[patrickt]

If the fuse doesn't blow, then it's the right size. Unlike a circuit breaker, which will blow at a lower current spec as it gets hotter. A 40 amp circuit breaker that is mounted to your firewall under the hood can easily blow at, say, 30 amps. The circuit breaker manufacturer has a chart that shows you about where it clicks off depending on how hot it is, but most car guys on here don't know that and just assume that 40 amps means 40 amps....