Its really a case of good old Joe Lucas strikes again, and ohms law
takes its tole.
The problem is that even for a relatively light current in automotive lighting
terms of 10A the contact resistance of any connection needs to be very
low (milliohms) or significant heating will occur in the contact area.
The type of fuse box contact fitted to all British Leyland cars in the
60s and 70s was really inadequate from new never mind 30 years on.
I suggest that even when new the contact resistance was rather to high
and with corrosion it gets higher, increased heating results and eventually
any spring pressure left in the contact disappears and the heat
generated is so great that the plastic melts or burns depending on the type.
The only real solution to this problem is to re wire the car using a modern
fuse box which distributes the load more sensibly, but a Lucas replacement
the original will work for a few more years I guess.
Best Regards
John Dowson
At 11:30 AM 7/1/1999 -0400, Aribert_Neumann@magna.on.ca wrote:
>
>About 3 weeks ago my 71 GT-6 lost front parking/marker lights. About a
>week later I discovered that the dash lights were out also. At this time
>the rear tail/side marker lights were still functioning. A few days ago I
>also lost tail/rear marker lights. THe car was now definitely broke enough
>to fix. Problem was fuse related. Here is the puzzlement: My Bently
>manual calls for a 35 amp fuse for all three circuits. Since only the
>running lights (no headlights, no aux. feeds) are on the center fuse, I
>derated to a 10 amp fuse (years ago) with out any problems until now. THe
>cause of my light failure was that the fuse box ( secifically the plastic
>tab that supports the clip (that the wires are crimped to) that in turn
>contacts the fuse) had MELTED and the plastic had actually flowed between
>the fuse and the clip. Since the system was spec'ed for a 35 amp fuse, why
>would it get warm enough to melt the plastic with only a 10 amp fuse. BTW,
>the 10 amp fuse is still funtional. My only guess is that the 10 amp fuse
>is defective. I scraped the melted plastic off of the clip and inserted a
>35 amp fuse (and a sliver of wood between the clip and the melted plastic
>tab to provide good electrical contact between the clip and the fuse) and
>the electical system is funtioning well. One last bit of info - my engine
>compartment is very hot - 2.5L and headers. I do not think this has
>anything to do with the melted fuse box, but a few weeks ago after being
>stuck in first gear traffic for about a 1/2 hour, I noticed a stream of
>heat entering thru the fire wall. I removed my sandal and when traffic
>sped up I searched for the cause with my bare left foot. THe source of the
>heat was a loose rubber boot on the clutch linkage and the result was a
>foot that got lightly burnt from the hot air and that was tender for the
>next hour.
>
>Speculation as to why the fuse box melted and suggestions on how to trouble
>shoot a system that appears to be ok
>
>
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