73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Electrical => Topic started by: watahyahknow on March 26, 2019, 03:19:23 PM
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hi everyone , been a while since i was here (cashflow problems and lack of time mostly )
i have a problem after hooking up the battery terminals backward :-[, (truck is stored and i needed to move it so i hooked up the battery in low light and done it wrong) right after connecting the terminal without the contact on i heared sumting pop near the dash but cant find where
its a 86 c10 and a picture pointing me to where to look would realy help as i only heared recently about fusible links and stuff like that
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Search fusible links on here. It's been discussed countless times.
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When I made the same error (isn't it great how the original battery cables were both black?), it burned the fusible link that runs straight down from the junction on the firewall next to the brake booster. I bought a 14 gauge GM fusible link from the parts store and spliced it in as a replacement.
Bruce
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Wow what luck to find what I need right here in the recent topics. So I did the same thing as the initial poster, and it sounds like I burnt the same exact wire on my 85 C10. It's the only wire going to that junction box that has two separate sized terminals on the connection. I'm confused with the "fusible link" part. I bought some 14 gauge wire and used a butt connector to reconnect the line. I now have my power and the truck turns over, but acts like it's getting no spark. Where am I looking or this fusible link?
Thanks for any help. I just did the body work and paint and am now into the interior on my restoration project. I need to get this thing running again!
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Post a pic. Sounds like the wire you replaced with 14-gauge primary wire was actually the fusible link. Fusible links are a subclass of fuses that are ultra-high-current, very slow acting, and installed at the inception of a main power bus. Replacement criteria are very specific. The factory fusible link at the firewall junction block on your 85 C10 is [was] 6" long and made from 16-gauge fusible wire. Primary wire IS NOT a viable replacement for fusible wire! In the interim, disconnect the battery until the fusible link is properly replaced with the correct gauge and length or you will run the risk of electrical fire and burning the truck to the ground. See the 1985 Wiring Manual (http://www.73-87chevytrucks.com/techinfo/7387CKMans//Wiring/ST_352_85_1985_Chevrolet_GMC_Light_Truc_Wiring_Manual_CK_10_30_Only.pdf#page=9), the topic Fusible Links in Fuses and Circuit Protection (http://forum.73-87chevytrucks.com/smforum/index.php?topic=35587.msg300859#msg300859), and How to make a Fusible Link (http://forum.73-87chevytrucks.com/smforum/index.php?topic=11972.msg45217#msg45217) for relevant information.
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I think you're right. The wire burned above the link, so I just reconnected the wire. How do I replaced the fusible link? Do I cut the two wired below it? If this first link doesn't work I'll post another link. Right now I"m going outside to disconnect that battery!
(https://i.postimg.cc/Z0g528PW/IMG-0645.jpg) (https://postimg.cc/Z0g528PW)
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The 1" long black cylinder located between the two 12-gauge wires, below, and the single wire, above, is just a urethane encased butt splice. Cut the two wires directly below the splice and join the replacement 16-gauge fusible link to the stripped ends of the wire pair. It may be easier to use an uninsulated 10-12 gauge butt splice to join the three wires together. Solder the connection using 60/40 rosin core solder as shown in Vile's thread and then insulate with some marine grade (adhesive lined, dual wall, polyolefin) heat shrink cut to about twice the length of the butt splice. Likewise, crimp and solder an uninsulated ring terminal onto the free end of the link and shrink-seal the terminal barrel.
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Thanks a bunch. Some of that might be beyond my skill level but at least I know what needs done. I used a heat gun to seal the butt joint on this repair, I don't own a soldering gun and rather not learn under the hood! I would feel better about pulling it off if it was just two wires needing joined, not two 12 gauge and the 16 gauge link.
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The 1" long black cylinder located between the two 12-gauge wires, below, and the single wire, above, is just a urethane encased butt splice. Cut the two wires directly below the splice and join the replacement 16-gauge fusible link to the stripped ends of the wire pair. It may be easier to use an uninsulated 10-12 gauge butt splice to join the three wires together. Solder the connection using 60/40 rosin core solder as shown in Vile's thread and then insulate with some marine grade (adhesive lined, dual wall, polyolefin) heat shrink cut to about twice the length of the butt splice. Likewise, crimp and solder an uninsulated ring terminal onto the free end of the link and shrink-seal the terminal barrel.
