Automotive Fuses: A Somewhat Brief Tutorial (with Illustrations)

Have you replaced a fuse on one of your modern daily-driver automobiles recently? It’s likely you have not. Today’s motor vehicles have much more sophisticated electrical systems, and while your typical 2017 four-wheeled 2.5 ton behemoth still uses fuses, the days of fuses just “wearing out” are behind us.

If you have needed to replace a fuse, the first trick may have been to locate the fuse boxes. My wife’s 2017 Honda Odyssey has FIVE fuse boxes: two in the engine compartment, two under the dash, and one at the rear, containing a total of 107 fuses. It makes me pity the shop tech who needs to fault-trace an intermittent electrical problem.

My 1967 Alfa Romeo GT 1300 Junior, by contrast, has one fuse box, located in the engine compartment. Access to it is easy, as it’s mounted high up, on the right-side inner fender. There are a total of 10 fuses: one for ignition, five for exterior lighting, and three which are helpfully marked “other electric devices” (of which there are few; my Alfa lacks the power sliding doors, climate control, and ‘Lane Departure Warning’ of my wife’s minivan).

Ten little fuses, all in a row. Note bi-lingual fuse box cover.

Italian cars get a bad rap for their supposed temperamental electrics. But there’s not been a lick of an issue with mine, save for a battery which died shortly after I got the car (because it was 10 years old at that point). Preventative maintenance goes a long way toward keeping the electrons flowing in the proper direction and in a complete circuit.

With any old car, I will gladly get on my soapbox and preach the ’12-Volt Gospel’: 99% of electrical gremlins are caused by poor connections. Terminals must be clean and tight; ground wires must be securely connected to clean ground; and fuses and their terminals must be clean, tight, and protected with dielectric grease. In no case should an electrical component be replaced without first ensuring that all connections, hold-downs, and crimped or soldered terminals are in the best shape they can be.

Soon after acquiring the Alfa, I removed all 10 of the European-style ceramic fuses, cleaned the spring-tensioned holders with a brass brush, and bent the holders inward to make them tighter. Next, I applied a light coating of dielectric grease. Upon reinstalling the fuses, I ran continuity tests with my multimeter to check that there was minimal (ideally, close to zero) resistance in the connections.

This dielectric grease is magical stuff. It seems counter-intuitive to grease electrical connections, but it prevents corrosion from forming. You still need to have a strong mechanical connection. It should be used on battery terminals and spark plug boots as well as fuses. Don’t waste your $1.99 buying the point-of-purchase 0.001 oz. packet at the retail store checkout counter. I bought a 5-ounce tube about four years ago, and even after multiple applications on multiple cars, I’ve only used about 25% of it.

Dynatex brand dielectric grease – I use it frequently on electrical work

While on the subject of fuses: I recently cleaned out an old shoe box full of automotive miscellany which had belonged to my dad. In it were several tins of glass-style fuses. While none of the cars I own today use this style, my ’68 Mustang did, and I recall how difficult it was to reach the fuse box on that car, as it was mounted above the gas pedal.

Buss brand glass fuses – note old & new style packaging

Some people refer to these as Buss fuses, however, that is a brand name. According to Wikipedia, these fuses were also known as “SFE” fuses because they were developed by the Society of Fuse Engineers.  They varied in ratings between 4 and 30 amps, and in corresponding lengths between 5/8” and 1&7/16”. This was done by design in order to help prevent a fuse of incorrect amperage from being inserted.

Automotive glass fuses

 

Red Line brand fuses – box states that company is from N.Y.

 

Opening these is like going on an archeological dig

If you have a newer car, here’s hoping that you never need to replace a fuse (much less find the fuse box). If you have an older car, here’s hoping that you invest in a tube of dielectric grease, and in a half-hour of preventative maintenance. Let me know how it works out.

 

All photographs copyright © 2017 Richard A. Reina. Photos may not be copied or reproduced without express written permission.

Special photographic note: the 4 photos of the glass fuses were taken with a FILM camera, specifically, my Nikon EM, using Kodak Gold ISO 200 film.


FUN FACT OF THE WEEK

On January 14, 1885, Thomas A. Edison of Menlo Park NJ, applied for a U.S. Patent for his invention of a “fuse-block”, to act as an electrical protection device.

 

 

 

 

4 thoughts on “Automotive Fuses: A Somewhat Brief Tutorial (with Illustrations)

  1. You probably remember one of the simplest and easy-to-access fuse boxes ever on the 122S with only four fuses! It was always satisfying when a panicked customer would drive in with half of the car’s electrical components inoperative and one could open the hood, clean the fuse holder, replace that stubby little 25A fuse and get them on the way in two minutes.

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  2. Ah Bob, thanks for the comment and the memory! By the time I started wrenching on Volvos, it was almost exclusively 140s and 240s, but the same general principle applied. Those fuse boxes were immediately accessible once the driver’s door was opened. In some cases, the fuse didn’t need to be replaced, just spun it its holder, which cleaned the contacts and restored the connection! The look on the owner’s face was priceless, especially when I as the Service Advisor said “no charge!”.

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  3. Nice article Rich. I also had a collection of “buss” fuses from my Dad’s toolbox. Some day my grandkids will write articles about the historic junk they found in mine, like a small slide rule.

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