Fusible Links

I'm doing some wiring on the Jeep and installing new relays for the headlights, park lights, electric fan and horn. I bought a terminal block with the jumper strip from Radio Shack like Boyink shows in his writeup. I'm kind of following MAD Electric's diagrams, which show an 8ga hot wire going to the terminal block, then splitting off to each relay with a 12ga wire protected by a 16ga fusible link (I want to use 10ga to the relays and 14ga fusible links because I have that stuff on hand). Since my terminal block will be installed close to the relays, is it OK to use just the 6" long fusible links connecting the relays to the terminal block? I don't see why not, but thought I'd ask. Thanks.

 

I don't see a problem with that.

 

Thanks Tom. Regarding the fusible links, does anyone have a definitive answer on whether there is a minimum length? Some of mine finished at no more than 2 inches long. Given that they are supposed to melt under extreme heat and prevent fire, I'm wondering if too short a link might let heat pass through too quickly. I searched the Web...Lots of speculation about minimum length...consensus on max length seems to be around 9 inches. I may just make them all 6 inches and put a pigtail loop in them.

 

The ones I have used where made up in the package and are about 6" long. I would run that with a small loop in them.

 

I would use all of whatever they send you. It's a distributed resistance, and you'll lessen the resistance if you shorten it. It may no longer protect the rest of the wiring if shortened.

You want to use the fusible link as the connecting wire between the terminal block and the relays? I would worry that you'd damage the relay connection or terminal block if the fusible link goes. These are made to be used inline in heavier gauge wire, with a butt connector at each end. Unlikely that it will matter, because the links are meant to protect against catastrophe, and a catastrophe is unlikely. Nevertheless, I would put them in the middle of a wire with butt connectors, as they were designed to be used.

 

Looking at the Mad Electrical site, I don;t see any diagram with the links in it. They do show the fusible link with a ring terminal on one end and a butt terminal on the other, so that must be ok. They are going to generate a lot of heat when they blow though, and I think whatever the ring terminal is connected to better be able to withstand quite a lot of heat.

Sounds like you want to use more than one of these links ... I've only seen one of them used at a time, like between the starter solenoid (battery connection) and everything on the car, except the alternator and voltage radiator.

 

You guys are validating my suspicion about the links being too short. I will replace them with longer lengths.

Tim, I'm using a fusible link wherever a hot wire with lots of current supplies a load: for instance,12V 8ga to alternator; 12V 10ga to ignition switch; 12V 10ga to headlight switch; 12V 10ga to the buss feeding the relays. The 12V source is a terminal block near the positive post of the battery jumpered to create a buss bar. And also, from the buss bar to the relays. It may be overkill, but I had some wires melt recently and it scared the crap out of me (I have a friend who says OverKill is OK).

Another point of concern is the terminal, or barrier strips, that I picked up at Radio Shack. I got the idea from Boyink's wiring writeup, but the more I think about it, I'm questioning whether they're really rated for automotive use. They're great because you can get the jumper part, which can be broken apart to make various buss configurations that look clean, eliminating the need for cumbersome jumper wires. But some of them state that they're intended for 16ga wire, while others say 12ga. The screws for the ring terminals are smaller than the terminal blocks you find at the auto parts store. Each connection is rated for 15 amps. I like the idea of using terminal blocks, because I feel that it's a better long term connection than a butt splice, it should make future diagnosing with a test light easier and it would make changing out individual wires easier. But I think maybe I should use the heavier blocks...The whole point of doing this is to get rid of the 45 year old harness that has been hacked into by every previous owner and the current owner as well. Safety is the key, so I don't mind taking a few steps backward to move forward on a better path. And, in case you're wondering why I didn't just buy a pre-made harness, I've had this on my mind for several years now and have just been gathering supplies whenever i could.

Tim, you seem to do a lot of electronics stuff. What is your opinion of the Radio Shack barrier strips for this application?

I will provide some pics to help clarify things.

 

Well, Radieux Shaque is fine as a source of last resort. Something from Mouser or Allied will be much better, quality-wise. I usually pick up old stock of that kind of stuff at ham fests. Let me see what I have in stock.

You know, the single worst liability for electricity and electronics is a mechanical connection. All those convenient connectors in your automobile are there so that the workers can assemble the car quickly, not because they make the wiring more reliable or serviceable. Personally I would eliminate any connectors that were not needed ... crimp, solder, adhesive heat shrink. If you need to remove it, snip the wire. Do you really want to depend on the pressure of a screw for a reliable electrical junction?

 

Here's what I have in my junk box -



All but the two at upper left are Cinch brand. I think that's the nominal USA brand for these. The smaller ones use a #6 screw, the intermediate ones a #8, and the large one at the upper left is #10. Not sure where I got them - some are equipment takeoffs, likely the rest are hamfest impulse buys. These are the connectors you are thinking of?

 

This is the bigger style block (not Radio Shack) that will be fed from the positive post of the battery:

That wire and fusible link feeds the block that feeds the relays. I plan on using similar, separate wires to feed the ignition switch, headlight switch and "always hot" fuse panel.

Here are the relays as they are wired so far. That block is jumpered as a buss bar. That is a Radio Shack block. The short fusible links will be lengthened. I may also move the block further away, because if a link ever does melt, it may damage some other wiring.


Here is the block that 4 of the relays feed. The horn and fan are "straight-through" connections (yellow and center red), while the hi-beams(left red) and lo-beams(right green) are jumpered so that each light can have its own connection point. So far I have only the driver side hi and lo beam connected:


I bought some parts from Speedway too. This headlight switch will replace the broken toggle switch that is in the Jeep now. It is a 3 position switch, I guess...OFF, Park/Running Lights, and Headlights. It could be wired like the original Jeeps, where the park lights come on with the switch pulled halfway out and shut off when the switch is pulled out all the way, powering the headlights. Or it can be wired to have the parking lights come on with the headlights. I'm going to jumper the top and bottom connections for the park lights so that I can have just the park lights on if I want and also have them come on with the headlights.


This will replace the Cherokee column-mounted dimmer switch that doesn't work. I will use a piggyback connector on the hi beam prong to hook up the hi-beam indicator light:


And some fuse blocks to go inside the Jeep:

 

Yes, those are exactly what I have for the "smaller" type terminal blocks...

 

Hmmm...point taken.

 

I also have these in my junk pile ...



I know exactly where these came from - Parts Express. The socket and pigtail have 14 ga wires to the contacts and 18 ga to the relay coil. I would recommend using the sockets rather than the push-on connectors, just so that the conductors are covered, and they can only plug in one way. The relay is the usual type, except that it's waterproof.

http://www.parts-express.com/12-vdc-5-pin-relay-socket-for-bosch-type-relay--330-075
http://www.parts-express.com/12-vdc...relay-spdt-30-40a-with-metal-bracket--330-079

Parts Express is the cheapest around for insulated crimp connectors too. I used to get uninsulated butt splices from Mouser, but they are too expensive now. When I run out, I'll have to buy from Del City, I think. http://www.delcity.net/store/Non!in...dOFM9TkjMpqutr8XTddW2mE1TtdMdSjL3fGgKXCPD_BwE

 

Thanks for the links! I really like the waterproof relays and the sockets as most of my stuff will be under the hood.

 

The better quality type barrier strips can be had from marine suppliers.

 

Mouser has the Cinch barrier strips - http://www.mouser.com/Cinch/Connectors/Terminal-Blocks/Barrier-Terminal-Blocks/_/N-7rqbf?P=1z0zlg6

I expect what you have will be fine, if you decide you want to keep that configuration. Just look at them after 6 mo or so and see if they are corroding. If they are, yo could put them in a box or swap out for some marine grade parts.

 

That's the kind of place I like to use anti-corrosion spray, like S-100 or BoeShield.

 

Thanks again for all the links. I need to get this done ASAP as the Jeep is pretty much my daily driver. I'm sure I'll switch over to the relay sockets down the road. And I'll look into that anti-corrosion spray. I was wondering if there was something available like that to coat things with. To say moisture isn't a major problem here would be an understatement, that's the main reason I wasn't too hesitant to put most of this under the hood...plus I hate working up under the dash.

 

Nice components/ideas to include when I rewire my '66.
My favorite anti-corrosion spray is "CRC Marine Corrosion Inhibitor". It sprays on thin and runny, then the carrier evaporates leaving a nice waxy film that "heals" when scratched. It isn't too bad at attracting dust/dirt once dry. I use this stuff for everything, electrical and otherwise!
-Donny

 

I hit a bit of a snag here, otherwise known as a brain fart. I installed the "Always Hot" fuse panel using this type:

Then it dawned on me that, for anything running through the relays, I need access to both sides of the fuse. Something like this:

Correct? The first type shown can be used, but only for things like power into the turn signal flasher, hazard flasher, brake light switch and heater fan switch, right? So, for instance, to wire the headlights, I need to bring power into the headlight switch, then back out to one side of a fuse, out the other side the fuse to the dimmer switch, THEN to the high and low beam relays. You cant do that with the first type of fuse panel shown, can you?