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Electrical fire

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TR674

TR674

Jedi Warrior
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Gents
I had an electrical fire behind the dash yesterday. The green power wire from the fan switch to the heater fan went up in smoke. The fan was on at the time, and I had just pulled into my driveway when the cabin instantly filled with smoke. Damage is limited, luckily, to a few melted sections of speaker wire and melted carpet under the heater box. I've never reached for the fire extinguisher so fast!
I recently restored the heater box and the fan motor wires were new. Could the fan switch be faulty, or did the green wire earth somewhere? I'm not electrically minded, but can someone explain to me why this should happen?
I will be taking the heater box out (again) this weekend to replace the fan motor wires. I'm not sure where to look for possible electrical faults.
Regards
Craig
 
Just out of curiosity, did the motor quietly seize up and cause the wire to overload and melt down? Check it carefully before you put it back in.
 
Paul
the fan was spinning when I turned the switch off as the smoke was pouring out from under the dash. The melted fan wire stops at the switch, which has me thinking a faulty switch? I will be able to see what condition the wiring is in inside the heater box once I get it out. I'll look fir any arcing points too.
Regards
Craig
 
Being in the middle of the process of restoring a heater box myself, I just went down to the work bench and checked my wiring harness attached to the fan. When I took the wires out of the case and removed the grommet to feed the connectors through, I must have scrapped the green wire against the sharp edge of the case. I just saw a bright shiny line of copper appear when I turned the wires all around to check them.

I may or may not have caught this when I put it back together. I'd like to think that I would have, but if I got distracted and never knew what I did taking it apart, who knows?

For obvious reasons, thanks for posting this.
 
TR674 said:
Damage is limited, luckily, to a few melted sections of speaker wire and melted carpet under the heater box.
Click to expand...

How sure are you of that statement? The only reason I ask is that I, too, have been examining old burnt wiring, and the true extent of the damage isn't apparent until you strip off the original black insulating tape. Mine goes out of view around the heater box, and is apparent again in the center console. (I had a bad radio power wire).

Since you have to pull the heater box again, take the time to do a thorough investigation.... boy, that's a job I wouldn't want to look forward to! Best of luck!
 
Kevin
I will check, thanks. The power wire to the switch looks O.K. While I have the glove box out I will stip back the insulation tape and check the group of wires for further damage. I was very surprised at the lack of warning. There was no pre hot wire smell, just instant melt down.
I drove the car to work today (with fan switch disconnected!) and no apparent problems. Hopefully as I said, it is localised to the fan wire.
Regards
Craig
 
Since the power wire to the switch is O.K., the switch is not at fault.
 
Check your fuse box;If a fuse didn't blow you may have the wrong type fuses in their.British fuses are recommended in these cars.Good luck & be careful.......Ken
 
Considering Craig is in Oz, the wrong fuse "type" shouldn't be an issue, but rating, well that could very well be - or - the heater fan wires could have been moved to bypass the fuse altogether.
 
I was wondering why a fuse didn't pop. I rang a triumph mechanic and apparently the heater fan wiring is not fused. I think I'll be installing an inline fuse while I'm fiddling with it.
Regards
Craig
 
TR674 said:
I was wondering why a fuse didn't pop. I rang a triumph mechanic and apparently the heater fan wiring is not fused. I think I'll be installing an inline fuse while I'm fiddling with it.
Regards
Craig
Click to expand...

Wrong answer, smoke screen. all the green is fused . Should be top of the fuse panel opposite the white wire.
 
DNK
now I'm concerned......I'm off to see an auto electrician.
Regards
Craig
 
Well, I'm not sure if the Spitfire fan motor and box are similar, but my fan stopped working last fall, and I dove in to fix it. What I found was the wire had fallen out of the female spade connector, which plugs into a recessed male "jack" in the fan motor. I noticed that the connector(hot) was ominously close to the chassis of the fan motor. I replaced it with an insulated spade connector. In my opinion, it sounds like your connector touched the body of the fan motor. I hope it's a simple fix.

Adam.

___________________________________________________________
1973 Triumph Spitfire.
 
Hi Craig. Based on your initial failure report it sounds like the wire gauge between your fan and the switch are under sized. It is not uncommon for an undersized wire to protect the fuse.---Fwiw--Keoke
 
Craig,

I did a 100% rewire in the Crypt Car.
I think the mechanic you called was wrong
about a green wire being not fused.

I am just about positive all the green wires are
fused. If current was getting to the fan motor
it had to move thru the fan switch. The green
wired fan switch is fused. Check and make sure
there is not a wad of tinfoil in your fuse holder
box. DPO Pedro used that trick on the Crypt Car.

During my rewire I was constantly sparking things
and blowing up fuses. I am real curious how you
got an electrical fire without a fuse blowing up.

I suspect you have some interior wire burn in the green line. I would replace that entire segment of green wire.

best luck

d
 
When looking for ignition source, here are a few things to consider. The source will be the hottest spot, which should be easy to see. This also means that anything directly above this spot will be damaged, so you can look at undamaged places and rule them out.
When looking at the wires themselves, you'll probably see multiple breaking points. Where the wire section was not the source, it may have broken, but the wire ends will be fragmented, like your wife's hair ends she complains about sometimes. At the actual ignition source, the wire will have broken, but the ends will have little round dots on the end, sort of like a soldered end. The wire will have gotten hot enough for it to form those little drops. Am guessing that you'll find a spot where the wire was pinched to ground somewhere when the box went back in.
 
Very good advice Paul. Sounds like you have first hand experience with these issues.
 
Tinster said:
Craig,

I am just about positive all the green wires are
fused. If current was getting to the fan motor
it had to move thru the fan switch.
Click to expand...

Perhaps, but not certain. Someone could easily have rewired the thing B+ directly to the fan and switching B-.
 
Thanks Paul,
sound advice. I'm with you that I have exposed the copper wire when re-installing the heater box. The wiring harness shows no signs of damage so I hope not to go down the Tinster road. Anyway, I'll know more on the weekend. I'll let you know what I did wrong........
Regards
Craig
 
It is MHO that an axillary fuse block is cheap insurance against this sort of thing.There are too many unfused circuts in all LBC's. I think that the tr6 is one of the worst offenders. Its childs play to add a block to the main power leads that come off the pos battery cable. I believe that the VTR concourse allows for this sort of safety modification....
MD(mad dog)
 
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