Blown Fusible link

[Kaleb555]

Hi I'm new to this forum and need some urgent help. I recently replaced the starter on my 79' k10, and hooked everything up correctly until I got to my battery. I was blinded by the fact I was about to finally have my truck running that I hooked the terminals up backwards. I went inside to start the truck, then saw a steady stream of smoke coming from the starter location and at the terminal junction on the firewall. Now my starter won't even click. My other electronics work like wipers and lights but no starter. I was wondering if I blew my fusible links or if it's something else. Any info will help THANKS!

 

[RThiel]

I would agree that it's the fusible link. That's the weakest point of the wiring.

 

[VAL]

Agreed! It happened to me once, I fried the link on the firewall by the master cylinder.

 

[chengny]

The reverse current condition probably blew the diodes - that are used in the voltage regulator section of the alternator. So, unless you are up for changing the VR, there is a good chance that you'll be in the market for a new alternator. That's the bad news.

The good news is;

1. From what you describe, it appears that the fusible link(s) functioned exactly as designed. When the current flowing through them exceeded the maximum rating of the associated wiring - they melted. With any luck, they did this quickly enough to prevent any damage to your wiring harness.

2. Other than the VR diodes noted above, there are virtually no true "electronic" devices in a 1979 GM truck - just simple electrical components which are generally not affected by reverse current conditions.

There are two main feeds that supply the truck's electrical system.

The main feed that you currently have no power available from is protected by two fusible links. There is one down by the solenoid end and another that you saw at the firewall junction block.

 

[Kaleb555]

thanks for the replies! Glad its something simple. do any of you know where i could buy the correct fusible links? ive been to a couple autoparts stores but none of them carried any that looked like mine.

 

[RThiel]

They literally are a chunk of wire that you splice on to the end. Nothing special. I guess if you're concerned about it being "correct", I usually have good luck with rockauto.com.

 

[chengny]

A quick check found these are available at PB's, OR's, Napa & ADV:

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

Look closely at your links and you will see 2 digit number on the plastic collar (e.g. 14,16,18). That is the AWG size of the copper conductors inside the insulation. I am almost positive the one connected to the firewall JB is a 16 AWG wire. So, assuming I am remembering right and reading this picture correctly:

You must be registered for see images attach

and it is a 16 AWG link, we can also figure out the sizes of the links located at the solenoid by consulting the wiring diagram.

But look, somebody already did it for us:

You must be registered for see images attach

I found that on another Chevy truck thread that I know and trust, so you can feel confident that the link sizes are correct. BTW - below is the thread's original post. You should read it:

I have a 1980 k10 silverado that I put a new 350 in and got all the electrical hooked up and went to hook the battery up and was in a hurry to get the truck started and hooked the battery up backwards. I put negative cable on postive bat post and pos cable on neg post. When I did that up on the firewall above the driver side valve cover something smoked. I have looked on here and got an idea that it might be a terminal block? Is that correct? So what I did is got the battery hooked up right and the truck didnt start not even any lights in the dash. What could be the problem? Someone told me to check fusable links and if not that check what smoked on the firewall which i believe might be termianl block. I am not very good with automotive electrical so thought I would get answers from people on here. Hope someone can help me.


Back to me.

A fusible link is just an undersized length of wire with special insulation that is designed to puff up as an indication the copper conductors inside it have burned. Read on for more info on fusible links:


In addition to circuit breakers and fuses, some circuits use fusible links to protect the wiring. Like fuses, fusible links are "one-time" protection devices that will melt and create an open circuit.

Not all fusible link open circuits can be detected by observation. A blown link often, but not always, has "bubbly" appearing insulation making troubleshooting easier. Always inspect that there is battery voltage past the fusible link to verify continuity.

Fusible links are used instead of a fuse in wiring circuits that are not normally fused, such as the ignition circuit. For AWG sizes (wire gauges), each fusible link is four wire gauge sizes smaller than the wire it is designed to protect. For example: to protect a 10 gauge wire, use a 14 gauge link (or for metric, to protect a 5mm wire, use a 2mm link). Links are marked on the insulation with wire-gauge size because the heavy insulation makes the link appear to be a heavier gauge than it actually is. The same wire size fusible link must be used when replacing a blown fusible link.

Good and damaged fusible links:

You must be registered for see images attach

Double wire feed fusible link repair:

You must be registered for see images attach

Choose the shortest length that is available. A fusible link should NEVER be longer than nine inches. Fusible links longer than this will not provide sufficient overload protection.

