Another ST1100 Electrical Problem

Mb33ch

Joined
Oct 27, 2025
Messages
8
Age
31
Location
East Sussex
Bike
St1100m
Hi, I posted a couple of weeks ago about inspecting the waterpump on my 1991 ST1100M and got some very helpful responses. I decided after posting to also replace the timing belt as it had some wear. After waiting a while to get parts, I've put the bike back together (minus fairings) and was excited to run some cleaner through the cooling system and flush it a few times and ... I've lost all electrics.

At some point whilst trying to diagnose I did briefly have a connection, have lights on the dash and the starter kicked over. However apart from those few seconds I've had no electrics.

Jumping the starter solenoid does turn over the bike. I've already done the red wire bypass and I have voltage going to the connector by the headstock. I've also disassembled the ignition switch which doesn't seem to have any problems. The other wires on the solenoid also have continuity to there connectors. I've replaced the starter solenoid and no difference. Battery reads 13.1v to the ignition connector. Battery negative terminal shows low/no resistance to the frame so I think the ground is fine.

Is there something simple I'm missing? If any other point of the circuit had failed I'd still get some electrics working surely?
 
Usually when something like this happens it was something you disturbed in the area where you were working. In your case, I'd be very surprised if the fused link at the battery failed, unless you created a big dead short up front. More likely it is a disturbed connector, ignition wiring, or, as Phil suggested, the kill switch.
 
Would a bad kill switch cause no electrics? Ive tested all fuses in the main block, inline fuse from red wire bypass and main fuse and therell all fine, as is the ground from the fuse block.
 
Take a look at the three connectors under the tank shelter in the front close to the handlebars, they connect through a metal plate. I have seen these pull apart and cause these kinds of problems. The plastic on the connectors when it ages becomes brittle and the little tab with the hook that holds the connectors together won't hold the connectors together and they will come apart -especially if the wiring gets disturbed while working on the bike. On ST1100's I always tie these connectors together with a small wire tie to prevent this.
 
If you've lost everything that would make the main 30A fuse that's in the same connector area as where you did the red wire bypass the primary suspect, but I think if you're seeing power at the connector by the steering stem that might contradict a bad main fuse. I'd still check it anyway. Then, as UP suggested, probe the input wire to the fuse block, its a red with black stripe wire.

Do you have a schematic for the bike to trace things out from there? If not, here's one you can use.
 

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Side stand switch can cause issues, I carry a connector that I modified to deal with the issue. You can take the connector apart and jump the two green wires to bypass the switch.
Check the red wire bypass again, they have been known to fail over time.
 

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I had a chance to do a few more checks today. Power is making it through the kill switch and back to the connector by the headstock but not to the fuse box.

The earth under the grab handle was quite corroded but still had continuity to the negative terminal. I have cleaned it up. Earth on the reg/rectifier terminal is fine.

I can't actually get the side stand switch connector apart currently. Or the small black connector nearby with the black and white wires which does look like its potentially partially melted.
 
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