ET-102 explains the SLOW BLOW FUSES used in the MGA and why you should not use "standard" fuses.

At 06:49 AM 5/15/02 -0700, Scott Willis wrote:
>"I broke a 35 amp fuse in my MGA box. It's shorter than all other fuses I have. Is that an odd size that I have to order from Moss etc. or should it be avail at auto zone?"

DO NOT USE A STANDARD 35 AMP FUSE. It is not an odd size, but it is an odd type of fuse. It is actually a 17/35 amp slow blow fuse that will carry 17 amps indefinitly but will blow immediately at 35 amps. If you install a regular 35 amp fuse you run the risk of frying your wiring harness. This "special" fuse may carry 20 amps for a minute or so before it blows. The more current it sees the quicker it will blow, but it may even carry a 30 amp spike for a couple of seconds without blowing.

The reason for using the slow blow type of fuse is because the wiring size is relatively small compared to the current load it is expected to carry. The MGA only has two fuses, and one of those (the 25/50 fuse) is dedicated just to the horn. Everything else in the car that _IS_ fused (not everything mind you) runs through the 17/35 fuse, and some of the wiring is only 18 gauge. If you had a short in a tail light fixture you could draw perhaps 30 amps continuously and never blow the 35 amp regular type fuse. Even though you have a dead short the current may never go higher, because of the resistance of the long length of small gauge wire. Drawing 30 amps continuously on the (small) 18 gauge wire will likely make the wire so hot as to melt down the insulation. The 17 amp slow blow fuse takes care of this condition.

Best regards,
Barney Gaylord