99ford

first, sorry for posting in the wrong section. second, what is the bulkhead? thanks for your help

been searching for days just need some help on where the VSS is for a 1999 ford f150 lariat ext. cab. pictures would be great, but a good explaination is fine. I tried installing it without the wire connected but it seemed to lag on the screen a bit. thanks guys for your help ahead of time.