Why Fuse Box melt down

[RedBird64]

Hi Guys,

I'm new to the Z world, but not new to classic autos and wrenching on them. I keep hearing "buzz" about the early gen cars having problems with the fuse boxes over-heating. Why is this? In particular, I hear the headlights are big culprits? Why? They are only 10As!

I have a 67 Etype with 50A fuses and have had one issue in 38 years.

So what's the skinny?

Edited June 5, 2012 by RedBird64

[zKars]

Heat created by corrosion on the contacts, both in the fuse box and in the switches. Nothing magical, just lack of moisture seals pretty much everywhere.

[RedBird64]

Heat created by corrosion on the contacts, both in the fuse box and in the switches. Nothing magical, just lack of moisture seals pretty much everywhere.

Hi

Thanks for the comments and agree wih repsect to the build up of corrosion. I guess I was looking for something more "magical", as I own two other classisc (well over 30 years each) with these early style fuse boxes and always did the maintenance in keeping those contacts clean. I was looking for more of a flaw, so, no big deal in that respect. I do see an issue with regards to how the headlight column stalk is wired and how the circuitry allows for high AMPS to ground in completing the ckt. That can use some improvement.

Happy Motoring today!

Edited June 5, 2012 by RedBird64

[Wade Nelson]

Plain and simple, your Jaguar was mis-wired at the factory. You do NOT install a 50A fuse to protect five 10 amp circuits all wired in parallel.

What happens on the Jag is the 10A headlight circuit shorts out, pulls 30-40 amps, lights the cloth covered wiring loom on fire, melts a WHOLE BUNCH of other wires, and the Fuse sits there going "No big deal!"

I speak as a former 67 XKE owner.

Unless you PREFER for your wiring to protect your fuses, it's time to find a master electrician and start rewiring it with proper protection for individual circuits.

[BoldUlysses]

Hi

Thanks for the comments and agree wih repsect to the build up of corrosion. I guess I was looking for something more "magical", as I own two other classisc (well over 30 years each) with these early style fuse boxes and always did the maintenance in keeping those contacts clean. I was looking for more of a flaw, so, no big deal in that respect. I do see an issue with regards to how the headlight column stalk is wired and how the circuitry allows for high AMPS to ground in completing the ckt. That can use some improvement.

Happy Motoring today!

You'd be the first actually looking for something "magical," haha; most DIYers are interested in more concrete reasons why things do what they do.

I recently had a fusebox meltdown:

http://www.classiczcars.com/forums/thread45945.html

and after sanding and cleaning the contacts, everything is okay. It's not a permanent solution, though—I do plan to go with the far-superior MSA blade fuse box eventually.

[RedBird64]

Plain and simple, your Jaguar was mis-wired at the factory. You do NOT install a 50A fuse to protect five 10 amp circuits all wired in parallel.

What happens on the Jag is the 10A headlight circuit shorts out, pulls 30-40 amps, lights the cloth covered wiring loom on fire, melts a WHOLE BUNCH of other wires, and the Fuse sits there going "No big deal!"

I speak as a former 67 XKE owner.

Unless you PREFER for your wiring to protect your fuses, it's time to find a master electrician and start rewiring it with proper protection for individual circuits.

Hi Wade,

Thanks for your enlightening comments. I'm not sure where you were going with your reply:

"your Jaguar was mis-wired at the factory. You do NOT install a 50A fuse to protect five 10 amp circuits all wired in parallel."

I'll have to say, "I agree"! What Lucas engineer would do that? Thanks for the chuckle at your enthusiastic reply. BTW, I've never had the failure you so saliently used as an example, nor did I imply in making my reply.

My comment, " I have a 67 Etype with 50A fuses and have had one issue in 38 years". I do see I was incorrect, in that, I should have stated "50A fuse", as in singular. Sorry to have miss-led you Wade. My Jag is a factory correct '67 Etype 2+2 with me becoming the 2nd owner in '70. It has "one" 50A fuse, seven 35A fuses, and the remaining three are 15s and one 5A. My one failure was early on, wherein, corrosion began in the horn ckt.,a fused...."50A" Now, you can take off with that!

However more importantly and for the larger audience here, I think you either missed my point, or perhaps, I was not clear enough.

My point: My Jag (and my early 65 mustang cvt for this matter) has with the same type and style of fuses as these Z cars, there is a corrosion that takes place, wherein, the fuse ends rest in the fuse holder. Due to any number of environmental reasons, corrosion will gradually build creating more resistance as you stated. This corrosion, can start but is not limited to the fuse holder. As the corrosion increases so does resistance. As resistance is increased, so, does heat and the cycle manifest until such point, enough heat is generated and melts the fuse box.

So, for the general audience, the moral of this diatribe, do the maintenance periodically by cleaning those fuse terminals and the fuse ends themselves.

Happy Motoring today!

I guess I have to finish with "I'm a current '67 Etype owner"

Edited June 5, 2012 by RedBird64
typo repair

[RedBird64]

You'd be the first actually looking for something "magical," haha; most DIYers are interested in more concrete reasons why things do what they do.

I recently had a fusebox meltdown:

http://www.classiczcars.com/forums/thread45945.html

and after sanding and cleaning the contacts, everything is okay. It's not a permanent solution, though—I do plan to go with the far-superior MSA blade fuse box eventually.

Hi

Thanks for that link. That's scary stuff going on.

Happy Motoring!

[PastorMike]

Here is the magic:

Corrosion creates Resistance,

Resistance creates a Voltage Drop,

Voltage Drop = Resistance X Current,

Watts (dissipated) = Voltage Drop X Current,

Watts Dissipated = HEAT,

HEAT = Melted Plastic

[Wade Nelson]

I may not have the exact specifics of the Jag wiring / fusing committed to memory, but as a degreed Electrical Engineer (Vanderbilt) I absolutely cringed when I saw what the idiots at Lucas had done. Not just on the XKE, but on my earlier TR-6 and TR-3.

After you replace your first scorched 12-wire bundle of cloth-covered wiring, the one that ALMOST burned your car up, you will remember this conversation, and wonder why they chose a 35A fuse for a circuit that shouldn't, under normal circumstances, pull even a third of that .

Get out your ammeter. Measure a few of 'em. (10A limit on most meters, internally fused)... decide for yourself if you want to stay with the stock fusing.

[PastorMike]

I forgot this:

Lucas = Prince Of Darkness

[PastorMike]

Wade, I loved my TR3. Once used a hemp rope in place of the fan belt to get her home. Ah, those were the days.

Mike

[Darrel]

The z fuse box uses rivets in the back of the fuse block. Corrosion will start there as well. It's not the fuse to fuse holder that causes the problem.