So I saw on a 67-72 forum a guy saying that you can put a separate fusible link on each of the 12 gauge wires instead of trying to splice all three together. I even found butt connectors on Waytek.com that are 10-12ga on one end and 14-16ga on the other, making that connection super easy. Any thoughts? My only concern is the connection at the terminal block. I'll need to get two fusible link wires onto that terminal instead of one.
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It's not an optimum scenario because one of the 12-ga red wires connects to the alternator output post and the other 12-ga red wire feeds into the cab. The factory fusible link exists between the junction of the two red wires and the battery, whereas the 12-ga red wires are connected directly together. Refer to the 1985 Wiring Manual that I linked earlier.
Essentially, this means that the addition of a second fuse link introduces a double-length "primary fuse" between the alternator and cabin electrical loads where, before, there was none. Under normal circumstances, the double fusible link solution may function without significant repercussions. However, under severe circumstances, such as extreme electrical loads, the voltage supplied to the cabin appliances may diminish by transferring voltage drop to the fusible links and one or both fuse links might fail, leaving the truck stranded. Although it is unlikely that this will occur, the potential is there commensurate to the modification. So the guy on the other forum was partially correct, excluding special circumstances.
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Sorry to drag this thread up again but I've been busy in the interior of my truck and haven't messed with this wiring yet. I came across these 3-ways. Obviously one drawback is your going to be putting the 16 gauge fusible link in a 12/10 opening, or if you buy the 16/14's instead you'll need to fit two 12 gauge wires into 16/14 openings. Besides that though is there any reason why you wouldn't want to use a 3 way butt connector like this to rejoin these wires?
http://www.genuinedealz.com/3-way-wire-splice-butt-connector-w-adhesive-heat-shrink-12-10-awg
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Pick up an 8-gauge butt splice. Cut it in half. Insert the two 12-gauge wires into one end and the 16-gauge link into the other so that all of the wires overlap (image). Crimp, solder and shrink seal. Voila!
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I do not recommend combining two wires into one splice just for convenience with a fusible link.
- 12 gauge wire is good for up to about 35 amps
- Two 12 gauge wires could be intended to handle as much as 70 amps total (although not likely)
- 16 gauge fusible link is designed to protect a single 12 gauge wire, so it should burn through at about 20 amps to protect the wire
- The way that splice is plumbed, it is protecting both wires and may burn through at about 20+ amps total current.
Most parts stores have standard GM fusible link wiring like this 14 gauge link that is designed to protect a 10 gauge wire. https://www.amazon.com/Dorman-Help-85620-Gauge-Fusible/dp/B000COD0TW
You can also buy bulk fusible link wire in different gauges from NAPA and make your own links by crimping a connector on each end.
My truck came with a 63 amp 10si alternator, and IIRC the stock charge wire and fuse-box feed wires connected to the starter are both 10 gauge with a 14 gauge fusible link. I now have a 93 amp 12si alternator, and upgraded to an 8 gauge charge wire by pulling one off a newer 88+ GM truck that had a higher amp alternator. The new wire had a black molded 12 gauge fusible link.
Bruce
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Interesting bd, I guess I'm missing the need to cut in half? Wouldn't you just get all three wires in the middle and crimp once, instead of the normal two crimps? I'm assuming by your reply that you would avoid the three way butt connectors?
75gmck25 - I believe in my situation this was how it was from the factory, not doing by convenience. The 16 gauge fusible link protected two 12 gauge wires. I've already purchased the new fusible link and attached it to the double ring terminal that goes to the terminal box. I"m just looking at options to attach the two 12 gauge wires back to the fusible link. (don't currently own a solder gun)
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Interesting bd, I guess I'm missing the need to cut in half? Wouldn't you just get all three wires in the middle and crimp once, instead of the normal two crimps? I'm assuming by your reply that you would avoid the three way butt connectors?
There are two types of electrical wire splice that fall under the general category of barrel splices that are relatively common: 1) butt splice - wires enter from opposite ends and crimp independently inside the splice without overlapping, the ends of the wires may come into direct contact and 2) parallel splice - wires enter from opposite ends and overlap 100%, sharing one common center crimp. Most OEM wire splices are parallel splices.
