XK 120 horn contact getting hot?

XK
#1

Hello Folks,
One of my original horns wasn’t working so I took it apart and adjusted the contacts as outlined in the manual. Now it works but the contacts get very hot and start to smoke. I took apart a later horn, not sure which model it came out of, and found that the coil was burned to a crisp. It had an electrical component in series with the coil. It shows in one of the pictures. Does anyone know what this component does? Perhaps to keep the contacts from burning out?
Thanks

Wes Keyes
York, Maine

later horn with burned coil.
later horn with burned coil.2448×2448 1.39 MB
XK 120 horn, contacts get very hot
XK 120 horn, contacts get very hot2448×2448 1.2 MB

#2

Which model horn is that? Mine have no such black box component.

IMG_20200603_164048894
IMG_20200603_1640488941060×596 80.9 KB

Those horns draw a fair amount of current, which is why they need a relay. A wire getting hot and smoking suggests high resistance, small contact area, in other words, dirty contact or not tight, though perhaps you already knew that.
I wonder if that box is a resistor?

#3

Hi Rob,
I don’t know which car the horn with the unknown component came out of. There are no numbers I could find on the housing.

Wes

#4

Hello Wes,
according to a Lucas Technical Service document there are two different types of Windtone Horns. The earlier type WT614 was replaced by the later type WT618. The early one was equipped with a pellet type resistance to damp excessive sparking which would occur at the contacts during rapid make and break. At the later one the terminal block was made of resistive material which does away with the pellet type resistance. So I think, your first picture shows a WT614 horn with the 8 Ohm pellet type resistance. The second picture shows a WT618.
Joerg

#5

Joerg1,
Thanks for the detailed reply. That is very interesting. Say where did you get the technical service document? Are they available to buy or download?
Wes Keyes
York, Maine

#6

Wes,
I found it here: https://mgaguru.com/mgtech/books/lts_otcc.htm. It is in session 8.
Joerg

#7

Wes,

The “Lucas Technical Course” provides an introduction on this feature. See here. Hope it is readable.

Bob K.

image

#8

Thanks again folks for the great detail and info.

Wes