Fusible link question

[Timber]

I'm trying to chase down a gremlin and haven't repaired a fusible link before. How do the plastic covers at the junction open? My eyes aren't what they used to be. Thanks.

 

[cucvrus]

Just cut them off. They are just fancy OEM butt connectors.

 

[Timber]

Crap. I was hoping to test voltage without destroying them. I don't know that they aren't good. I lost lights/horn earlier this week, trying to sort it out. Thanks.

 

[cucvrus]

Check te 30 amp fuse on the right side midway on your fuse box. They are known for melting and getting over loaded. Check that area first.

 

[Timber]

I checked that one first, but thanks, I did meant to check them all again today. There is an orange wire and orange wire with a black stripe coming off the back of the blackout light switch harness, both of them are reading 5.5 to 5.8 volts. And there is an orange wire and white wire coming into the headlight switch, both of those are reading the same 5.5 to 5.8 volts. I checked those because I read somewhere here the blackout light switch can make you lose all lights and horn, but I also read where a bad fusible link can give low readings like I'm getting. I stink with wiring diagrams, but I'm trying to trace it back.

 

[Timber]

I counted seven fusible links at the engine wiring harness block on the firewall and probed both sides of each one with a test light - they all appeared to light up the same. I'm going to separate the fuse block at the firewall next to see what I can find and clean it up while I'm there. I'm open to suggestions. BTW, the 30 amp fuse is a little melted, but tests good for continuity and reads voltage on each side on the multimeter. And somewhere in all my probing and wiggling the horn started working again.

 

[Timber]

I've had this truck a good five years now and have gotten by without cleaning connections, always knew I had it coming. I put new batteries in a few weeks ago and cleaned the terminals when I did. Instead of going straight to separating the fuse panel at the firewall for cleaning and inspection, I started at the distribution block behind the back battery. I took those connections apart one at a time and cleaned them up with a wire brush and put them back together with a thin coat of dielectric grease. Then I did the same for the ground on the firewall behind the transmission dipstick and the one behind the front battery. I also removed the junction block in the cab and the power and ground wires running to it while I could. Some joy here, I have brake lights and turn signals again. Still no headlights, but I'll keep at it tomorrow.

 

[MarcusOReallyus]

1. That 30 amp fuse is a very large source of various problems. It has a mysterious-seeming linkage to the horn circuit. You really, really, really need to read this thread, which will explain the connection and why it matters to your problem. Read it from start to finish - it will seem irrelevant at first but you really need to read the whole thing.
2. A connection can show the correct voltage when tested with a voltmeter, but not when tested with a load on it. This is because corrosion can set in to various places and corroded wires or connections offer a high resistance to a current. When there is no current flow (like when probing with a voltmeter), the voltage looks normal. But when the circuit is loaded, the current can't flow like it normally would, causing low voltage downstream from the point of high resistance.
3. Don't worry about cutting off those factory butt connectors. No big deal. Just replace them with good quality (like 3M) connectors that have built-in heat shrink. I much prefer the kind that are translucent, as that allows me to keep an eye on the connection.

 

[Timber]

Thanks for that, I'll read it tonight. I read Warthog's thread with the explanations and diagrams but didn't see this one.

 

[Warthog]

For fusible link info, read the Fusible Links 101 thread in the CUCV Helpful Threads sticky.

 

[Timber]

Thanks Warthog, I searched this a few different ways, did some reading and tested a good bit before I posted but you guys pointed out two I missed. I'll order the LMC harness, snip the diode and eliminate the suppressor on the horn circuit. I'm kinda in the spot as the OP on the thread MarcusO linked - should I work on it until it works again and THEN install the LMC relay harness, or just install it and see if the headlights work again? My mind tells me to fix what I've got, then install the patch/fix/upgrade, but you and doghead understand the electrical better than I ever will.

 

[Timber]

I have the LMC harness installed but have not performed the horn vasectomy yet. Still no lights. I'm still planning on snipping the diode and suppressor, but thought I'd have lights at this point. I'm starting to suspect the switch. Any thoughts? Thanks.

 

[Warthog]

Do you have a 12v test light? If not you may want to buy one. They are very handy in tracing down electrical issues.



I would use this thread and start from the begining of the circuit until you find the problem. It is broken down into easy steps

http://www.steelsoldiers.com/showthread.php?87544-CUCV-Headlight-Circuit

Now I do have to ask the question: Is the blackout light in the "service" position?

 

[Timber]

Yessir, test light and multimeter in hand. Trouble is, I'm an older and larger mammal that doesn't understand vehicle electrics so good. If all the wiring were laid out on a table I could probably follow the schematics and figure it out. But getting my head/arms/hands under the dash where I can see and probe is tricky. I know I have hot (forget how many volts) going into the OEM headlight switch, I need to check the yellow wire coming out and see if it's hot with the knob pulled out. I appreciate the help.

 

[Timber]

I have lights again. But the headlight fuse isn't getting good contact from overheating, so I'll cut those horn wires this weekend and hopefully remove the rest of the overload from the circuit. If I take the fuse panel apart can I bend the contacts back so it will grab the fuse good again?

 

[MarcusOReallyus]

You can usually do that without taking anything apart. Clean them with emery cloth, give them a shot of contact cleaner (CRC is a good brand), and get in there with a small pair of bent-needlenose pliers.

 

[Timber]

That's what I ended up doing. I've got heat damage to that fuse spot. I wish it were easy to replace. My son has asked for this to be his first car and will be 16 soon, so that worries me a little. At least with the relay harness on and the offending horn pieces removed, maybe it won't get any worse. I've got a few months, so we'll see how it goes. I appreciate all the help.

 

[msg bruce]

Do we need to keep all the fuseable link or can they simply be replaced with a fuse ?

 

[Warthog]

Read the Fusible Link 101 thread in the CUCV Helpful Threads sticky. It helps answer your question.

The simple answer is no. But if you have a knowledge of electrical circuits and load calculations it may be possible to properly replace them with the properly sized maxi-fuse.

 

[cucvrus]

Fuseable link is a different gizmo then a fuse. A fuse just blows. A fusable link takes a little more abuse. That is my experience. So I would just keep the fusable links. But I am not an electrical engineer.