You can also get ptc (positive temperature coefficient) resettable fuses
which will go from low resistance to high resistance as they heat up due to
current flow. They are normally used to protect circuits, but in this case
might come in handy to cut the supply to the ignition if they are left
unbypassed. As Pat mentioned for the slow blow fuses, the correct rating
ptc device would have to be found to match your ignition and perhaps be
sized a bit higher due to the heat that might already be present due to a
warm engine compartment. They'd take a bit longer to "open up" if the
engine were cold. At least you wouldn't have to replace it and you could
actually test it or forget to bypass it without damage.
At 10:42 AM 4/7/05 -0500, Pat Horne wrote:
>You can get slow blow fuses at any electronics parts house, Radio Shack,
>Mouser, Digi-Key, etc. They come in boxes of 5. I would guess that the
>fuse should be in the 1~2 Amp range, so you would want to get 3AG1SB or
>3AG2SB fuses. Slow blow fuses are rated to take surges better than fast
>blow fuses. As I recall the slow blow fuses will take a 100% overload for
>something like 1 minute before it blows. The fuse rating will depend on
>what ignition you are running. Factory coil will take a smaller fuse than
>a hot coil. If you decide to try it please let us know what fuse you find
>Oh, be sure to have a spare fuse so you can reset the system just in case
>it gets activated! The fuse is not needed to drive your car, just arm the
>Hall, Phillip wrote:
>>Hey Pat -
>>I like your idea. Could you provide the particulars to this idea, i.e.
>>where to get a slow blow fuse.
>>Richard - sorry about the truck - real bummer.
>>[mailto:email@example.com] On Behalf Of Pat Horne
>>Sent: Thursday, April 07, 2005 8:58 AM
>>Subject: Re: Theft Protection
>>Most anyone who steals one of our cars is probably out for a joy ride. In
>>that case they don't want attention called to themselves.
>>When I get my67.5 back into the shop for a rebuild I plan on adding a slow
>>blow fuse in series with the coil power lead, and a switch to bypass it. The
>>value of the fuse would be such that it would allow the car to start
>>normally, and drive for about 30 seconds before power to the ignition is
>>cut. Now the thief is sitting in the middle of the road, with traffic
>>building behind him. It is my belief that he won't try to figure out what
>>the problem is, and just abandon the car.
>>As for what to do for the bypass switch, car thieves will be on the lookout
>>for anything that looks like a kill switch, so why not put it in plain
>>sight! I've seen quite a few older cars where the owner installed a
>>headphone jack under the dash. I plan on installing such a jack with the
>>plug that is inserted into to jack being the bypass for the fuse. It's
>>hard to find the switch when it is in your pocket, away from the car!