[TR] TR2-3 electrical melt downs

DAVID MASSEY dave1massey at cs.com
Thu Jun 25 05:35:33 MDT 2020

 Since I am an EE type person, I redesigned a portion of the wire harness.  All the switched power circuits are powered through a relay (with the sole exception of the coil) and there are 9@ polyfuses ( solid state device that acts like a self-resetting fuse) for all of the switched loads.  This includes the addition of two convenience outlets (one switched and one unswitched), cruise control and an electric fuel pump.
I also the more common addition of an electric fan and relays for the high and low beams.  And these heavy loads disengage whenever the starter is engaged.  A cool trick used on the TR8.

I also know the bane of service people everywhere is undocumented changes.  Especially wiring changes.  So, I have also provided a wiring diagram of what I have done (attached).
But then, I wasn't ham-strung by an accounting department.  My hat's off to the clever designers who did as well as they did given the budget they were given.
Cheers, y'all.

-----Original Message-----
From: John Macartney <John.Macartney at Ukpips.org.uk>
To: bill beecher <notakitcar at yahoo.com>
Cc: DAVID MASSEY <dave1massey at cs.com>; triumphs at autox.team.net <triumphs at autox.team.net>; fot at autox.team.net <fot at autox.team.net>
Sent: Wed, Jun 24, 2020 10:52 am
Subject: Re: [TR] TR2-3 electrical melt downs

I think Dave Massey is spot on in highlighting the things that can go wrong with old looms. He’s also correct in saying the cars were built to a budget and I’d add they were never built to last as long as so many have. Ten years was the engineered life expectancy. Dave is also prudent to comment on the very limited number of fuses for the US market. However, it’s worth pointing out that in the days of yore, cars bound for Italy and Sweden had completely different looms. IIRC, Italy spec cars had 12 main fuses and Sweden a few less. Sweden also banned the plating that was used on all hardware and fasteners and insisted on another form of plating. Trouble is, I can’t remember what it was now. So, if you’re planning on a new loom, get one made in Italy to original spec. Magneti Marelli used to have a subsidiary that made them.

At the Battle of Waterloo, 1815:Lord Uxbridge:  “By God, Sir - I’ve lost my leg”Duke of Wellington: “By God, Sir - so you have!”

On 24 Jun 2020, at 15:52, bill beecher <notakitcar at yahoo.com> wrote:

I counted, I only have two(2) fuses on my ‘58 TR3.   Where might the other be?Thx,Bill BTS30800L

Serenity Now......
On Jun 24, 2020, at 9:38 AM, DAVID MASSEY <dave1massey at cs.com> wrote:

 Keep in mind that these wire harnesses, like the car as a whole, was designed to a budget.  These harnesses had three (count 'em, 3) fuses.  As such some items were unfused like the headlamps and the coil.  And those things that are fused shared a fuse so the fuse had to be sized to carry the current for everything on that circuit.  But the wires were sized for the particular load.  A thinner wire will have a nigher resistance and under  short-circuit conditions the current can be limited to a level that will not blow the fuse but the current will cause enough heating to cause the insulation to melt.
Another factor against us is the age of the harness.  The connector contacts get corroded and will get hot under normal circumstances.  Wire strands can fatigue and break within the insulation again resulting in overheating under normal use.  The insulation gets stiff and cracks exposing the wires within.  Lots of potential failure modes here.  

Compare this design to those found in modern cars you will see dozens of fuses.  Sure there are a lot more electrical items but most things have their own fuses.  This means you can size the fuse more appropriately for the wire used to power that device.  Also the connectors used are water tight and don't corrode as quickly.  Also, they are, on the whole, a lot younger and therefore retain more of their original integrety.
But a fresh works well enough so if you fear a melt-down a new harness may be a good investment.

-----Original Message-----
From: bill beecher <notakitcar at yahoo.com>
To: Tom Householder <trhouse at columbus.rr.com>
Cc: Triumphs at Autox.team.net daily digest <triumphs at autox.team.net>; FOT List <fot at autox.team.net>
Sent: Tue, Jun 23, 2020 8:52 am
Subject: Re: [TR] TR2-3 electrical melt downs

Have a friend with a TR6 that had a significant meltdown behind the dash.  I should think, given the right set of weaknesses, most any section could melt. 
Bill B

Serenity Now......

On Jun 23, 2020, at 4:52 AM, Tom Householder <trhouse at columbus.rr.com> wrote:

Over the years I have experienced and seen harness melt down in the looms to the tail lights .. anyone ever had an under dash melt down?

Trying to answer a question asked of me. 

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