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94 K1100LT Fuse 5 blowing

 
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knwyman



Joined: 25 Jul 2017
Posts: 16
Location: Western MA

PostPosted: Fri Apr 20, 2018 10:02 am    Post subject: 94 K1100LT Fuse 5 blowing Reply with quote

Looking for some insight into fuse #5 blowing. The bike is now my buddy's & I don't have access to it right now, just trying to troubleshoot the circuit from a clymer wiring diagram. He got stranded on the side of the road when the bike quit. He found fuse #5 blown. Long story short, I went to pick him & the bike up from the side of the road but the trailer I borrowed was too high for us to get the bike into. I ended up using a 20 amp fuse to get him home but need to figure out why that circuit is drawing more than 15 amps.

According to the schematic, the fuse provides constant power to the motronic relay & the motronic computer itself. I had him disconnect the motronic unit itself & the fuse still blew when he tried to start it. This tells me that it's something powered by the mortronic relay but I'm having some trouble figuring out what that may be. It looks to me that the motronic relay coil gets it's ground from the side stand switch. I'm assuming once the motronic relay is energized, the fuel pump relay gets it's coil power from the motronic relay via the green/yellow wire so I'm thinking that the fuel pump relay coil is drawing too many amps which seems odd..

Am I reading the wiring diagram correctly? Any insights about this circuit that may send me in a better direction? I'm sure I can figure it out once I get a chance to work on it & see exactly how that circuit & relay works but if anyone has a better place to start it would be great!
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Kris

94 K1100LT
85 K100RS
02 Buell S3T
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Scott_Anderson
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Joined: 05 Sep 2006
Posts: 3117
Location: Central Iowa, USA

PostPosted: Fri Apr 20, 2018 11:18 am    Post subject: Reply with quote

You might check to see what size fuse is installed in slot #1, as it is fed from the motronic relay as well. You could pull #1 and see what your measured load is on #7.(or if the fuse blows)
Does this bike have heated grips? They are connected to fuse #1, but the design that got messed up is that the +power goes to the grips, thru the grips before the dash switch, then to ground(BMW changed this design eventually but I have do documentation as to when it was applied). The high/off/low switch is in the ground circuit.
It's not uncommon for the grip wiring to get damaged and blow the fuse.
Another potential to look for is a skinned/pinched wire to either of the brake switches as they also get fed from fuse #1(rear brake more common than front brake).
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1995 K1100LT 0302044
1997 R1100RT ZC62149
2017 FLHTK Ultra Limited
Garmin StreetPilot 2820
Garmin Zumo 550
Garmin Zumo XT
"One who does not ask questions is ashamed to learn" Danish proverb
1997 K1100LT 0302488(R.I.P.)
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Flying Duck
PsyKotic Waterfowl


Joined: 27 Jan 2005
Posts: 10082
Location: Bumf***, WA

PostPosted: Fri Apr 20, 2018 3:16 pm    Post subject: Reply with quote

Yes, #5 does power the Motronic and Motronic relay.

If the HGs are shorting then the #1 will blow first and the Motronic fuse should still be fine. (DAMHIK)

The fuel pump relay power(30) comes from Fuse #6 so an issue with that should not blow Fuse #5.
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93 LT (x2)
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86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
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knwyman



Joined: 25 Jul 2017
Posts: 16
Location: Western MA

PostPosted: Sat Apr 21, 2018 6:56 am    Post subject: Reply with quote

Thank you both. I find it odd that the 15 amp fuse wouldn’t blow with the motronic module disconnected but the bike runs fine with a 20 amp fuse in the circuit. I was the problem was a dead short but if that was the case, a 20 amp would’ve blown too. It’ll be interesting to see what’s going on once I get a chance to work on it!
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Kris

94 K1100LT
85 K100RS
02 Buell S3T
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Flying Duck
PsyKotic Waterfowl


Joined: 27 Jan 2005
Posts: 10082
Location: Bumf***, WA

PostPosted: Sat Apr 21, 2018 7:43 am    Post subject: Reply with quote

knwyman wrote:
Thank you both. I find it odd that the 15 amp fuse wouldn’t blow with the motronic module disconnected but the bike runs fine with a 20 amp fuse in the circuit. I was the problem was a dead short but if that was the case, a 20 amp would’ve blown too. It’ll be interesting to see what’s going on once I get a chance to work on it!


Yes, very odd that 15A will blow but a 20A survives.

One possibility is an intermittent short that just hasn't hit yet again with the 20A installed. Have you tried a 15A again?
_________________
93 LT (x2)
94 RS
86-97 K75F(K75/100/1100 Frankenbrick)
86 K75C w/paralever, hi perf cams,TURBO!
91 & 92 K75Ss
91 K1
86 custom K100
14 WR250R
IBA #17739 (SS1K, BBG, 50CC)
Buy parts HERE
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knwyman



Joined: 25 Jul 2017
Posts: 16
Location: Western MA

PostPosted: Sat Apr 21, 2018 9:53 pm    Post subject: Reply with quote

Flying Duck wrote:
knwyman wrote:
Thank you both. I find it odd that the 15 amp fuse wouldn’t blow with the motronic module disconnected but the bike runs fine with a 20 amp fuse in the circuit. I was the problem was a dead short but if that was the case, a 20 amp would’ve blown too. It’ll be interesting to see what’s going on once I get a chance to work on it!


Yes, very odd that 15A will blow but a 20A survives.

One possibility is an intermittent short that just hasn't hit yet again with the 20A installed. Have you tried a 15A again?


No, I haven’t had a chance to get into it yet but probably next weekend.
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Kris

94 K1100LT
85 K100RS
02 Buell S3T
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