I recently ordered a replacement engine wiring harness for my Cutlass Supreme. The plug is behind the brake booster and difficult to access easily. It appears to be held on with clips. What advice does anyone that has replaced this harness to avoid damaging the connector on the firewall? Thanks!!!

 

I can't remember if mine had a screw in the center of the connector?

 

There is a bolt in the center that hold the harness plug to the fuse box. I don’t think the bolt will come out of the connector.

Use a heat gun on low heat to melt the gooey grease GM used to seal the connector from the weather. A little heat and some gentle wiggling and pulling should be all it takes to separate the 2 parts.

 

No screw on the 66/67 bulkhead connector , just lots of sealer and one top and bottom clip.
Only way I have been able to do is using my left hand, clean as much of the sealer off so the clips will move, pull up on the bottom one and a little out on the harness connector , then while holding a slight tension on the harness use your thumb to push down on the top clip and work the connector off. it's not much fun and in my case much cussing was done.
the new harness should come with grease in side the connector , make sore it is not over greased as I had trouble getting mine to lock in because it had to much.
the first pictures show the sealer and the second is of a cleaned bulkhead.