Exterior lights/Fuse block

[1978C201964]

I recently bought a 1978 C-20 no factory air and 454 Eng.After rebuilding my 1st carburetor, and removing tanks I found that the electrical system was a nightmare too. My issues are these. 1. Do I install a 7, or eight pin headlight /dimmer switch? 2 . It is my understanding after downloading a schematic from Rick (Thank you btw ).The switch has two positive power feeds. Red for headlight power, and Orange for tail lights. I have no clue how or where the orange feed is hooked to the Fuse block(or does it require an inline fuse before plugging it into the Fuse Block ?). 3. Can anyone share a clear photo of the Factory fuse block as all the writing on mine is illegible. Tape designating what feeds are plugged into the block would be helpful. I spent days avoiding asking for help but after all my research I can not find a clear photo anywhere. Thank you to anyone that can help.

[bd]

Front and rear iillustrations of the fuse box are located in the lower right quadrant of the schematic on page 13 of the 1978 Wiring Manual.  Magnify the view to ~300%.  The 20-amp tail lamp fuse is marked "TAIL LPS  CTSY."

For a simplified diagram and legend of the headlamp switch wiring see Diagnosing dash instrument lights.  Lamp wiring is the same for all years.  Notice that the instrument lamps fuse is in series with (and subordinate to) the tail lamps fuse. 

The seven-wire headlamp switch is standard for 1973-1987(91) C/K/R/V trucks.  However, the eight-wire switch will substitute seamlessly with one terminal left unused and no changes to the wiring.  The headlamp dimmer switch mounts to the floorboard with two screws and is connected through three wires to the headlamp switch, low-beam and high-beam filaments.

What problem are you trying to solve?

[1978C201964]

Well Ty for your time. I can't read a schematic. I don't understand them. I have them all and made reference to looking at them in my 1st message.What I asked for is what I need.A simple picture. I wish I had your understanding of them but I'm at a loss.It seems that every answer I get is going to be" go look at this schematic"If I could read them I would not be here asking for help. Have a great day.       I clearly asked where and how the orange feed attaches to the fuse block. You did answer my switch question( appreciated). I trailered this dead horse home with 0 wires plugged into the interior fuse block. I rebuilt the carb from scratch, my 1st. Removed the tanks(all full of rust with holes ) Replacing one , leaving the other off. I fired the 454up and it ran smooth. No lights so I added a new bypass harness and my switch now works as an on off while batter power is directed to the lights through two firewall mounted relays. So far I have been on my own. Not a mechanic but I research the heck out of everything. 37 people looked at this post and I got one reply, yours.  Referring me to the schematics I already have . Ty for your time but it is very aggravating. How hard would it be for another person with my set up(C-20 1978 , 454  no factory air )take a photo of their fuse block, tape on wires to identify wires plugged into the box ? This id why I tried not to use the forum. Here you either understand the Schematics, or you seem to be on your own still.

[bd]

    No one is born knowing how to interpret a wiring diagram, so NOW is the perfect opportunity to learn!  Or, at least, try.

Can you read a road map?  A wiring diagram is no different. 

• Electrical components (e.g., switches, lamps, fuse boxes, motors, relays, turn flashers, gauge/warning lamp sending units, radio, speakers, etc) are laid out approximately where you will find them in the vehicle and sketched to help identify them for rapid orientation.
  
  
• There is a beginning point and an ending point for every wire.  Every wire is labeled at crucial spots along its length with its gauge, color, and OEM circuit number.  For example, follow the orange colored lines in the lower image to find "18 ORN-40A."  This is the orange wire that connects the headlamp switch to the fuse box "TAIL LPS  CTSY" fuse; 18 is the wire gauge, ORN (orange) is the color of the wire jacket, and 40A is the OEM circuit number to help distinguish it from other orange wires.
  
  
• Wires are drawn along an imaginary grid in straight lines with 90° and 45° bends where necessary to make them easier to follow with your eyes.  The trick to avoiding overwhelm is to follow one line at a time.  When you are first learning, you may find it easier to use a straight edge to follow a particular line.
  
  
• Solid lines represent wires that are part of the wiring harnesses used in all truck models.  Dashed lines represent wires used for optional equipment that may exist only in select vehicles.
  
  
• Where lines intersect they do not make electrical connection unless the intersection is marked with a solid bold dot (see "SPLICE 2" where the multiple "12 RED-2_" lines intersect).
  
  
• It is common for unique wire connectors to be annotated with OEM part numbers, making a schematic diagram appear overly busy.  Practice recognizing them for what they are and ignore them.

The orange wire in question runs directly between the headlamp switch and the backside of the fuse box where it crimps to the "TAIL LPS  CTSY" fuse upper terminal.  It is hardwired and integral with the factory harness and fuse box assembly.  It doesn't "plug in" to the fuse box.  If the circuit is dead, check the fuse terminals for corrosion and make sure the fuse end-caps are not loose on the glass tube.

[1978C201964]

Maybe this will help I did follow the wires, even made up a highlighted schematic of my own showing the outcome of me following it.I was looking for a plug in, you say it is hard wired. There in lied the problem. Someone must have cut the harness and now I need to look for the b section of the wire to finish the equation. Thank you for your time again. Going to go out and pull the fuse block to see the hardwired wire. Be back after i learn something 

[1978C201964]

Turns out I had a few shorts behind the fuse box.Cleaned all Fuse box connections and coated with dialectic grease. Cut/soldered and coated each with dialectic grease and shrink wrap. Made sure to get a hot solder too, just learned soldering today. After I get it all back together I will work on my other part of the dilemma. Trying to understand the light switch. I still don't know how to get the harness to power the tail lights part of the headlight switch. Thank you again, can't believe I got this far. Learning soldering was fun.

[1978C201964]

There was a wire nut holding a splice about mid way on wire 18 ORN-40 A. Would my connector at the light switch get soldered to that splice after separating it ?

[1978C201964]

The wire went straight from the fuse box to the courtesy light. They bypassed the switch completely, and wire nutted it together. Would it be correct now that I have corrected all the burnt wires near the fuse box to separate that wire at the wire nut and add my light switch into the circuit ?

[bd]

The wire went straight from the fuse box to the courtesy light. They bypassed the switch completely, and wire nutted it together. Would it be correct now that I have corrected all the burnt wires near the fuse box to separate that wire at the wire nut and add my light switch into the circuit ?

You can do that but replace the wire nut with a proper crimped and soldered inline splice insulated with marine grade heat shrink.

[1978C201964]

Placed a quick disconnect on the b- side in case I screwed up badly. Turned the key and tested all the lights. IT LIVES!!!!!!!  .. Thank you for your patience. As much as I would love to leave you alone , you have proved yourself INVALUABLE!!. Sorry to say I will be back with more problems until I get this truck right.