Background
If you are using the LS series of engines, the Electronic Throttle Control (ETC) is the module that has a throttle pedal attached to it, and signals the engine computer that the pedal is being depressed, and by how much. The engine computer then calculates the correct amount of air, fuel and spark to achieve optimum engine performance.
The Problem
The problem is that in our mid-engined cars, the throttle pedal is often placed too far away from the controller to use an un-modified harness as delivered in the popular GM controller kits (which typically include the engine computer, the ETC and the rest of the harness, along with other key parts).
Some builders unwrap enough of the harness and find sufficient length to reach the ETC connector on the throttle pedal. Others have mounted the ETC in such a way that an extension really is required. In any case, if you decide you need a longer cable, this note is for you.
Some solutions
Some people just cut and splice the harness, though the GM controller instructions explicitly prohibit this. Apparently, if done carefully, this can work. (See the note below.)
Another alternative is to obtain an extender harness that plugs into the existing harness and ETC to effectively lengthen the harness in this critical area.
Extender harnesses can be obtained from Current Performance, Caspers Electronics, or from other sources of custom harnesses. The author obtained a 4 ft extension cable from Current Performance for around $30. You may have to ask for the harness as it isn't listed on their website. Current says they do this all the time with good results, and that it is common practice on sandrails, for example.
Whatever solution you choose, it makes sense to measure the overall harness resistance before and after the change. If EACH wire has the same resistance as before, you are good to go.
NOTE: If the resistance of the total harness from the ETC to the engine computer (ECM) is different, the ECM may never see full throttle opening, for example, and full power may never be achieved, or driveability problems may occur. Some differences in resistance may be able to be accounted for with sophiticated tools like HP Tuners- check with your tuner to be sure before you make your own changes.
Here is a picture of an extension harness: