After fully educating myself about fusible links and how they work, I decided -- hands down -- I'd rather have a fusible link than a circuit breaker or in-line fuse for certain things (like my electric fan) any day.
"What if a fusible link goes while I'm on the road?" was my first question ... but I didn't realize how dependable fusible links were when I asked that question! First of all, You can easily keep a spare handy. But, more importantly, fusible links NEVER fry unless there's a VERY serious problem that needs your immediate attention (like a major power wire grounding against metal!); a problem that a circuit breaker or in-line fuse could mask well enough to have you finding your car in flames.
An in-line fuse on a 30-amp electric fan circuit (as I discovered) won't last very long. When that fan kicks in, it's more likely to pull 60 amps (initially) than 30, and after a dozen times or so an in-line fuse will give up it's ghost and fry -- it's a gradual breakdown though.
And, just like an in-line fuse, a 30-amp circuit breaker is subject to wearing out and eventually frying ... it just takes longer.
A fusible link will never wear out -- you can see many of them in older cars still doing their job after 20 years or more.
1 - Rule of thumb: 4 gauges smaller = the right fusible link. For an 8-gauge wire, you'll want a 12-gauge fusible link; for a 10-gauge wire, you'll want a 14-gauge fusible link; for a 12-gauge wire, you'll want a 16-gauge fusible link, etc.
2 - You don't want to use regular wire ... fusible links are different and have a non-flamable insulation. You can buy fusible links here:
3 - NEVER USE FUSIBLE LINKS IN YOUR INTERIOR! Fusible links, when they do fry, spark like crazy ... keep them out of your interior and keep them away from gas lines; anything ignitable.
As part of my Mad Electrical Improvements project, I decided to put relays into my headlight wiring scheme ... one relay for the high-beams and one for the low-beams. You can read Mark Hamilton's article about it here:
It's a pretty simple matter to find the two wires that come from your fuse box and send power to your high-beams and low-beams. Once you locate those two wires in the engine compartment area, you just cut them.
1 - Cut the low-beam wire.
2 - Take the section that comes from the fuse box and connect that to the white wire (aka #86) on the relay for the low-beams.
3 - Take the other section that goes to the left headlight and connect that to the yellow wire (aka #87) on the relay for the low-beams.
4 - Cut the high-beam wire.
5 - Take the section that comes from the fuse box and connect that to the white wire (aka #86) on the relay for the high-beams.
6 - Take the other section that goes to the left headlight and connect that to the yellow wire (aka #87) on the relay for the high-beams.
7 - Take the two black wires, one from each relay, (aka #85) and ground them to the frame.
8 - Take the two red wires, one from each relay, (aka #30) and connect them to a steady power source. If you're providing power to your engine area with a terminal block as I have, you'll connect a fusible link to the end of each wire and then connect the fusible link to the terminal block (see schematic below).
This, combined with the efforts described in my first 2 journals was all very worthwhile! Feeding power to the engine area with two terminal blocks, supplying a full 14.2 volts ... feeding the alternator with an 8-gauge wire, setting up my ignition-to-alternator wire with a diode and running the regulator wire to the terminal block, made my engine perform better -- and my voltage gauge smiles like it's on a happy vacation! Then, wiring my electric fan with double relays and a fusible link (instead of a circuit breaker) made a huge difference; my voltage gauge doesn't show any reaction at all when the fan kicks in ... and, finally, putting these relays in for my headlights surprised me tonight when I was driving at night and saw how much brighter my headlights are!
If you've been thinking about doing all this, stop thinking about it and do it! I couldn't be happier with the results I'm seeing.
After having my new Walker radiator installed with a 16-inch electric fan, I was very dissatisfied with the wiring situation. After reading about it all at MadElectrical.com, I decided to follow Mark Hamilton's advice. I ordered two relay kits, along with a bunch of other stuff, and rewired my fan. If you want to read about it, scroll down to ELECTRIC RADIATOR FAN SYSTEMS on this page:
I looked at the wiring the mechanic had originally done when he installed my new radiator and there were six things I didn't like:
1 - He ran the fan wires, which are located on the driver side of the fan, over to the passenger-side of the engine compartment and put the relay there.
2 - He ran the #86 relay wire to the ignition via my electric choke wire ... which is okay, I guess, but I've got a dedicated fuse in my fuse box, from my EZ-Wire installation, just for that.
3 - He grounded the fan on a painted surface in the engine compartment - this guy's a good mechanic but obviously doesn't like electrical work.
4 - He installed a faulty circuit breaker and didn't know it or decided to ignore it.
5 - He ran a (whimpy) 14-gauge wire to my battery to power the fan with.
6 - When the fan kicked in, even after I fixed the faulty circuit breaker, my voltage gauge would drop way down and wouldn't come back up for quite a while.
Anyway, after mounting two terminal blocks on my firewall, creating a full 14.2-volt power station there (see my entry titled WIRING YOUR ENGINE AREA FOR BEST RESULTS), I mounted two relays to take care of my 16-inch electric fan.
First I disconnected my battery and mounted the two relays on the driver side in my engine compartment. Then I measured the red wires from #30 on both relays to the terminal block so I could solder them to a fusible link and make a connection to the full power there at the firewall.
Next, I went under my dash and found the Electric Fan wire from my EZ-Wire kit that I had stashed away for future use ... placed a 30 amp fuse for it in the fuse box ... ran the wire out to the engine compartment and connected it to the #86 plugs on both relays.
Then I took both wires from the #85 plugs on both relays and butt-connected them to the thermostat/switch on my mainifold and then butt-connected the wires from the #87 plugs on both relays to the electric fan. And, finally, I set up a nice bare metal ground on my frame for the Ground wire on the electric fan.
Everything worked like a charm! If I'm sitting at a traffic light and the fan kicks in, the needle bumps down a half-volt for a quarter-second and comes right back up. If I'm driving and the fan kicks in, the voltage gauge doesn't even react.
There's this web site called MadElectrical.com that is an unbelievably cool resource for understanding electrical systems in street rods. After reading a bunch of Mark Hamilton's articles in the Electrical Tech section, I decided to make some improvements on that EZ-Wire installation I did last year.
Also, my new Walker radiator is working beautifully, but the 16-inch electric fan was wired poorly and that really started me reading the info available at the Mad Electrical site. I wound up purchasing all kinds of goodies and today I started by installing terminal blocks on my firewall. This is in the interest of powering everything in the engine area directly from the firewall, instead of going through the fuse box under the dash, back out to the engine area -- wasting wire and losing voltage, as is done with most wire kits.
First I disconnected my battery and installed two terminal blocks ... then I ran an 8 gauge wire from the battery-positive to the #1 terminal block, which gives me full power at the firewall (see schematic below).
Next, I rewired my alternator using the Mad Electrical Alternator Wiring Kit -- the old setup had no diode on the #1 wire (going to the ignition) and the #2 wire, which talks to the regulator, was just piggy-backed over to the BAT connection on the back of the alternator. I soldered a diode in-line on the #1 wire - this keeps voltage flowing in only one direction (towards the alternator) and insures against engine "run-on" ... then I ran the #2 wire over to the terminal block where the alt. regulator could read the voltage that is actually being distributed to everything.
All the above is explained in the booklet that comes with Mad Electrical's Alternator Kit.
NOTE: The order of the connectors on each terminal block is important; they need to be arranged bottom-to-top / largest-to-smallest.
1 - On T-block #1, I placed the 8-gauge jump wire on top of the 8-gauge battery wire and ran it over to T-block #2.
2 - On T-block #1, I placed the 8-gauge alternator BAT wire on top of the 8-gauge jump wire -- this one has a 12-gauge fusible link located at the alternator BAT connection.
3 - On T-block #1, I placed the 12-gauge alt. regulator wire on top of the 8-gauge alternator BAT wire -- this one has a 16-gauge fusible link located at the T-block.
4 - On T-block #2, I placed the 12-gauge main power wire, that goes to the fuse box under my dash, over the 8-gauge jump wire -- this one also has a 16-gauge fusible link located at the T-block.
5 - I put split loom over all the wires, vinyl tie straps where needed, re-connected the battery and started her up to make sure all was cool; it was.
It's amazing how you can feel each little change you make ... when I turn the engine off, for example, it really shuts off! -- that diode I installed on the alternator #1 wire makes a noticeable difference! The engine starts up quicker and with more "confidence" than it did before, too. Also, it's very comforting to know that my alternator is reading and sending more accurately and that my dash area is getting the full 14.2 volts it's suppose to get.