Ok here is a very quick guide on how to bypass the microswitch trigger on your Heng Long/ Taigen bb or recoil unit. This microswitch triggers the actual firing procedure on the Taigen/Heng Long MFU's. The problems is that this switch does not close as soon as you go to fire using the hand controller. Instead the recoil/bb unit must recoil backwards eventually tripping the microswitch, closing the contacts and initiating the fire procedure. If you wish to have any sort of realistic recoil you must do away with this microswitch and replace it with a switch that operates as soon as you activate fire.
Here is how to do this using a simple 5 volt relay
Step 1
Grab your 8 pin cable
![Image](http://farm6.staticflickr.com/5537/11520771754_da86f95a9f_z_d.jpg)
Step 2
Remove the middle two wires by using a fine point to gently press down on the locking tab and carefully puling out the wire.
![Image](http://farm8.staticflickr.com/7327/11520872643_146e6487f4_z_d.jpg)
Step 3
Solder two short lengths of wire - one (red) piece to the yellow cable and the other (black) to the brown cable
![Image](http://farm3.staticflickr.com/2864/11520793764_ff2b1d38d8_z_d.jpg)
Step 4
Reinsert back into plug
![Image](http://farm4.staticflickr.com/3830/11520857636_d5a4651ffa_z_d.jpg)
Step 5
Solder these wires to the relay coil contacts. NOTE some relays are polarity sensitive so LOOK at your relays datasheet. Yellow/Red is V+ and Brown/Black is V0.
![Image](http://farm8.staticflickr.com/7438/11520786935_06fe870cd7_z_d.jpg)
Step 6
Get two more lengths of wire and solder these to the NORMALLY OPEN contacts of your relay. Unless you have a supply of JST crimps and plugs use an already made up 2 pin cable as shown in Step 7.
![Image](http://farm8.staticflickr.com/7451/11520808254_bd48650c55_z_d.jpg)
Step 7
Your assembly should now look like this.
![Image](http://farm6.staticflickr.com/5497/11520763365_68700c9491_z_d.jpg)
Step 8
Connect to your RX18 or Taigen 2.4gHz MFU and mod is complete
![Image](http://farm4.staticflickr.com/3830/11520866133_03ee678e7a_z_d.jpg)
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