Making a communications (USB) cable

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Ignitron ECU connects to your computer via USB. Since USB is available on almost all PC-s and notebooks (even on some tablets) it is a straightforward choice, but USB was not primarily designed for use in such a harsh environment. If any of the conductors (including the shielding) in the communications cable gets damaged or deteriorates, the connection to your ECU will be unstable!

The main reason for cable damage is mechanical strain, for example: pulling the cable through the firewall with excessive force, sharp turns/twists, closing the glove box door on the cable, etc... Most of the times it is not the cable itself causing the problem, but the connector at the notebook side (sometimes chopping off and installing a new notebook side plug from an other cable can help). If the USB plug is loose and no adequate connection is made between all contacts (including shielding) the connection can be intermittent!

DO NOT upload files (do not ever upgrade firmware) to your ECU with an intermittent connection!

Damaged communications cables are not covered under warranty, but can be easily prepared using generic USB 2.0 printer cable or any USB cable which is long enough for your needs and has a USB Type-A male connector on one end. Do not use a cable which is too thin (f.eg less than ~4mm in diameter) also it is not suggested to go longer than 3 meters! A generic USB 2.0 cable contains 4 conductors under a shielding. The shielding can be foil type or a braided or both. Chop off the connector from the other end and remove outer insulation including shielding to reveal conductors. Make sure to locate the drain wire, do not cut it off (it is often buried in the braid)! The drain wire will be needed to connect to the shielding.


Ground (black), +5V (red), DATA- (white), DATA+ (green) and DRAIN wire for shielding.

There are two versions of the Ignitron ECU available with different communications connector at the back. The old connector can be reused off your old communications cable as it rarely gets damaged, but you can buy new if you would like to (see part numbers below).

9 pin waterproof DSUB version

If you have the 9 pin waterproof DSUB type plug at the ECU end, you can reuse your old one or get the "Amphenol SDB-09BMMA-SL7001" or equivalent. Non waterproof DSUB9 connectors can also be used, but they are not suggested!


ECU pinout for communications cable at the back
Pin 1: Ground (black) + shielding (drain wire)
Pin 2: +5V (red)
Pin 3: DATA- (white)
Pin 4: DATA+ (green)
Pin 5-9: reserved

Be sure to connect the ground (black) wire and the drain wire (shielding) together! Solder the appropriate wires to the connector according to the pinout! Do not connect anything to pins 5-9, leave them unconnected!


Example for soldering. Drain wire and ground (black) are connected together!

4 pin circular plug version

If you have the 4 pin circular plug at the ECU end, you can reuse your old one or get a "TE T4112001041-000".


ECU pinout for communications cable at the back
Pin 1: +5V (red)
Pin 2: Ground (black) + shielding (drain wire)
Pin 3: DATA- (white)
Pin 4: DATA+ (green)

Be sure to connect the ground (black) wire and the drain wire (shielding) together! This plug has screw terminals, no soldering needed. We use ferrule crimping on the wires before installing them into the sockets. Secure the appropriate wires to the connector according to the pinout!


Example. Drain wire and ground (black) are connected together!

Testing the resistance of conductors

You should test the resistance of every conductor in your communications cable with a multimeter! This should be done before assembling the plug housing, as it is easier to access the terminals this way. If the plug is already assembled, find a suitable needle or pin to reach the terminals inside the plug. All power and data lines (4 hard to reach contacts inside the USB Type-A male plug) should have a resistance less than 5 ohms (end to end), preferably closer to or below 1 ohm. The shielding (outer metal housing of the USB Type-A male plug) can have a higher resistance, but not more than 20 ohms! If your cable has higher resistances than these numbers and you experience connection problems to the ECU then you should replace the USB lead!