The AGU1070 main relay has an internal diode from terminal 86 pointed towards the relay coil. Check your S57 diagrams and you'll see what I mean.

This relay is NLA from Jaguar. I can't find an exact replacement though, from memory, it seems like both Bosch and Hella offered one a few years ago. Anyway.....

What vendors are selling now is a Bosch 0 986 AH0 602 which has an internal diode after the relay coil and pointed towards terminal 85. (see pic)

I am presuming the diode, in this case, is to block voltage spikes.

Will the different diode location jeopardize this protection? I'm having a hard time wrapping my head around this for some reason.

Cheers and thanks
Doug

 

Think of a diode as an electrical check valve. When the + voltage is on the base of the triangle (anode) and - on the other end (cathode) the diode will turn on and allow current to flow.

Diodes are used in coils to suppress spikes caused when the coil turns off just like an ignition coil. You could easily add an external diode that will do the same job a 1N4001 or 1N4002 would be suitable for most relays.

 

Yes, I know


I have a slew of those diodes (although I can't remember why!) and considered installing one externally as you suggest.

However, would the relay shown, with the diode position on the other side of the relay coil (versus original design) work OK?

Cheers and thanks
Doug

 

Yes, it does not matter where you put the diode as long as the polarity is correct.

If the polarity is swapped, so for the relay in the pic if you put positive on pin 85 and negative on pin 86 the relay would not turn on.

 

I'm not too good at this stuff but I have a Delcity catalog. If the diode diagram arrow points to 86, the 85 is negative. That's Delcity item 73986. If the diode points to 85, the 85 is positive. That's Delcity 73990.

I have the replacement you photographed on two of my cars and they run fine and have yet to catch fire

 

Doug
Is this one the correct exactly the same diode configuration as OEM replacement, please?
https://www.delcity.net/store/Relays...73578.h_801565

Also google says XKs unlimited have them, and motorcars ltd.
http://www.motorcarsltd.com/33393.html
Greg

 

I almost get it. Enough to follow, but not create it!


My lump's starter relay has diodes on two of it's legs. Which, I'm unsure
about. It came that way with my conversion kit. To prevent a back feed.


For a bit, I hooked the starter with a relay and no diodes. It seemed to work. but, issues arose, which I attribute to back feed.


Back to the original relay and harness with the diodes and all was well, again.


Carl

 

According to the spec sheet, no, it isn't.

The original has terminal configuration of 30-85-86-87-87. The one you linked has the more common 30-85-86-87-87A configuration. Plus the diode location is (in yet another) different location. However, it looks to be an exact replacement for the "feedback inhibit" relay...which is a misnomer, IMO....and a different conversation


I saw that but without a pic of the diagram I wasn't sure what I'd be getting.

Cheers
DD

 

I just did the same and no fires ....or even wisps of smoke escaping

Cheers
DD

 

It will not work as a direct plug replacement due to the polarity (pins 85 & 85) being reversed. If you plugged this relay in the diode would turn on partly bypassing current from the coil, the relay may or may not turn on.

If you reversed the Pos and Neg wires in the relay socket it will work.

The diode in this location works slightly differently that the blocking diode in Dougs post, when This relay turns off the diode conducts and recirculates the spike through the coi. In the other relay when it turns off the diode turns off and prevents the spike.