Eureka Wire

[iornbarb]

Hi All,
The wiring diagram in the TR7 workshop manual refers to a Eureka Wire can anyone enlighten me on where and what it is?

[Bill]

Is that the one that always shorts out, and when you find it and fix it, you exclaim, "EUREKA!!!" [:p]

Bill
1980 Persian Aqua DHC

[gordon kerr]

<font color="green">Eureka wire is a high resistance wire and can be used in place of discrete resistors.

In the case of the TR7 it is used to drop the 12V of the system to 6V at the coil. The wire is on the low tension side of the ignition system between the ignition switch and the coil. For whatever reason Triumph (and probabaly many other car manufacturers) decided to use a section of Eureka wire in the loom rather than a discrete component which of course makes it much harder to do anything about if it fails.

I have never quite understood the real purpose of using a 6V coil and having to drop the voltage rather than using a 12V coil in the first place although I assume there must be some advantage. I beleive that the systems are set up in such a way that the resistance is bypassed during start up so that at this time only the coils actually receives the full 12V which is supposed to make starting easier (bigger, fatter sparks).

But then if it works at start up why not go for 12V all the time? </font id="green">

<font color="green">Gordon
GRD 1980 Brooklands Green 2l FHC
OVC 1980 Platinum Silver 3.9l V8 FHC
Bedford, UK.
http://www.waringstowntr7s.co.uk/blogs/ ... gordonkerr</font id="green">

[rosey]

Eureka wire was developed mainly for heating elements and light bulbs, it maintains its resistance even at high temperatures, unlike normal copper wire which melts at high temperature (think about fuse wire) It's an alloy of different metals and is used in this application because it maintains it's fixed resistance per unit length. It was also called Constantin but eureka sounds better!
The problem of terminal voltage at the coil dropping when the engine was cranking was solved using the technique used in the TR7 and many other cars in the 70's, before electronic ignition was developed there weren't many ways of solving the problem which is particularly severe at low temperatures (-10C or below).
Battery technology was also not as developed and lead acid batteries suffer poor performance at low temperatures because their internal resistance rises and deliver less current for starting.
I know all this because I was an electrician and looked after some very, very big batteries (2 Tons each)during my apprenticeship.
Hope this is useful information

Dave[:)]

"Do or Do not, there is no try" - Yoda

1980 TR7 Persian Aqua Drophead.
1979 TR7V8 FHC in Pageant blue
Jaguar X Type in pillar box red!

[jclay (RIP 2018)]

When the Eureka wire burns up, you're dead in the water!

If your car starts running badly for a while and then will not start, the Eureka wire is probably gone. Check to see if you have any spark. If not, jump a wire from the positive side of the battery to the positive side of the coil. If it starts, then you know that the Eureka wire is gone.

Use a 3M Wire tap on the white wire at the ignition switch to tap in a new wire and run it through the firewall to the coil. Put a stack-on connector on the tag end of the wire and connect it to the coil. Tape off the original wire from the coil.

DO NOT CUT the white wire as it does have other functions.

Have fun, drive fast & safe, be kewl,

jclay