If you inspect a butt splice, notice that it is dimpled at the center, which prevents wires from penetrating the splice past the center point. This ensures that wires entering the splice from opposite ends penetrate to the same depth without interference. A parallel splice is less than one-half the length of a butt splice and lacks the center dimple, allowing full penetration and overlap of all wires entering the splice. The reasons for cutting a butt splice in half are: 1) to eliminate the center dimple, 2) to shorten the overall length, making it more compact and 3) parallel splices typically are sold in minimum quantities of 100 at about 70¢ a pop. $70 is a lot of jing to invest in 100 pieces if you are making only one repair. Granted, cutting a butt splice in half is a tedious PITA, but much cheaper than the alternative.
You may ask, "Why use a barrel splice at all? Why not just expand the wire strands and join the ends of the wires directly, soldering them together and shrink sealing or taping without a barrel splice?" The answer lies in the benefits of mechanical strength and wire containment that are imparted to the joint. A barrel spice prevents separation of the wires in the event that the solder heats to melting - not a common scenario, but it does occur.
I do not and never have appreciated three-way terminal splices, since they are mechanically riveted at the center joint, which makes them bulky and allows the joint to rotate, introducing the potential for loosening and gradual joint oxidation (aka, connection degradation). Connection degradation causes excessive circuit resistance resulting in unwanted voltage drop across the joint, which builds heat, degrading the connection further, and so on. Even if you solder the joint, a three-way splice remains bulky and is difficult to effectively insulate or protect from exposure to dust and moisture. Of less importance, it is unsightly.
I do not recommend combining two wires into one splice just for convenience with a fusible link.
- 12 gauge wire is good for up to about 35 amps
- Two 12 gauge wires could be intended to handle as much as 70 amps total (although not likely)
- 16 gauge fusible link is designed to protect a single 12 gauge wire, so it should burn through at about 20 amps to protect the wire
- The way that splice is plumbed, it is protecting both wires and may burn through at about 20+ amps total current.
Most parts stores have standard GM fusible link wiring like this 14 gauge link that is designed to protect a 10 gauge wire. https://www.amazon.com/Dorman-Help-85620-Gauge-Fusible/dp/B000COD0TW
You can also buy bulk fusible link wire in different gauges from NAPA and make your own links by crimping a connector on each end.
My truck came with a 63 amp 10si alternator, and IIRC the stock charge wire and fuse-box feed wires connected to the starter are both 10 gauge with a 14 gauge fusible link. I now have a 93 amp 12si alternator, and upgraded to an 8 gauge charge wire by pulling one off a newer 88+ GM truck that had a higher amp alternator. The new wire had a black molded 12 gauge fusible link.
Bruce
The OEM circuit configuration does not impose a burden on the 16-gauge fusible link to carry "as many as 70 amps" since only one of the paired 12-gauge wires connects to an actual load.
One of the paired 12-gauge wires connects to the alternator - a power source. With the engine running, alternator output divides at the triple junction with the fusible link between the battery and the cabin/ignition loads. The triple junction is the point where one load circuit (the combination of cab and ignition) connects to two power sources (the battery and alternator). The link is located between the battery and the triple junction. Effectively, the link carries current in one direction from the battery toward the cabin and ignition loads while the engine isn't running, then carries current in the opposite direction from the alternator toward the battery while the engine is running and the alternator is charging. With the engine running the alternator also supplies the cabin/ignition loads directly, without involving the fusible link. The only circumstances in which the alternator becomes a load is if it short circuits internally or if the battery cables are switched at the battery, forward biasing the alternator diodes, in which cases the fusible link melts open.
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GM recommends using splice clips for soldering splice connections and these are what I use as well
https://www.fastenal.com/products/details/11237902
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Splice clips can be found at ClipsAndFasteners.com (http://www.clipsandfasteners.com/v/vspfiles/assets/images/auveco_catalog150.pdf) as well for a decent price.
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Thanks bd, your replies always clear things up! So I found a place that will sell me 20 of these for under 40 cents each. Is this the correct item? This looks like the easiest and neatest way to combine the wires back together.
https://www.waytekwire.com/item/33570/Molex-19206-0012-Parallel-Splice-Connector-/
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Those should work. I recommend that you strip off the vinyl jacket before crimping and then solder the joint after crimping. Once the joint is crimped and soldered it can be sealed in marine grade heat shrink to insulate the splice and reject dust and moisture.