To replace a damaged fusible link, cut it off beyond the splice. Replace with a repair link. When connecting the repair link, strip the wire and use staking-type pliers to crimp the splice securely in two places. To replace a damaged fusible link which feeds two harness wires, cut them both off beyond the splice. Use two repair links, one spliced to each wire harness.

 

[Kaleb555]

A quick check found these are available at PB's, OR's, Napa & ADV:

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

You must be registered for see images attach

Look closely at your links and you will see 2 digit number on the plastic collar (e.g. 14,16,18). That is the AWG size of the copper conductors inside the insulation. I am almost positive the one connected to the firewall JB is a 16 AWG wire. So, assuming I am remembering right and reading this picture correctly:

You must be registered for see images attach

and it is a 16 AWG link, we can also figure out the sizes of the links located at the solenoid by consulting the wiring diagram.

But look, somebody already did it for us:

You must be registered for see images attach

I found that on another Chevy truck thread that I know and trust, so you can feel confident that the link sizes are correct. BTW - below is the thread's original post. You should read it:

I have a 1980 k10 silverado that I put a new 350 in and got all the electrical hooked up and went to hook the battery up and was in a hurry to get the truck started and hooked the battery up backwards. I put negative cable on postive bat post and pos cable on neg post. When I did that up on the firewall above the driver side valve cover something smoked. I have looked on here and got an idea that it might be a terminal block? Is that correct? So what I did is got the battery hooked up right and the truck didnt start not even any lights in the dash. What could be the problem? Someone told me to check fusable links and if not that check what smoked on the firewall which i believe might be termianl block. I am not very good with automotive electrical so thought I would get answers from people on here. Hope someone can help me.


Back to me.

A fusible link is just an undersized length of wire with special insulation that is designed to puff up as an indication the copper conductors inside it have burned. Read on for more info on fusible links:


In addition to circuit breakers and fuses, some circuits use fusible links to protect the wiring. Like fuses, fusible links are "one-time" protection devices that will melt and create an open circuit.

Not all fusible link open circuits can be detected by observation. A blown link often, but not always, has "bubbly" appearing insulation making troubleshooting easier. Always inspect that there is battery voltage past the fusible link to verify continuity.

Fusible links are used instead of a fuse in wiring circuits that are not normally fused, such as the ignition circuit. For AWG sizes (wire gauges), each fusible link is four wire gauge sizes smaller than the wire it is designed to protect. For example: to protect a 10 gauge wire, use a 14 gauge link (or for metric, to protect a 5mm wire, use a 2mm link). Links are marked on the insulation with wire-gauge size because the heavy insulation makes the link appear to be a heavier gauge than it actually is. The same wire size fusible link must be used when replacing a blown fusible link.

Good and damaged fusible links:

You must be registered for see images attach

Double wire feed fusible link repair:

You must be registered for see images attach

Choose the shortest length that is available. A fusible link should NEVER be longer than nine inches. Fusible links longer than this will not provide sufficient overload protection.

To replace a damaged fusible link, cut it off beyond the splice. Replace with a repair link. When connecting the repair link, strip the wire and use staking-type pliers to crimp the splice securely in two places. To replace a damaged fusible link which feeds two harness wires, cut them both off beyond the splice. Use two repair links, one spliced to each wire harness.

Ok so i replaced the link with two new ones for each harness. but still nothing. i know its not the fusible links at the starter because the starter is still getting power, but only from one cable ( the one with the two fusible links) but not the other wire that goes to the junction block. i tested both the links at the junction block and they both have power. am i doing something wrong?

 

[Kaleb555]

I seems like theres something wrong with the wire going from the junction block to the starter because theres power at one end of the wire but not the other.

 

[Jrgunn5150]

I seems like theres something wrong with the wire going from the junction block to the starter because theres power at one end of the wire but not the other.

Quick and dirty way would be to run a jumper from the terminal down to the starter, if it works, then replace that wire properly.

 

[Kaleb555]

Quick and dirty way would be to run a jumper from the terminal down to the starter, if it works, then replace that wire properly.

from the terminal block?

 

[Jrgunn5150]

from the terminal block?

Yep, alligator clip it or whatever.

 

[Kaleb555]

Yep, alligator clip it or whatever.

which post would i attatch it to on the solonoid?

 

[Jrgunn5150]

Terminal S

 

[Kaleb555]

Terminal S

so when i attatch them just turn the key?