Author Topic: Fire wall burnt wire help  (Read 1576 times)

Offline ChiefSid

  • Newbie
  • Posts: 3
  • Newbie
Fire wall burnt wire help
« on: March 22, 2021, 07:07:42 PM »
I have a new to me 1979 K20. I mistakenly put the positive to negative, negative to positive terminal leads on the battery. A wire on the fire wall wiring block started smoking. I quickly removed the leads but it was too late. A red wire to a plastic covered fuse link? burnt up. I can't get the link apart to replace it (if that is possible). Any help would be appreciated.

Offline Mike81K10

  • Site Supporters
  • Junior Member
  • ******
  • Posts: 878
Re: Fire wall burnt wire help
« Reply #1 on: March 22, 2021, 07:16:56 PM »
You blew the fusible link. Check out this link!
http://forum.73-87chevytrucks.com/smforum/index.php?topic=5748.0
« Last Edit: March 23, 2021, 11:08:15 AM by Mike81K10 »
"Tell me and I forget. Teach me and I remember. Involve me and I learn." -Benjamin Franklin

Offline ChiefSid

  • Newbie
  • Posts: 3
  • Newbie
Re: Fire wall burnt wire help
« Reply #2 on: March 22, 2021, 07:29:11 PM »
Thanks I appreciate it.

Online bd

  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6438
Re: Fire wall burnt wire help
« Reply #3 on: March 22, 2021, 09:42:36 PM »


The fusible link melted because the alternator diodes were momentarily forward biased when the battery cables were reversed, creating a direct short to ground through the alternator.  The fusible link melted protecting the alternator.  The fusible link is the ~6" length of 16-gauge fusible wire that runs between the firewall junction block and the splice with the two 12-gauge red wires.  The polyurethane cylinder enshrouding the three-wire junction just insulates the splice.

Disconnect the battery ground cable.  Cut the two 12-gauge red wires where they exit the splice.  Disconnect the fusible wire from the junction block and discard it.  Procure a 6" length of 16-gauge fusible wire and parallel- or butt-splice it to the two 12-gauge red wires.  If the 12-gauge wire strands are coated in dark reddish-brown tarnish, burnish the wires until they appear bright and shiny.  Crimp then solder the splice using electrical grade 60/40 rosin core solder.  Insulate the splice with marine grade, adhesive lined, dual wall, polyolefin heat shrink, ensuring that the heat shrink extends 3/8" - 1/2" beyond both ends of the splice.  Crimp, solder and shrink-seal a new ring terminal to the free end of the link, then attach it to the junction block.  Reconnect the battery ground cable and you should be good to go.

For supplemental information on fusible links, read Fuses and Circuit Protection and How to make a fusible link.

Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline ChiefSid

  • Newbie
  • Posts: 3
  • Newbie
Re: Fire wall burnt wire help
« Reply #4 on: March 23, 2021, 10:19:54 AM »
Great information
THANK YOU