Harness connections -note some will not apply to your harness

Before beginning please be sure you have a proper engine to battery ground, if you do not their is a chance the engine harness may be damaged when starter is en-gauged due to the harness acting like a ground strap and over loading the small engine grounds in harness and melting/burning harness.    

The battery lead needs to be connected to the battery + terminal, also an easy solution to tucked battery locations would be to attach the harness to the starter battery + post as you should already have a nice large battery lead running to the starter-and the leads are long enough to reach the starter on most every harness.

Fuel pump + needs to power up your fuel pump.  Simply unhook the oem wires/cover the ends for safety, and extend new lead to the fuel pump(s) - some cabbies have lift pumps so be sure to power both pumps!!!

Body ground needs to simply be attached to a clean metal surface on car with a nut/bolt or self tapper screw.

The trigger lead is the most difficult lead for most.  it needs to be attached to a power source that is 12V when the key is turned to on position AND stay 12v while the key is in crank position.  A sure fire method is to attach to the smaller black wire on most all mk1-mk3 ignition switches.  Its easy to test to make sure the lead is good, just hook a test light to the suspected trigger lead you want to use.  Turn the ignition key on- light should glow. Now turn the key to start/crank and the  light needs to keep glowing....if it goes out it will not work and find another.  if all else fails a small toggle switch from the battery plus to the trigger lead will work-switch on will make ecu alive, switch  off would shut off motor.

The coolant gauge lead uses the factory sender and hooks to the oem lead in your cluster harness to make the gauge read, in some cases it may be incorrect so verify operating temps on gauge using a scan tool and compare ecu coolant temp to actual gauge.  Resistors can be added to lead to bring reading down on gauge as some mkiv senders read "high" on older clusters.

The oil pressure light is a simple dummy light circuit.  The lead is grounded when engine is off, and goes open circuit when engine starts.....on a mkiv the sender is reverse function.  neither are actual gauge leads, just for dummy light.

The oem tac lead will need a signal booster for older mk1/mk2 clusters and can be supplied when applicable.  On mkii and up clusters the oem tac lead generally will work proper.  On vr6 with 4 cyl cluster a full tac adaptor must be used and can be supplied when applicable.

Glow plug light is a ground switch supplied by ecu for cluster function of glow plug bulb.

Two step lead if present will be a twisted loop at the ecu connector. When this wire is cut and “not connected to itself” and the throttle is depressed beyond 80% two step will bang and pop- use at your engine/exhaust own risk- not responsible for any damage resulting from “explosions”!!

For no start conditions first things to check:

Verify the ecu will communicate with a scan tool, note that obd1 ecu’s will ONLY work on a VCDS scanner.

With obd1 ecu’s the fuel pump should prime for 1 second when key is first turned on, if it does not their is a very good chance the ecu is bad….very common on obd1.

On odb2 ecus the fuel pump will only prime once and then not again for some time with key cycles, this is normal.

Check for spark while cranking, if you have no spark, that’s not good…..next check to see ecu understands the motor is rotating.  To do this have a friend help or use a test light.  First method is to pull the fuel line feed, put it in a bottle and crank motor, fuel pump should fire up while your cranking the motor over….if it does the ecu is seeing engine rotation, this is good.  Second method is put the test light on the fuel pump + lead and make sure the light glows while cranking.

Next temporarily run the trigger to the battery plus and retest above steps, if anything changes then you need to find a proper trigger lead power source as stated in above description of trigger lead.

Next if its OBD2 you should hear the throttle body hum with key on, this means ecu is alive!