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Sportster '07-'09 ECU relocation

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So if you own an '07-'09 Sportster and have ever considered changing up your rear guard &/or seat you have probably wondered what to do with the ECU fitted in the rear guard under your seat.

There are a bunch of different ways this can be done, so to help out anyone considering this we thought that we would post up a few pics of what we did on our '09 Sporty.  The most common relocations either fit the ECU under the LHS battery cover or relocate it to behind the rear cylinder.  We went with  behind the rear cylinder as this is where the later model Sportsters have the ECU and didn't require any trimming of the ECU or battery replacement.  By no means do we claim this to be the best location or easiest solution - we are simply providing some info on what we did.

So here goes:

  • Strip that seat off so that you can see what you are up against.  This will expose the rear guard ECU insert plate and wiring loom.  Also open up the LHS cover (to where the battery and fuses are located) and pull out the master fuse (or disconnect the battery negative) so you don't accidentally damage something.  Dont be surpised if that security system does a little beep when you pull the fuse - this is normal
    • Now you can pop the ECU out of the plastic holder in the rear guard.  It just has a couple of tabs you need to hold back and it will slip off the locating posts and you can unplug the wiring plug.  At the same time also remove the security connector from this plastic holder (located just above the ECU and is about an inch wide by 3" long)

    • Now at this point we just pulled the ECU and security box forward and hung it over the LHS of the bike out of the way.  This is because we were changing over the rear guard at the same time so wanted to get it out of the way for this next step.  Likely if your moving the ECU your also changing the guard so we will put some steps/photos in below regarding this.  If you just want to move the ECU skip ahead a few points

    • Now before you remove the guard you need to disconnect the rear lighting wiring loom.  With the seat off you will probably be able to see the connector located under the seat area in amongst the frame.  If you cant spot it find the wiring penetration in the guard (located just below the ECU plate on the LHS of the bike down near the frame) and trace the wires from there.  You need to unplug this connector so the guard will come free of the frame
    • You also need to disconnect the OEM rear indicators if they are mounted off the fender struts (and through the rear guard side panels)
    • To disconnect the indicators you need to remove the OEM stop/tail light and behind that you will find the rear lighting circuit board (see the photo below).  The indicators are the two 2-wire plugs (purple/black) located just off the centre of the board.  Disconnect these indicator plugs and at the same time you can disconnect the remaining plugs (plug on the RHS of the photo is the main wiring loom out to this control board and the one on the LHS is the stop/tail light)

    • Once the indicator plugs are disconnected (from the lighting board shown in the photo above) you can pull the wires back through the hole(s) in the guard, unclipping the wiring from the locators under the guard as you go.  Once back to the indicator you can unbolt the mounting arms and remove the indicators (complete indicator, mounting arm and wiring will pull free of the bike)
    • With the indicators removed and the wiring loom disconnected you can now unbolt the guard: You have the large seat locating lug under the seat (uses a Torx fitting) and two bolts either side of the guard that fix to the fender struts.  The guard should then be able to be lifted out of the way (may be easier to drop the guard down onto the tyre and rotate it out depending on clearances and how your bike is sitting/jacked)

    • When we took off the guard you can still see the main rear lighting loom cable running through the rubber conduit under the middle of the guard.  In order to  get the cable out of this conduit (without just cutting it open) we decided to pull the plug off the rear end of the cable and just feed the cable back through (as we were going to cut these cables to suit the new light positions anyways).  The plug is the one shown below

    • To get the plug off there is a clip at either side (near where the cables enter the plug) that you need to disengage and then it will allow you to swing open the locking section at the rear of the plug.  To get the individual wires out you need a small screwdriver (or some o ring tools or something else small and pointy - a paperclip might even do).  You need to insert it its the slots either above or below (depending on orientation) the wire entries.  It should depress the clip that is inside of there and the wire will simply slide out of the plug.  It does take some wiggling around sometimes to find that sweet spot, but when you hit it the wires will pull out easily
    • Now that your wires are free and guard is off lets get back to relocating that ECU
    • There are a bunch of different way and places people relocate their ECU - so we are not claiming by any means that this is the best way to do it, it is simply the way we chose to go.  A very common other way to do it is to relocate the main fuse and connector plug off the battery mounting plate and fix the ECU under the LHS cover there (running a smaller battery will aid this).  We chose to put ours between the frame and the rear Jug which is where they are located on the later model Sportys (Iron's and 48's)
    • To do this we pulled the wires under the frame and over the top of the battery (out to the LHS of the bike).  Removing the battery securing clamp will aid this process as it will allow you to jiggle the battery and get the cable with that large ECU connector through.  We didn't need to disconnect the battery to do this, but we did slide the battery out a bit to give us some more room

