VT1100 5v on circuit with fuse pulled

• fuel pump
• Electrical
• VT1100

• DH

  Daniel Holmstrom

  8/12/26, 4:12 PM

  '98 Spirit.  Replaced fuel pump 4 months ago with cheap Amazon crap.  On way home last week bike blew ignition fuse.  I limped it home but the cut-off relay was melted by then.  Jumping the relay connector runs the pump and then immediately blows the fuse.  Assumed the pump was shit (because it is)  Disconnected pump and noticed the voltage coming into the connector was low (11.8 vs. about 13 at the battery).  Disconnected ignition fuse and am getting 5v at the cut-off relay connector.  It is coming from the tail/meter circuit.  I have just spent 10 hours pulling every connector apart on the bike and am just as unsure as when I started.

  1. Can someone verify that - with ONLY the ignition fuse pulled - there should be ZERO or close to zero volts going to the relay?  And that the voltage going to the relay when healthy should be more or less the same as the battery? (ignition ON)

  2. Is there ANYWHERE on the bike where 5v makes any sense?  Because it doesn't to me.

  3.  My assumption is that there is a partially open circuit somewhere bleeding voltage into the ground.  When I unplug both front turn signals, I lose the 5v.  If I disconnect the Iginition Control Module, I lose the 5v.  Am I looking for a short between the signal connectors and the ICM, or is there a chance my ICM is bad?

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  TJ Admin Staff member

  8/27/26, 6:08 PM

  @Daniel Holmstrom Ignition fuse pulled: on the relay's black switched-power wire, I would expect essentially 0 V. With the fuse installed and ignition ON, I would expect approximately battery voltage — e.g. 12.2–12.8 V on a charged battery this is without the bike running. 
  
  

  Not as a normal regulated 5 V reference circuit like you'd find on an EFI motorcycle.

  This is a carbureted, transistorized-ignition bike. There isn't an ECU with TPS/MAP/etc. running from a conventional 5 V reference bus. So if you're finding a stable 5 V on what is supposed to be the 12 V ignition supply, I would absolutely regard that as abnormal.

   

  However, a digital multimeter can very legitimately display 5 V on a circuit that isn't actually capable of supplying 5 V. That's the classic backfeed/phantom-voltage situation. Your meter has extremely high input resistance. Current can sneak through:  ICM electronics - coil windings - relay electronics- indicator bulbs - turn-signal filaments - another circuit …and the meter just happily says: 5 V even though there's almost no current behind it. So there is a huge distinction between: "This circuit is producing 5 V" and  "My meter sees 5 V on this floating circuit." I strongly suspect you have the latter.

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