OK I have a bad 5A fuse on the dash lights and now the question is why. Does this ALWAYS indicate an electrical problem in the circuit or can the fuse just get old and break?

Thanks-Dave.

OK I have a bad 5A fuse on the dash lights and now the question is why. Does this ALWAYS indicate an electrical problem in the circuit or can the fuse just get old and break?

Thanks-Dave.

It might be a faulty fuse if it happened once, but not twice. A fuse is set to melt at currents above, say 5 Amps. If you are running with no headroom, say 4 Amps, it could weaken the metal. Do you know what's running off that 5 Amp fuse and how much you are drawing?

My first reaction is to replace it and see what happens. At 5 Amps there really is no jeopardy other than another blown fuse.

Chuck

This is the 5 amp circuit for the instrument lamps. I also have added a small tach (1 bulb) and an oil pressure/water temp gauge pod that has 2 bulbs. While the wiring diagram in the manual says it is a 5 amp circuit, there was a 4 amp fuse installed. So maybe I was running right at 4 amps.

However, this has been the set up for about 3 years without problems.

thanks again.

My car used to pop that fuse frequently. It turned out that the clips that hold the fuse were corroded. The extra resistance caused the fuse to heat up an prematurely blow the fuse. Cleaning the clips (use a brass gun cleaning brush) helped a lot, but I fixed it permanently by wrapping a thin strand of copper wire around the metal contacts on the fuse to increase the contact squeeze force. I checked this out by putting in a new fuse and turning on the lights and putting a finger on each end of the fuse. It was too hot to touch, so I knew I had a resistance problem.

My car used to pop that fuse frequently. It turned out that the clips that hold the fuse were corroded. The extra resistance caused the fuse to heat up an prematurely blow the fuse. Cleaning the clips (use a brass gun cleaning brush) helped a lot, but I fixed it permanently by wrapping a thin strand of copper wire around the metal contacts on the fuse to increase the contact squeeze force. I checked this out by putting in a new fuse and turning on the lights and putting a finger on each end of the fuse. It was too hot to touch, so I knew I had a resistance problem.

Yep. Fuses blow by heat. If you get them hot enough they will blow without any current at all!
They do fail over time depending on how much they are loaded. A 5A fuse that has 4.9A of load through it will not last as long as a 5A fuse with 2A of load depending on temperature.

If you operate an automotive (this does not apply to other types of fuses) 32V DC fuse at 110% of rating it will take a minimum of 100 hrs of operation to blow but might never blow due to manufacturing and material variations.
If you run it at 135% of rating it may blow in 0.75 seconds but might take as long as 600 seconds.

Fuse rating are specified for a fixed temperature of 25 degrees C. They derate with temperature so that by 60 degrees C they are only good for 95% of their rating. If you drop the temperature to -40 degrees C they can take 110% of their rating.

Most automotive fuses have to meet a spec for the OEMs, SAE J2077.

Ron