Charging System ’90 Ultra

Question I have a 90 ultra classic HD and having trouble with the Harley charging system. When I start the bike, on the amp gauge, it shows 13 amps. When I turn the switch for the headlight it drops to 12 amps. If I use a turn signal or brake, the gauge will flickers back and froth. If I turn on the road light on top of everything else, the gauge will drop to between 8 and 10 amps. I believe the problem is in the stator, but how do I find out what amp stator I have and what size do I need to put back into the bike. Thanks for any and all help in this matter.

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Answer Randy,  The gauge you are reading is volts not amps. Are you using a Harley battery? Did you check input voltage? Put vdc meter across the battery pos and neg with mc at 2500 rpm should be 14 or 15 volts, refer to Touring Edition DVD and service manual. Do all 4 tests for 32 amp system which is what you have, maybe 22 amp. Split your production it doesn’t matter if it is working correctly , use test light with m/c off, unplug regulator in crankcase and ground test light /probe one side at a time the regulator plug coming from the regulator if the light comes on you have bleed back – regulator no good. If this is the case change all three pieces not one at a time. (you never rebuild a top end on a big block and not the bottom end – you will surely spin a bearing first time you go to have fun with it)Do all four tests in service manual if all checks out good, chances are battery connections where not tight enough (don’t be afraid to Loctite them – battery was not fully charged when installed) when doing tests remove spark plugs and rotate engine especially on the ohms resistance test to double check for a loose magnet on the stator. See what condition the plug coming out of the case is in, if it’s been soaking in oil a long time; might be money well spent just to upgrade all 3 pieces, I believe compufire or engine electronics offers a 38 or 42 amp upgrade or the 32 will work just fine . Also keep in mind all volt gauges will read 1 – 2 volts off due to voltage drop in an old harness with a long path to travel, not a worry , always check input voltage directly from the battery positive and negative.
Wrench Safe, FMH

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Harley-Davidson Charging System Removal
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11 Responses to “Charging System ’90 Ultra”
  1. James

    i have a 2008 ultra, sometimes when I start it the volt meter doesn’t come up to 13volts will read just under 12 v
    and the engine light is on if i turn it off and start it again sometimes it works right, today i was riding it was reading around 13v after a while i noticed battery light and engine light on , I stoped for a while when I was ready to go it started fine about a half while it quit charging 15 to 20 min later lights went out and volt gauge reads normal, also i have noticed when starting the engine light takes longer to go out I am thinking voltage regulator , guess i need to buy the electrical DVD

  2. johnny2012

    hello guys I have a 2012 flstn delux I am having charging issues battery is charge to 13.5 dc. crank motor over & runs dc volts drop to 12.5 dc at idle and it never climbs dc volts on meter . I bought the electric c/d from fix my hog it talks about a two wire charging system but I was looking at my connector it has 3-wire going into crank case. can I do the same test with a 3=wire test as i seen on c/d for a 3-wire if not can you help me out on this by giving me info on how two test if we have a back feed on voltage regulator. thanks for any info that you can help me with charging system.

    • Customer Service
      Customer Service

      Hi Johnny. The theory is the same. One more wire does not really change anything.
      When testing AC output test across any 2 (or combination of 2) wires.
      You should have 20 volts AC per 1k RPM.
      Same with testing stator ohms resistance. Test across two wires to see if resistance is within spec. Also use your meter to test each wire for continuity to ground.
      If lucky, you will only need to replace your regular.

  3. Jim

    Ticket 17675 i have a 2009 ultra that at start up shows 14 volts but after 10 minutes of riding when i come to a stop the volts will drop to around 12 volts if i take
    hi i have a 2009 ultra with a charging problem at start up i have 14 volts but after riding 10 mintes i apply the brake at a stop sign and my volts drop to around 12 volts if i release the brake my volts slowly return to 14 volts at idle battery has a full charge not sure where to start just had new stator and reg installed ????

  4. Brian

    I had ‘ 01 FLHTCI with a a Frankenstein trike conversion kit….my FrankenGlide
    was stolen…..not the issue.

    This was my first fuel injected bike…..ya it had the Magnetti Marelli module and after a through cleaning it performed flawless! NEVER an issue!

    So he MM haters just go suck it….😋

    Man was I supprised just how MUCH the fuel injection system just sucks power from the electrical system!!!

    IF there is a weak link in the chain it will surely leave you stranded on the side of the road eventually!

    I would recommend upgrading the electrical system on ANY fuelie bike!

    Not an issue for me now as I’m riding a ’79 FLH 1200 King of the Highway!

    She still has the OEM charging system and works perfect!

    Keep up the good work here fellas….. HAPPY NEW YEAR! Shovel on…


    • Brian

      When I first purchased the Shovel she was running spot on!

      One day went out to fire her up….just slow rolled over once…..?

      Pull the seat off and start climbing around and found some VERY
      questionable backyard hack “repairs”…..bad repair work, lousy wire routing!!….just stupid stuff! Pulled the battery and got to work.

      Rerouted a bunch of wiring, the main harness connector was cracked as someone did not move it to the side before mashing the seat back on! Just stupid, shoddy workmanship!

      Took my time, cut & replaced a few connectors and shrink wrapped
      them all! Crimped the connections….NOT soldered!

      The average weekend warrior can’t solder to save his life!

      And…..since my Shovelhead is 1979 vintage….it’s the last year the drivetrain is SOLID mounted!

      That’s right…NO rubber motor mounts So preflight checks are a MUST for this ol’ girl…not rocket science….ya get in to a routine and only takes 5-10 minutes every couple of runs.

      Used heat-shrink butt connectors at all splices and heat shrink
      wrapped all “eye” connectors also followed by heat-shrink wrap

      ALL these connectors are available at Home Depot!


    Hi I am working on a 2002 Electra Gilde with a two phase stator, my client originally had changed the regulator rectifier, I tested the generator/ stator and if showed continuity across the two wires and no continuity to the grounds where it was tested, I had to solder the stator wires to a new socket harness and installed a new regulator rectifier, I also changed the 40 amp circuit breaker and the charging system collapses when the bike reaches a certain temperature, I have tried several tests shown in the videos, but this bike simply won’t rectify and charge the battery, the battery gauge is moving from 12volts and dropping to 8 volts like if the rectifier was dead I desperate and do not know what to do could you please advise on this please FMH Team Inreally need your help!!!! David from Mexico