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  • Where does the single red wire in the relay and fuse block center go?
    This is what 'powers up' the PCM. Its important that this key hot power, along with power to injectors, coils, and so on, STAY HOT when cranking over the engine. Some accessory positions on key switches ARE NOT HOT when cranking. This also includes older vehicles that had POINTS ignition. Even the COIL wire on some of those went dead when cranking. This is because when cranking the coil was boosted to 12v+ through the R terminal on the starter solenoid. After cranking, power was restored to the coil through a resistor
  • Where can I install my coolant temperature gauge sender?
    The aftermarket temperature gauge sender can be installed in the passenger side head. An adpater will be required because LS engine threads are metric and most aftermarket temperature senders are US threads.
  • How do I wire my speedometer up?
    Connect the black thats coiled within the "under dash" wires to the speedometer. NOTE: DO NOT tap into the VSS signal of the harness. This will cause the transmission to shift improperly.
  • What is the TCC brake wire for?
    For automatics with lock up converter, the PCM needs signal when brake pedal is pressed. However, the signal needed is opposite how you're brake lights work. The PCM wants 12v+ constant on this wire when brake IS NOT pressed, and OPEN Circuit when the brake IS pressed. If you vehicle was equipped with a lockup trans to begin with, you probably already have the proper normally closed switch mounted by your brake light switch. If you do not, you can use a relay to perform the same thing. On most relays, there are 5 terminals, 2 of them turn the relay ON when provided ground/power. There are then a normally open leg and a normally closed leg on the relay and a supply. By feeding 12v+ on the supply leg, and hooking the Brake Switch Signal wire to the normally closed leg, you will now have the correct signal for the PCM. When the brake is pressed, 12v+ flows to brake lights, tap into this wire, and run it to the relay to turn the relay on. This will cause the normally closed leg to become open, thus turning OFF the 12v+ signal to the PCM. When you release the brake pedal, the relay will turn OFF, and then feed 12v+ to the PCM.
  • How do I get my tachometer to work?
    Vortec 4.8/5.3/6.0 this comes from the PCM, which generates this signal for a aftermarket tachometer. The stock LS tach signal is 4 cylinder type signal. This can be programmed as 4, 6, or 8 cylinder signal. Some 2003+ LS PCM's tach signal is not strong enough, and needs boosted. Please see diagram in the provided instructions.
  • Does all the grounds need to be connected to a ground source?
    All of the grounds within the harness should be connected to a good ground source before attempting to crank the motor.
  • Do I need to plug in the VSS connector if I am using a 350/400/manual transmission?
    You do not have to use the VSS plug, however it is recommended because sometimes if the PCM will not be able to determine how fast the vehicle is going. As a result, under immediate stopping conditions the motor could stall. This condition can be corrected by installing a VSS or through tuning once the install is complete.
  • How do I wire up my fuel pump?
    Since you need the fuel pump back by the tank and at the same level as the fuel or lower, that usually means you're going to have a long run of wire. So, you need to have really good wiring going back to it. Wiring that will carry enough current. Running the current through your ignition switch isn't a good idea since it's probably already overloaded, and will kill the voltage. That will kill the pump. However, it's nice for convenience. That's why a relay is really good to use. It lets the ignition switch activate the pump, while keeping the power from having to run through it. It will keep your pump alive and happy because it is getting full voltage. A good way is to mount a relay beside a power distribution block on the firewall (see Improved Power Circuit) and get the power from there.
  • If using a 350/400 transmission where do I get vacuum for the vacuum modulator?
    The LS intake manifold has a vacuum port available that is plugged from the factory. You will have to snap off the plug and plug in the vacuum hose for the vacuum modulator on the TH400 or TH3350.
  • Do you make harnesses for any other engines?
    We only support GM LSx. We do not support any other types of engines.
  • Do you make a harness for my specific vehicle?
    No. All of our harnesses are "standalone" meaning they are not vehicle specific. We provide speedo and tach output wires from the ECM and is up to the end user to cross them over into their vehicle's gauge setup for functionality. There are only 3 wires you need to hook up to make your LS swap come to life with a Lab Rats Performance harness - battery, ignition switch, and fuel pump! We make it as simple as possible, and all of our wires are labeled for easy hook up.
  • What is Drive-By-Wire (DBW)?
    The typical throttle body that had a braided cable attached to the gas pedal for acceleration changed in 2003 on the vortec/truck motors. The 2003 vortec/truck motors throttle body blade is controlled by an electric motor. The gas pedal is basically an sensor that sends a signal to the TAC (throttle actuator control) module. The TAC module and the PCM work together for control of the throttle blade within the throttle body. If you buy a vortec/truck motor from a 2003 and up, make sure you get the Gas Pedal Assembly, PCM and the TAC module (throttle actuator control). Those three items are needed for a successful LS SWAP.


Lab Rats Peformance, LLC specializes in the design and manufacture of Standalone Wiring Harnesses for GM Gen II, III, and IV LS based engines and transmissions. These harnesses include the Gen II LT1/LT4, Gen III (24x) LS1/LS6 and Vortec Truck Engines as well as Gen IV (58x) LS2, LS3 and LS7 Engines. In addition to wiring harnesses, you will find other components and kits for retrofitting older vehicles with these powertrains including PCM programming, Fuel Pump Kits, Engine Sensors, Extension Harnesses, Replacement GM connector pigtails and a complete line of hardware to complete your conversion needs!




PHONE: 504.603.0249

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