    • Once the cable was pulled through and sitting neat over the top of the battery make sure that you have the connector plugged into the ECU and feed it in between the rear jug and the frame.  In the photo below we have previously relocated the ignition switch to behind the rear jug - so there is a little less room for us to feed the ECU through however it was still easily done.  If you have your switch in the OEM position near the neck you will have heaps of room
    • If you wanted to fit up the ECU under the battery cover (instead of behind the rear cylinder) at this point you would relocate the main fuse and connector plug and mount up the ECU to the side of the battery.  Depending on how you do this some people remove the battery securing bracket (to give a touch more room), trim down the ECU locating lugs and then fix the ECU to the battery using double sided tape or zip ties).  You then also need to find a position for the main fuse and connector plug (may also tuck under this side cover or need to be tucked in behind the rear cylinder).  From what we know it is a snug fit so getting the cover on might take some negotiating (and perhaps a small zip tie to hold it closed).  If you can get a smaller battery this would be wise as will give you some more room to fitup all these parts under that LHS cover.  Anyways this was an aside - back to our job

    • With the ECU tucked in behind the rear cylinder you can now jiggle it into a good position where it sits back away from the cylinder fins.  We simply secured ours with zip ties, through the ECU mounting lug holes (at the corners) and and around the frame or other wiring loom at the back of the ECU.  The key here is to keep a good air gap between the ECU and the rear jug/exhaust so that you get some good airflow through the area to minimise the chance of overheating the ECU
    • The photo below shows the ECU as seen from the RHS of the bike (securing of ECU still in progress)

    • Given we have a wrapped exhaust on this bike (and no other heat shielding) we thought that we would make up a little heat shield to protect the ECU a little more.  We went for a really simply option and just split a piece of 2 1/4" diameter tube (around 130mm long) and welded two half chain links on the inside.  The half chain links gave us something to use to fix the shield to the exhaust, with the aid of a couple of SS hose clamps.  With a couple of coats of heatproof matt black paint it was ready to be installed.  I'm sure that you could make up something a little fancier than this if you need to (or may not fit anything at all).

    • For reference the 883 Irons and 48's have their ECU mounted in this position in a small plastic case.  Potentially you could grab one of these plastic cases off ebay and fit that up to provide some heat protection if your looking for simple and well proven solution
    •  To finish up - close up your LHS cover and you are good to rock and roll (unless your changing up your guard - then you better get back to that first!).  Your LHS cover should close up snug with the ECU wires coming out of the top LHS notch out (where there were already wires previously).

    • Running the bike with the ECU here we have done around 5000kms thus far without issue.  Surface temperature of the ECU gets to about 65-70 deg C once you stop the bike and there is no airflow to keep the unit cool
    • For those of you changing over your rear guard - now that the ECU is in place you can get back to that task and fit-up one of those night short Easyriders guards and a little solo seat or whatever tickles your fancy.
    • If you are going to be running a stock guard and lights you can simply replace your loom end plug, plug it into the lighting circuit board and your ready to roll.  More than likely if you are changing the guard you also have a new lighting arrangement and no circuit board. In this case we simply cut the wiring loom down to suit out new lighting arrangement (we were upgrading to a TC Bros choppers '33 Ford side mount tail light kit and small bullet indicators) and installed bullet type connectors so they could be unplugged at a later date if required.
    • Remember to heat shrink all joins to keep the moisture out!

    We hope this has provided some info for those of you out there considering this!  All the best and happy wrenching!

    If you have any specific queries you can hit us up via email