that because the PC-8 shouldn't be causing the problem and it sounds like you have power to the switch.

BTW, I have the relay for my PC-8 tied into the low bean circuit. That way my accessories only are powered when the engine is running. I use the switched side to run LED lights, air horn, and heated jacket/gloves. On the direct side I have my USB port and the pigtails for my charger. I use the GPS line to power my dash cam and voltmeter.

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**bolter1100** · 08-09-21

Thanks for the replies, guys. I got a chance to re-visit the problem today and I have the aux light switch connected to the aux power tap under the tank cover. This is the one where you have to purchase the pigtail from BMW and connect it to the empty plug.

While under there I spliced in a diode in that same line as that seems to be the only place that connects back to the ZFE (CABbus).

We'll see what happens now. Of course I couldn't duplicate the problem either before or after the "surgery"

Thanks again for your input.

Harry

**rcb78** · 08-09-21

Ok, so here's the thing with pulling power from that location, if your battery voltage falls below a certain threshold, the ZFE (there,, happy people?

) will shut it down until the voltage comes back up. So if that is your trigger wire, that means the unit will still have power coming in from the main feed, but the switched feed will shut it down. Easy check with a volt meter, turn everything on and see what happens. My Aux lights were wired this way and would shut off from time to time. Could be battery, R&R, stator, or any combo of those. For me, a new battery and R&R did it.

**ccramerusc** · 08-10-21

Now I'm confused. Are you using the GPS power tap to switch on the relay for the PC-8? That is a very common use for it. In that case, everything should work fine, and the light circuit you added will be completely independent of the bike's computer, meaning that there is no need for a diode. This is how the PC-8 (or any fuzeblock) is designed to work. The fuzeblock itself is connected directly to the battery and provides separate circuits to be added independent of the bike's computer. All you need is a very low level of switched power to switch on a relay to connect the fuzeblock's circuits to the battery. Again, the GPS power tap is great for this. The only thing that could cause the computer to turn off that GPS power tap circuit is if it drew more than 5 amps, or possibly if the overall power system dropped very low in voltage. In either of those unlikely scenarios, the power being cut by the computer would cause the relay to close, thus disconnecting all the circuits of the fuseblock. This can't be your problem because you said the light on the switch you added (on the circuit you added) remained on while you were having your problems, indicating that the circuits of the fuzeblock remained powered.

**bmwroadsterca** · 08-10-21

Originally Posted by ccramerusc

Now I'm confused. Are you using the GPS power tap to switch on the relay for the PC-8? That is a very common use for it. In that case, everything should work fine, and the light circuit you added will be completely independent of the bike's computer, meaning that there is no need for a diode.

In that case the GPS power tap (from the ZFE) powers the relay coil and this is exactly where the diode comes into play. It is the relay coil that generates the back EMF spike when power is interupted to it. The ZFE may not tolerate the spikes or it may but it is better to be safe.

https://en.wikipedia.org/wiki/Flyback_diode

**bolter1100** · 08-10-21

I don't think it's the battery as it was replaced about a year ago but I did not check the voltage at the switch lead. The puzzling part is that the light in the switch remains on even when the lights go off.

I agree with bmwroadster's assessment that installing a relay in that line should be a preventive. I guess we'll see what happens.

Thanks everyone for your responses. I'll let you know what happens.

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