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Micro Relays


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Hello all, and happy holidaze. Great riding weather here in NorCal.


My 2004 R1150 RTP has about 4-5 microrelays in the "fuse box". They seem to fail with regularity. I've replaced the fog light relay and the load relief relay at least 2-3 times EACH in the last few years. I'm lucky that I had a bunch of spare relays left from my parted out 2003 RTP.


Last night, after swapping the horn relay for the load relief relay, in order to get home with lights, I did some investigation.


ALL THREE of my failed relays (saved from previous events) had the same failure- the primary coil pulled the armature down, BUT THE CONTACTS DO NOT CONNECT. I manually bent the tip of the armature, and was able to fix all three. This seems weird to me. Anyone have a suggestion.


Also, any options besides BMW ($17) to replace? The part number is- 61.36-1393412.


Thanks all!



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Evening Don


As a rule those BMW relays are pretty hearty, once in a while a failure but nothing like you are seeing.


With the pull-in coil not fully pulling the contacts together that sort of points to low pull-in voltage or a ground side issue.


You might want to monitor for full system voltage to the relay & good continuity on ground or low side.


On your load relief relay-- that gets it low or ground side through the starter solenoid.


Have you tried putting a KNOWN 12v across the pull-in coil on one of your failed relays to see if a good 12v volts will close the contacts?


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DR, thanks! Should have mentioned- I tested them on my bench with a charged car battery. No other load, just stout alligator clips right to the terminals.


After my "repair", they are back in the bike working.


This one confounds me.



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Just a shot in the dark here but is it possible that the problem is one of voltage regulation? Could an over-voltage situation cause a relay to close with enough force to deform the relay? Subsequent closings would be incomplete and reforming the contact would provide relief (for a while at least).

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Morning Don


Still a very strange failure mode.


Seeing as you have a RT-P I suppose it's possible that your bike sat around the shop before being sold off so possibly the relays were swapped out with other bikes as functional ones were needed for other operational bikes.


Any chance your bike has extra loads on the relay contacts causing contact erosion? Something like extra horns on the horn relay or extra lights on the load shed relay? Extra load on the contacts could erode & shorten the contacts.


You are just failing way too many relays for a normal BMW motorcycle.


You might find replacement relays at a local auto parts store. Those are just standard 4 terminal Siemens micro relays. They were used in some automobiles in the past.


If you install NEW relay(s) & those fail same as you are getting now then you definitely have problems. If new relay(s) last & don't fail then possibly your current relays were just a run of bad parts, or were swapped out when the bike was pulled out of service, or were overloaded at one time.


One thing I have found while working on old police bikes is don't assume anything is as should be & the electrics on those bikes are usually a nightmare.


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... possible that your bike sat around the shop before being sold off so possibly the relays were swapped out with other bikes as functional ones were needed for other operational bikes. ....

That was exactly my first thought.

There relays are usually rock-solid and rarely fail. Multiple failures are very unusual. This may be simply a collection of bad relays from multiple bikes.


Following on the thought that there may be a system-voltage related issue that's causing the trouble:

- overvoltage would not damage the contacts. Armature has a limiting stop.

- undervoltage could cause arcing (contact is not pulled tight). However, these relays have pull-in voltages in range of 8-9V; you'd notice other bigger problems if that was the case.

- finally, overload. That is a most-likely cause of contact erosion. Since OP reports trouble with several different relays in the box, I am having hard time believing that every one of his circuits is overloaded. Fog-light circuit, perhaps.




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Galactic Greyhound

Hi Don,


Check that an aftermarket Headlamp bulb has not been fitted.


The standard headlamp bulb wattage is usually around 60W but some aftermarket fitments can be as much as 100W. The consequence of this is that, although you get a brighter (and maybe illegal) light, the bulb draws a much higher current than the circuit was designed for with possible detrimental effect on wiring, switches and relay contacts.


The headlight is supplied via the Load Relief relay contacts.


Also check the bulbs fitted to the fog lights for correct wattage in case a similar thing has been done to them. The fog lights are not normally fed via the Load Relief relay but use their own separate Fog Light relay.


This may account for the problems with both these relays.



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Hi everyone, Took a break for Christmas, and just back to this thread. I wish some of your answers sounded right to me, and I really appreciate the thought that went into your replies. But,


both the '04 and the '03 (that I borrowed some relays from) came right to me from the Calif. Hiway patrol. Neither sat around being a donor bike. And the bike has totally stock lights, both high and low, and the fogs.


It could be the weird cop wiring, and overloads that occurred with lights, sirens, PA systems, etc. before I got the bike.


I'll just keep carrying spare relays. I did discover that the relays that have 3 prongs will fit the slot and work just fine, so I have an increased pool of spares.


Happy new year everyone- please ride safely and enjoy yourselves!



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Evening Don


Careful in using 3 terminal relays.


I'm not sure how those 3 terminal relays will function safely.


On the 4 terminal relay there is 2 12v power inputs. One is high amp battery direct (doesn't go off with the key switch) & the other input is through the accessory side of the ign switch.


The other 2 terminals are to the starter as a low & to the lighting & other fused circuits.


SO-- the starter terminal is a given & a must to have. And the power out to the lights & fused accessories is a given & a must.


So, that MUST leave one of the power input terminals being shared with the other. Here is the possible problem--


If the high amp B+ input is the shared one then the relay will always be energized & never shut down (unless engine cranking).


Now if the ign accessory circuit is the shared input ( & I presume this is happening) ALL the load relief lighting & accessory power is NOW being provided by & through the low power ign switch contacts & that will for sure over tax the ign switch contacts & probably overload the very small diameter wires on the switch circuit side. (you have lost the high AMP B+ input to the load relief relay).


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