Parking Light Circuit Issue. Helppppp!!!!

[Irv Reed]

I have an 86 mustang with complete 90 swap. Air bag dash w 140mph speedo, mass air, everything is swapped. When I turn on the headlights the dash goes crazy, tach drops, temp spikes, turn signal indicators light up. If I take the brown wire out of the headlight switch it doesn't mess up. That means the dash lights or running lights are causing it. I've run grounds EVERYwhere it seems. Can't find a diagram for just the running light circuit. Key off, headlights on with brown wire in, dome light switch causes fuel pump to prime. Please help me before I light it on fire!!!

 

[TuneUpsNSuch]

Step one. Get connector pinout for '90 IP and compare with connector pinout for '86 IP.

 

[Irv Reed]

It has the whole 1990 harness it seems. All the pinouts match up to the 1990