Diodes & Relays Oh My
 

my horn relay is pretty plain but noticed on a wrecked 1979 Series 2 that it had a additional diode (which I thought was a lighting thing normally) latched in via green wire then on to the main cables.

see images. just curious if anyone knows why?

https://cimg2.ibsrv.net/gimg/www.jag...390e2e9536.jpg

from the 79 model Series 2


https://cimg3.ibsrv.net/gimg/www.jag...088e9ff341.jpg

from my 1974 series 2

The red one looks like it might be a cooling fan relay.

A horn relay wouldn't typically need a diode but cooling fan circuits often have one

Cheers
DD

as it was located close to the fan/radiator that sounds about right then.
just seemed odd when i first saw it and couldn't figure.

The diode sends power to the fans when the air con is turned on, it over rides the water temp sender that turns on the fans therefore when the air con is on the fans run all the time.(in my case anyway) And it stops the fans feeding 12 volts back to the compressor when the fans are activated by the water temp sender.
Basic explanation I know, but it makes sense to me.


https://cimg1.ibsrv.net/gimg/www.jag...19b594b40e.jpg

Diodes, interesting little guys. A one way valve for volts, so to speak.


So, an e fan is a SD motor. Reverse the rotation and it becomes a generator!!! So, if the air flow causes the fan blades to turn in reverse, volts are created and flow to where they might not be wanted. A version of 'back feed". I knw enough about electriclkery to confuse myself...


A pair are built into the load legs of my lump's starter relay, Not sure why, but their absence can wreak havoc.... don't ask...


Carl


Carl