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Home arrow TRE arrow TRE Transistor (Smart TRE)

TRE Transistor (Smart TRE) Print

This page is about another homemade semi active TRE using a transistor to do the switching.

If your model has a factory fitted gear position indicator, it will always read 5th or 6th gear (depending on the resistor used) if you fit a TRE. It'll only work if you have a working neutral light too. I haven't tested it on a cluster that uses a LED for a neutral light.

I had this circuit designed and the information up on the internet long before any commerical manufacturers were offering "Smart TRE's" I first put up this design in Novemeber 2003. Feel confident that this TRE design is as good as any out there. It does what their's does, actually it was doing it 1st :)

TRE Modification

Features and operation

This TRE is semi active like the relay one I built. This means it will not affect the neutral map, but all gears are remapped to either 5th or 6th selected by the resistor value chosen when it is assembled. I didn't include a switch in this one, but it is an easy addition if it's really wanted. I've never had the need to switch my SATRE off, so I haven't bothered with one on this version. Plus the main reason for working on this transistorised version is that it is a simple 3 wire design that doesn't need any extra cables except the ones that run from the GPS - ECU plugs.

The operation is fairly simple. When the bike is in neutral and the neutral indicator is on, the base of the transistor is tied to ground so the transistor is off. When it is off it is seen as an open circuit by the ECU. The GPS signal to the ECU is open when in neutral when the wiring is stock. So all is good.

When the bike is in any gear (not in neutral) there is an effective +12V on the neutral indicator wire (as long as the globe is not blown). This +12V using miniscule current can saturate / turn on the transistor. When the transistor is on, it ties the ECU GPS cable to ground via a 15K ohm resistor which is exactly what happens in 6th gear when the wiring is stock.


  • 3 wire design.
  • No moving parts.
  • Doesn't affect the neutral map.
  • Idle speed is not affected.
  • Doesn't affect starting the bike.
  • No need to remember if it is off or on.


  • The neutral indicator must be fitted and working.

Building and installing of my TRE

Luckily for me all of these things I needed I had lying around the garage. To go and buy these from the local Radioshack shouldn't set you back more than a few dollars. You'll only need some basic tools. Some solder and a soldering iron might be the only items some might not have.


  • 1 X BC549 NPN transistor or equivalent (2222a, there are plenty that can be used)
  • 1 X 15K ohm resistor (for 6th gear) Or 6.8K ohm resistor (for 5th gear)
  • 1 X 47K ohm resistor
  • 1 X Project box or tube to put the lot in
  • 1 Project bread board cut down to suit the enclosure
  • Off cuts of wire and cable etc. I used and old joystick lead to run from the GPS plug to the TRE


  • Pliers
  • Knife
  • Cable Strippers
  • Screwdrivers
  • Soldering iron and solder


Testing that the unit is working is pretty straight forward. Use a high impedance digital multimeter set on volts DC. On the Pink / Red wire that goes to the ECU you should get the following readings to +5V

  • In neutral, close to 5.08VDC
  • In all gears using a 15K resistor, close to 4.70VDC
  • In all gears using a 6.8K resistor, close to 4.38VDC
Or when testing to ground / frame / black / white trace wire you should see the following voltages.
  • In neutral, close to 5.08VDC
  • In all gears using a 15K resistor, close to 0.313VDC
  • In all gears using a 6.8K resistor, close to 0.643VDC

Circuit Diagrams

Here are some circuit diagrams.

The standard GPS & Transistorised set-up drawings.

Simple plug drawings

Here's how you would connect it to the wiring loom. The drawing on the left is simply splicing it into the existing loom. The one on the right is how you would connect it if you got hold of a set of OEM plugs. You can substitute the resistance value for a value of any gear you like (Busa's and GSXR1000 owners would want 6.8K for 5th gear to defeat their speed limiters) but for my TLS, 6th gear is just fine.

Here's a nice PDF of the transistorised TRE created by Glenn Cauley, a member on
Right click "save as".

Transistor orientation

I've had a few questions asked of me about transistor leg orientation. Here's a good site for information Transistor basics Just in case the page disappears I borrowed the following animations from it.

transistor   transistor   transistor

Commercial Manufacturers

Now I've put this information out in the public domain I wonder how long until we'll see this design in production and being sold around the globe as overpriced automatic de-restrictors /TRE's. How long until these start appearing on EBay sold as who knows under what marketing names and claims. This design appeared online November 2003 and I haven't seen any available yet.

If you use or copy this design for a TRE that is a 3 wire design that doesn't affect the neutral running of the bike and automatically switches when in gear all I ask is that you shoot me an email and hook me up with a handfull of OEM connectors and pins and sell them to me for what they cost you. Just so I can make a few up for my FI Suzuki riding friends.

Fat lot of good that paragraph did me. Smart TRE's are everywhere now.


Special thanks to etbadger who was a member on the old TLPlanet for planting the seed and sharing his version of it with me.


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