Sprint St 1050 Bad Regulator/rectifier?

Discussion in 'Technical Help' started by Tim - Sprint ST 1050, Feb 25, 2026 at 5:35 PM.

  1. Tim - Sprint ST 1050

    Sep 25, 2025
    30
    18
    England
    Hey guys, some of you might remember helping me identify loose tubes which long story short also lead me to replacing the regulator/rectifier and the stator which allowed me to get back on the road and all was good but then after I went out to use it once more the bike would only start for one or two seconds and then would blow the main 30a fuse, after doing some research into what to test I think I may have found the problem but I was hoping for some expert advice to clarify, with the stator (3 black wires) disconnected from the regulator/rectifier (3 yellow wires) and the ignition on, I used a multimeter set to 20v and touched the black probe to the negative terminal on the battery and the red probe to each of the three yellow wires, I got a reading on the first yellow wire of 4.62v, on the second I got 4.61v and on the 3rd I got 12v and when the ignition was switched off those went up to 4.85 and for pin 1 and 2 and 12.8 on pin, from what I have found it sounds like there should be no reading between the negative terminal and each of the yellow wires and it sounds from my research like there is an internal failure within the regulator/rectifier (even though it has only been used once) could someone please confirm if there is anything else that I should be checking to verify this or whether that is confirmation enough please? The regulator/rectifier is a series mosfet from ultimate rectifier, part number is UR-SR-141-2374

    Thanks for taking the time to read all that, I know if was a long story but trying to be as detailed as possible, please let me know if I missed anything.

    Tim
     
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  2. joe mc donald

    Subscriber

    Dec 26, 2014
    15,991
    1,000
    slough / burnham
    @Tim - Sprint ST 1050 Tim you are not having much luck with your sprint. I am not sure on electrics. But hopefully one of the wise ones will pop along soon and assist.
     
  3. Tim - Sprint ST 1050

    Sep 25, 2025
    30
    18
    England
    Hey Joe,
    Thanks for stopping by, your right It seems to be one step forward 2 steps back but hopefully someone with some electical knowlage will be able to point out how to be 100% sure if it's the regulator/rectifier and I'll send it back
     
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