> Here is what I noticed. I replaced the existing SFE 20 amp buss
> fuse with an AGC 20 amp buss fuse. Is there a difference between
> a SFE and an AGC fuse?
Nothing worth worrying about. The AGC is rated for operation at 250v max,
while the SFE is only good for 30v; either one is fine for automotive use.
However, other sizes of SFE fuse (like the 15 amp that Dan recommended) are
different physical sizes and hence don't fit the TR fuse holders. Only the
SFE-20 is (almost) the right physical size.
> As the fuse blew, I felt it, caressing it
> into death as it saved my car's wiring. The metal end toward the
> front of the TR6 was hot; the rest of the fuse was not. It took
> only 2-3 seconds to blow.
>
> With this limited information, any hints? As I replaced the fuse
> my car was turned off and all lights were turned off. Any
> troubleshooting ideas?
I believe you have two problems, the unexplained current drain and also a
bad contact in the fuse holder (where it got hot).
First, get a copy of Dan's book !
To find the current drain, use some clip leads ($8/set at Radio Shack,
"jumper wires with alligator clips") to connect a test lamp across the fuse
block terminals. The test lamp will light and stay lit until you disconnect
the load. Now work your way around the car disconnecting the various things
that run off the purple circuit : horn relay, hazard flasher, trunk and
tunnel lamp, etc. (I don't have a diagram for a 74 handy, it may be
different than the 72 diagram I'm looking at.) If the test lamp still
doesn't go out, it must be a short in a purple wire. Jiggle and poke at
anywhere you can see a purple wire, hopefully you'll make the test lamp
flash and know you're near the problem.
Another technique that sometimes works is to use a magnetic compass as a
current detector. If you get it near a wire carrying current, the needle
will turn and align with the wire. It helps to use a higher current lamp to
bridge the fuse block, like an old headlight bulb (I save them just for
things like this, as usually only the low beam filament burns out). It
draws enough current that sometimes you can find the short just by feeling
for where the wire is warm.
I'm a bit surprised that Dan recommended a 15 amp fuse in the feed to the
horns ... do TR6 horns really draw that little ? At something like 8 amps
for the hazard flashers, that would only leave 7 amps for both horns (even
without any margin against nuisance blowing). Each horn draws that much on
a TR3!
Randall
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