1988, E150, 5.0. If it makes any difference, it rolled off the line in 10/1987.

I found these wires like this when looking around the van.. Two are blacks and the other is brown/w blue stripe. They were already twisted together and with no wire connector.. The brown/w blue stripe is hanging on by one strand.. The dimmer has the standard 3 wire connector.. They are part of the factory harness..
Thanks.

 

Dont ask me why yet,, but I believe those wires have something to do with the door switches and interior dome light... After searching quite a while for 88 e150 dome lite brown with blue stripe, I came across an article about overriding delay light switch on an f150 and it mentioned the brown/w blue stripe wire. My dome lights do not work..

 

The buzzer does come on if the drivers door is open and the key is in the switch

 

Ok after much research and very little turned up.. One Ford wire color chart says the brown with blue stripe is for the door switches.. Several posts say it is for the seat belt latch switch.. since it has conversion seats and I have not seen a seat belt light or heard a seat belt buzzer, I assume the conversion company disconnected it and the wire nut has fallen off over the years..
I also traced the brown /w blue stripe wire to the door/key buzzer...

 

Is there a ground point somewhere that doesn't have its wires attached? That's what I would guess without seeing the rest of it.

 

My 85 e150 is not here t my house right now but I am going to look at it and see what is down there as it too is made by the same conversion company... I think it goes to the seat belt

interesting from Ford-Trucks there is a post about a 2005 truck that says
brown with light blue stripe -------Seatbelt buckle switch

and from a 2004 super duty f series camper it says
Warning Chime — Seat Belt Brown-Lt. Blue Stripe Top Side of Dash Panel (Part of 14A318-A w/Asy) —

In my searching I did come across an interesting set of wiring diagrams that might help someone out, I will post in the main forum.
It's called
Body Builders Layout Book
ELECTRICAL WIRING
GENERAL PRACTICES
ADDITION OF LIGHTS OR ELECTRICAL DEVICES

Its for 2014 models though

 

Just thought I would ask since most of the darker wires are generally grounds of some sort. Is there anything that seems out of the ordinary? If nothing seems to be wrong with any of the operation then maybe you could just put a wire nut on it to protect it.