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How to Bypass your EHC to power your ignition

Discussion in 'How-To' started by Moespeeds, Oct 21, 2008.

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  1. Moespeeds

    Moespeeds Well-Known Member

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    Everyone has been bitching about their EHC crapping out lately, and in the past year I have lost my horn and headlights. I let the horn go, and direct wired my headlights. Well in the past 2 weeks I had a couple of breakdowns with no power to the ignition system. I traced the problem to the EHC, and tonight decided to go ahead and bypass it completely. I don't have a stock ignition, I swapped it out for a Dyna 2000i in the spring, but the concept is the same, you simply have to determine which wire to the coil is bringing 12v from the EHC, and replace that wire with a reliable 12v switched source. I took a few pics below.

    [​IMG]

    First you need to determine which of the wires on the coil is bringing power. mark them so you know what goes where, then disconnect them one at a time and test them. You will need to test them with the key in the "on" position, and hit "run" on the bars. This tells the EHC to send power to the coil. On my bike, power was coming in on the front coil.

    [​IMG]

    [​IMG]

    [​IMG]

    Once I determined which wire was the hot, I used heat shrink tubing to cover up the old wire from the EHC. Who knows if you might need it later.

    [​IMG]

    A new wire was run from the battery compartment, down through the harness, taking the same route as the stock ignition wires. I crimped off a terminal so it could be attached to the coil where the old EHC wire was. Leave the coil cover off until you are finished with everything, so you can test your new connection for 12v.

    [​IMG]

    The last step is to run the wire in the battery compartment through a switch and a 15a fuse. You can pull power at this end from any connection that has continuous power when your key is on, but then you are once again at the mercy of the EHC. For instance if you power it from your running lights, and you lose that function on the EHC, you will lose your ignition. The other option is to run the line directly from the battery. The problem here is that in the unlikely event that someone figured out that your ignition is switched, they could turn it on and push start your bike (starter won't crank without the key in). A better way would be to replace bigdog's bullshit key switch with a regular 12v key, and just pull power from there. This would eliminate the need for a switch under the seat, and is the most secure way to do it, but I was too lazy for that tonight. Your "RUN" switch on the bars will no longer do anything, you will simply flip your switch under the seat instead.

    [​IMG]

    This is a down and dirty, reliable, and cheap way to get by should the "run" function in your EHC fail. I hope this helps someone.
     
  2. lee

    lee Well-Known Member

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    good work Moe
     
  3. Moespeeds

    Moespeeds Well-Known Member

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  4. bdmridgeback

    bdmridgeback Low Down Chop Shop

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    Might be just as easy to buy the Sportster ignition switch, and power the EHC and a separate wire from the switch directly to the coil. Then you only have one main battery feed to fuse and hook to the battery from the new switch.

    Doing it that way, without the separate switches, you'll be one step ahead when the EHC completely fails and you have to put a Wire-Plus module in it. You will need the new switch at that time anyway, and the extra toggles under the seat are just one more fail point that you won't need.

    Just my .02! :2thumbs:
     
  5. Moespeeds

    Moespeeds Well-Known Member

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    If I had the time I would have done it that way, I didn't realize the Big Dog key switch wasn't 12v until I took it apart last night, and I only had what was lying around in my garage. The goal was to just get it running, I can tweak it as time allows.
     
  6. Throttle Jockey

    Throttle Jockey Don't Look at my Member!

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    I bet the guys that change out the EHC will get a lot more horsepower. Has anyone checked it out?

    TJ
     
  7. Moespeeds

    Moespeeds Well-Known Member

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    How could you get more horsepower? The EHC isn't controlling timing or anything else directly related to running the engine, other than sending power to the components that do?
     
  8. Throttle Jockey

    Throttle Jockey Don't Look at my Member!

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    Dont you change the ignition system out too when you do it?

    TJ
     
  9. barhopper

    barhopper Another round please

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    I just put in a bigger battery, now the thing hauls ass. :roll: :roll: :roll:
     
  10. bdmridgeback

    bdmridgeback Low Down Chop Shop

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    You do not have to change the ignition when you eliminate the EHC. I did, I bought a programmable Thunderheart that is just like the one that is in the BDM's from the factory. Only difference is that BDM programs a very mild ignition curve in it to pass DOT regulations.

    Mine runs noticably better since I swapped it out and I have not even plugged a laptop in yet and played with curves to get it better.
     
    #10 bdmridgeback, Oct 23, 2008
    Last edited: Oct 23, 2008
  11. Throttle Jockey

    Throttle Jockey Don't Look at my Member!

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    Thats what I'm talking about. It makes sense to me that if we do the upgrade it would be worth it to get this thing runnning like a crate motor. An SS 117 out of the crate will run like a scalded arsed ape.

    TJ
     
  12. Moespeeds

    Moespeeds Well-Known Member

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    I changed to a Dyni 2000i Single fire, it made a big difference in the way the bike runs. Smoother idle, better power. I'm not too crazy about horsepower so I never cared much, but without a doubt changing the ignition was a nice upgrade.
     
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