Have you replaced the HG prior to this leak starting? There are only a couple places for oil to leak and enter the timing belt cover: Main bearing seal, Oil pump drive seal, Cam seal (x2), Head/Block union (where you're supposed to put the packing before you put the HG on).
It this a GE or a GTE? The only additional wires for the Cali EGR system are Black with a yellow stripe and Brown... It comes off of the harness as it runs along the firewall.
If you were to give locations or post photos it would be easier for people to help. No one is going to read through the entire TEWD to see if they can track it down just based on color.
If they're on the engine harness you may have luck skimming the following pages... if you don't find it don't be surprised, the online TEWD is for a '91.
GTE
http://www.cygnusx1.net/Supra/Librar...px?S=Main&P=46
GE
http://www.cygnusx1.net/Supra/Librar...px?S=Main&P=54