Fusible link issues.

[Jrparadis]

Hey Everyone,

I have a 78 C10 that I am trying to get back on the road and the wiring is an adventure. I blew up the original 454 and am trying to finish hooking up a replacement. Today when I tried to bump the starter a big puff of smoke appeared.

So I know this is the fusible link getting destroyed and I’ll need to replace it but my questions are the following.

1. my fusible link is attached to both posts on the firewall does the new one need to do this as well? I can’t find one with the proper end on them.

2. The positive to the starter has no fusible link on it. What does the wiring look like? I am new to automotive wiring.

3. I think the wires actually touched while bolted to the starter I am guessing this would blow the link instantly.

4. The passenger side post on the firewall junction has no wire on it. All the pictures I have seen a red wire is on that post going to the passenger side. Where does this wire go as it’s missing or incorrectly attached somewhere else.

thanks guys. This is my first project vehicle and I developed a rod knock 45 mins after buying it. I am learning as I go.

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[Turbo4whl]

My guess would be this, either the battery positive lead to the starter or the battery ground lead to the engine is bad or loose.

When you tried to crank the engine the high amperage load that passes through the starter found a path through that fuse-able link. There is a good chance the alternator was also part of the path.

 

[SirRobyn0]

@Jrparadis I'll do my best to answer your questions one by one with my answers in italics.

1. my fusible link is attached to both posts on the firewall does the new one need to do this as well? I can’t find one with the proper end on them.
Have you taken the fusible link off? You might find that what connects the fusible link from one side to the other is separate thin metal plate. If not you can solder the new fusible link to the old connector, if you don't solder or don't have the equipment you might be able make up a short length of wire with connectors to bridge those to terminals like the link did. Note: I'm not suggesting to bypass the fusible link in anyway. Also since nothing is connecting to the other terminal it doesn't really matter if it's connected in your current configuration.

2. The positive to the starter has no fusible link on it. What does the wiring look like? I am new to automotive wiring.
I'm not 100% sure what your asking, there are two positive wires running to the starter, the big one that runs directly to the battery and the small wire which leads from the ignition switch, probably though the link you blew and then to the starter. And connects to the small terminal on the starter labeled I, (some solenoids have two small terminals one labeled I and one R printed on the black plastic.) The big wire is always powered, the little wire is only powered when the ignition switch is turned to start position. ground is accomplished though the engine block.

3. I think the wires actually touched while bolted to the starter I am guessing this would blow the link instantly.
I think you mean the two starter wires as in the big wire and the little wire? If that's what your talking about then no. If the two starter wires are touching each other and nothing else then when you connect the battery, the engine would start cranking and never stop until the battery was disconnected. No other ill effects would occur unless left to crank for to long.

4. The passenger side post on the firewall junction has no wire on it. All the pictures I have seen a red wire is on that post going to the passenger side. Where does this wire go as it’s missing or incorrectly attached somewhere else.
No idea. If it worked ok without it before replacing the engine I would not be worried. you could always hit wiring diagrams and trace. In these other pictures you have seen are there two wires on one side like yours is and an additional wire on the other side? Or should that red wire be on the other terminal? I still go back to if it worked like that before replacing engine I'd just leave it.

Finally you need to figure out why the fusible link blew or you'll blow the new one. trace that wire towards the starter (or wherever it goes) and make sure it isn't grounding out. and make sure the connector on the starter end is attached to the terminal correctly and not touching ground. No offence meant by this but also make sure the battery is not hooked up backwards, it's easy enough to do on some rigs especially if the cables area the wrong color or the same color. And make sure that wire isn't caught in anything. Make sure you don't have loose grounds as Tubro4whl has said as that will reek havoc.

 

[75gmck25]

The orange wire running from the junction over to the passenger side usually has an inline fuse, and it connects to the HVAC blower relay . When the wire is missing you won’t have high speed on the blower, but the lower speeds (which go through the resistor pack) should still work.

I also speak from experience - hooking up the battery backwards will burn that fusible link. Factory GM battery cables used black for both positive and negative, so it’s easy to make a mistake.

 

[Termite_Delight]

That's a nice truck you have there! Welcome from the Ottawa Valley

 

[Snoots]

https://www.the12volt.com/info/recwirsz.asp

 

[dsteelejr]

Today when I tried to bump the starter a big puff of smoke appeared.

That’s a good looking square.

I had the exact same thing happen to me nine years ago. My 1980 K25 was my grandpa’s truck and it sat around for 17 years after he passed until I got my hands on it. About a month after driving it I had the same experience. My uncle, who is a retired mechanic, took apart the starter and discovered the starter had an internal short. Not saying that’s what’s happening with yours, but I had the smoke and a fried fusible link.

I’m glad you came to forum for advice. I didn’t know about this forum at the time and just pieced the wiring back together. Luckily I didn’t burn my **** down until I smartened up about wiring and fusible links.

If you don’t have a wiring diagram already you can get one from this forum.
https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

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Here is your junction block. It should have a 10 AWG red wire on the passenger side that connects to the starter post for primary power feed. The driver side has a 16 AWG wire. Tells you right there some POs have had their hand in it and the wiring is not factory.

When you do replace the fusible links, the general rule, unless specifically stated in a wiring diagram or service manual, should be four AWG sizes smaller than the wire it’s protecting. Example, to protect a 10 AWG wire use. 14 AWG fusible link. The fusible links themselves shouldn’t be very long. I make mine three inches.

Good luck.