I recently had the main power fusible link blow out on my 67 Special with a 340/4 V8 and I was surprised that there was very little available on the web on how to replace the old GM fusible link. Maybe it is obvious, but I thought that I would share my experience for others to use. I am no expert, but this is what I did: The Fusible Link (FL) on the older GM cars is on the starter solenoid, which, of course, is attached to the starter. There are two fusible links, one is 14 gage and the other is 16 gage (GA). The 14 GA FL is for all the power on the car except the lights, and the smaller one is for the lights only. See Pictures. The FL is used to protect the circuit by failing before the main wire fails due to an over-current condition, like a fuse. But unlike a fuse or circuit breaker, the FL will take short duration over-current conditions. The FL has heavy insulation also, so that when it fails (melts) it does not melt other wires nearby. So it is a special wire designed to perform like a fuse but much slower. In the picture you can see the larger wires they feed. The main wire from the battery goes to the large stud on the starter to give it power. The FLs come off the same stud so they draw their power from the battery and feed the lights and everything else. The FLs are normally two wire sizes smaller than the wire they are protecting, so the 14 GA wire is attached to a 10 GA wire, and the 16 GA is attached to a 12 GA wire. Note that the FLs share a lug on the factory wiring. The large black lump you see at the connection is a rubber block over a metal crimp used to connect the two different size wires. There is no solder. On my car the main FL melted. I disconnected all the wires from the starter solenoid so I could pull the wiring harness down to work on and to clean all the connectors. I cut the melted FL from the lug and sealed off the remaining wire. I also cut the other end off of the 10 GA wire and cut the insulation back about 1/4”. I used all NAPA parts for the repair. See the pictures. The 14GA FL is NAPA 784696. I attached it to the 10 GA wire using a metal crimp connector similar to what the factory did. The part I used was NAPA 784274. These are unique in that each end is different. One end is for the 14 GA wire and the other fits a 10 GA wire. Nice! I removed the plastic from the metal connector so I could seal the whole connection in heat shrink tubing and I used NAPA 784664. This is also unique in that it is clear and it has an adhesive on the inside to help seal it. If I left the plastic on the connector it was too big for the tubing to go over. Also I found that I could not crimp the connector without breaking the plastic. I used a short piece of smaller heat shrink next to the connector to make the 14 GA FL wire about the same size as the 10 GA wire. This will help to seal the end of the larger clear heat shrink. I crimped the 14 GA FL, slipped the clear heat shrink over the 10 GA wire and crimped it. I used a standard crimping tool (Greenlee KP1022D). I centered the clear heat shrink over the crimp (it overlapped the wire about 1 ½” on each side) and shrunk it. After it cooled I wrapped it in quality electrical tape. Sorry, no pictures as my camera broke – bad day! Before you reconnect everything, find out why it melted. I used a small wire and a 5 amp fuse and hooked the FL up to the battery to see if it would blow/overheat. Turn on everything one at a time and see if there is a circuit that is causing the failure. When you find it, repair it! That’s about it, reassemble everything and away you go!
Instructions on how to diagnose fusible link problems, and repair them is in every Chassis Manual. It's in the Battery and Cables section. Good write up though Bill.
What always irritates me is the blue 14ga butt connector they come with. Useless. Your not getting a 10ga or a 12ga wire in that connector. I did exactly what Bill did and get a package of those very same butt connectors. They're called "step down" butt connectors. And like Bill I removed the yellow plastic and used heat shrink. Great minds think alike.
Nice write up! I do so much electrical work at the shop that 15 years ago I invested in the ratcheting style crimping tool. I use the die that has the "W" shapes 99% of the time as it makes the double folded OEM style crimp (top right die in the attached picture, .... along with the mating bottom right die). I stock most of the common type of terminals which have the secondary strain relief crimp tabs which require that double style crimp, but even when I use the hardware store colored insulated crimp terminals I slice off the vinyl insulator and give it the "W" crimps (lining up the center rib in the die with the split in the terminal). One tip that you guys may or may not know about is when you are making a connection and using shrink tube in an environment that see's moisture I coat the connection with 3M clear silicone sealant, then slide the heat shrink over and give her the heat. Once it cools you clean off the excess silicone and no one will know its there. Larry
Awesome write up Bill so much more detail than what the factory manual provides. I never knew about the step down connectors and love the idea of the silicone within the shrink tube.
Thanks guys! The repair is fairly simple. I mainly wanted to show the repair parts that I found. A couple of notes: On the later cars the wiring harness goes under the engine mount in a rubber block so it may be difficulty to get enough slack to work on. Also, the step down connector makes the job very easy. Many FLs come with a connector already attached that is the same gage as the FL. You have to cut it off and toss it - what a waste!
Fusible link wire is FOUR gauge sizes smaller than the wire it protects--exactly as your examples show. Otherwise, very well done.
