Fusible link question

[Chrispbrown36]

I spent 4 hours in the Tractor Supply parking lot replacing the ignition switch and trying to find a short in my ignition wiring and finally having it towed home. First thing I did was hop on here and everything pointed to the fusible link on the fire wall. I strapped on the headlamp and headed out there. Sure enough the fusible link was melted in half. So my question is....do they just fail from age or should I be looking for some other problem down the line that made the link melt? The truck is an 87 V10. The link appears to be original.

[hatzie]

It failed because you have a short. Whether it's a one time deal is another question.
Circuit 2 is only fused by the fusible links. Grab the 87 & 88 wiring diagrams and start looking at your primary circuit 2 wire termination points then chase it from there.

[aharper33]

Originally Posted by Chrispbrown36

I spent 4 hours in the Tractor Supply parking lot replacing the ignition switch and trying to find a short in my ignition wiring and finally having it towed home. First thing I did was hop on here and everything pointed to the fusible link on the fire wall. I strapped on the headlamp and headed out there. Sure enough the fusible link was melted in half. So my question is....do they just fail from age or should I be looking for some other problem down the line that made the link melt? The truck is an 87 V10. The link appears to be original.

I would say replace the fusible link first and see if it does it again. If it does then you can look for a short somewhere. I would say its the quickest cheapest check. I know the feeling. This happened to me last winter after I had to help jump start a friend of mine. My fusible link looked good so I thought it was something else and I ended up replacing just about every electrical part on my truck it seemed. I replaced my starter, alternator, coil, distributor, ignition box, and replaced just about every wire I could with new wire. Everything worked great for about a week and then the fusible link would pop the fuse just about every time I started my truck. So I replaced it with a new heavier duty link and have not had a problem since.

[Chrispbrown36]

Problem found. The previous owner bragged about how he had put a new starter on the truck just the week before. What he failed to mention was that he hadn't worried much about keeping the wires off of the exhaust manifold. Wonderful mess.

[hatzie]

Originally Posted by Chrispbrown36

Problem found. The previous owner bragged about how he had put a new starter on the truck just the week before. What he failed to mention was that he hadn't worried much about keeping the wires off of the exhaust manifold. Wonderful mess.

Nice when the problems are easy to find. Not so nice cleaning up after a PO. Did he neglect to install the heat shield bolted to the bellhousing bolts too?

Originally Posted by aharper33

I would say replace the fusible link first and see if it does it again. If it does then you can look for a short somewhere. I would say its the quickest cheapest check. I know the feeling. This happened to me last winter after I had to help jump start a friend of mine. My fusible link looked good so I thought it was something else and I ended up replacing just about every electrical part on my truck it seemed. I replaced my starter, alternator, coil, distributor, ignition box, and replaced just about every wire I could with new wire. Everything worked great for about a week and then the fusible link would pop the fuse just about every time I started my truck. So I replaced it with a new heavier duty link and have not had a problem since.

Circuit 2 is 10AWG wire. 10ft of 10AWG wire will carry 50Amps. The fusible link likely blows at 5-10% less than the max current of the wire it protects. 50Amps is a fair amount of juice. That much juice easily will set stuff on fire.

Unless you want an eventual fire... Fix the problem that's causing the fusible link to blow. Don't use a larger gauge fusible link.

If a replacement fusible link of the proper gauge doesnt blow immediately use an infrared thermometer to look for elevated temps in the harness after 15-20 minutes with the engine and normal accessories running. 5-10 degrees hotter than the surrounding wires is a pretty god indicator of where your problem child is living.

[Chrispbrown36]

Originally Posted by hatzie

Nice when the problems are easy to find. Not so nice cleaning up after a PO. Did he neglect to install the heat shield bolted to the bellhousing bolts too?

Apparently so....