2002 Other Oldsmobile Models Connecting trailer lighting dis

I am attempting to complete the installation of the trailing wiring. The van came with a factory provided wiring harness "pigtail." I have used bullet connectors to attach the harness to on of two different Hoppy convertor assemblies. The first was the correct converter (as confirmed by Hopkins Mfg tech support) to combine separate turn signal with the brake lights in a flat 4-wire lead. The second was a power tail light converter (separate fused lead to battery and separate ground wire -- provided at no charge to me by Hopkins -- to resolve the following problem. (Neither has corrected it.)

Problem -- when any one of several trailers with flat 4-wire leads is connected to the vehicle and the vehicle is started the trailer lights fail to operate properly and the TCS disabled and ABS warning messages and lamps are activated.

The one variable I have not yet tried is to eliminate the OEM trailer lighting pigtail and splice directly into individual lamp wires. I'd prefer not to do this unless absolutely necessary as the OEM connection is much more convenient.

Any suggestions for troubleshooting and fixing this problem.