Diode relay for fuel pump

Hi Mark,

The DAC 1861 is not a relay, as Frank says and as mentioned in the thread, but a diode pack and can’t be substituted with a relay.

I have one, removed from working car, I checked the diodes and they are all good.
I am in France, if you are interested send me a PM.

Thanks - I’m aware it’s not a relay and thanks for confirming it might be possible to create something from a relay with the right components for a few pence. The car in question is a friends and he got it from someone who had replaced the diode pack with a relay and then spent weeks wondering why the car still wouldn’t start!!!

The car is a 1990 4.2 V8 Range Rover - would ’ jumpwiring fuel relay white to white/green’ apply? - a long shot asking you as it’s a different car but maybe the loom has commonalities.

Thanks again

Hi - I can’t seem to PM you?

If you search on eBay for “Jaguar Pektron red” you will find two DAC1861s listed for sale.
I have no affiliation with either eBay seller, just wanted to point out that there are two of them for sale on eBay today.


Yes, easy enough.

Aristides’ pictures shows more than words can express, Mark…:slight_smile:

I don’t know if the Range Rover and Jaguar set-ups here were identical, nor if their colour coding were at the time. A look at the wires at the fuel pump may clarify.

I assumed we were talking Jaguar. But if there are a white and a white/green at the fuel relay; it’s likely a valid advice - to be tested. It’s easily reversed if the proper part is sourced or made up…

xj6 85 Sov Europe (UK/NZ)

Many thanks

Hi - I received notification of your PM via email and replied via email. It seems the messaging feature via the forum isn’t available to me. Is this a premium feature? The ‘how to’ guide mentions icons that I just don’t see.

Please le me know if you got my email reply.


Did you tap on the posters avatar?
This should come up;

Hi can a fuel pump relay replacement work as a diode … I’m at a stand. Still on this one it failed on my car this diode what would be the nearest to a replacement… can AGU1068 work … that’s replacement for dac1861…… diode

Not directly, David - the diode pack is very special…

It is meant to connect different inputs to operate without ‘backflow’ - it could maybe be replaced by several relays. However, the diodes, if faulty can be individually replaced…

The function of the diode pack is related to a back-up safety feature; it prevents the fuel pump to run with ign ‘on’ if the engine is not turning. ‘Jumping’ the fuel relay will run the pump in ‘run’ and ‘crank’…

What are your specific symptoms…?

xj6 85 Sov Europe (UK/NZ)


Hi Frank, very good Sunday evening … my issues are this diode , I am going to try can you bypass it with a relay modification by my auto electrician……

you probably want to start a new thread for your fault and not add something random to someone else’s thread. The example you are quoting above is from a diode pack used as part of the charging circuit for an alternator and the little red box talked about in posts14-20 is about combining two voltages without one contaminating another, e.g. running a fuel pump when the engine cranks and then also running it when the engine is already running.

Rather than quoting part numbers (and different cars use the same part numbers for different things), start by simply explaining where and what your fault is.

kind regards

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Mark I got it tested the diode by my auto electrician , it’s failed I’m just wondering can you bypass it I will look … this is definitely my issue I’ve spent a year on the car … I’m convinced…… anyway I think for certain this relay can work … AUG1068… fuel cut switch also its a Bosch unit ……

Better then bypassing it so I’m gonna try that … when it arrives

[quote="Davidbrien6484jag, post:32, Hi Frank, very good Sunday evenin356592, full_true_]g … my issues are this diode , I am going to try can you bypass it with a relay modification by my auto electrician……

It’s not clear which diode you are referring to, David - there are 3 in the pack…

One is for the main relay, engaged with ign ‘on’ and ‘crank’ - white and black wires on relay, and two whites on relay pack.

Two diodes for fuel relay; one white/yellow ‘in’ at diode pack, for engaging fuel relay in ‘crank’. One diode pink/blue wire ‘in’ to diode pack from reed switch in AFM - powered when engine is running. Both are connected to fuel relay by single white/purple wire to fuel relay…

To avoid ‘backfeed/contamination’ as Marek mention; one relay is required for each failed diode - 3 relays for all. But a diode failure causing failure of the fuel relay to start is simply to jumpwire fuel relay as described. This is basically harmless. If the main relay diode fails it is fair enough to use a relay there. Which is why I asked for symptoms…

Auto electricians are sort of magicians. While installing relay(s) is fair enough ; the simpler procedure is to open the diode pack and replace the failed diode(s)…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

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Attached are some pictures that add details to Frank’s comments including the schematics from the XJ6 S57 Electrical Guide and some pictures that I took a while ago of a DAC1861 Diode Pack from one of my three XJ6 parts cars. I agree with Frank that the best way to solve this problem is to remove any failed diodes from the Diode Pack and replace them with the correct diode(s). This could be a Do-It-Yourself job given the simplicity of the Diode Pack, but certainly within the realm of an experienced automotive electrician.



I’m onto ken Jenkins about it , according to my auto electrician all 3 failed… I got to the bottom of the old XJ6 issue after a year…… Thanks Paul re frank ….

Frank, I appreciate your kind gesture…. I’ve gotten to the problem. Now i go get it sorted … took me a year… I’m. A bit overwhelmed from it all……

Most unusual for all diodes to fail simultaneously, David - but s… happens…:slight_smile:

Failing to connect at all is certainly debilitating, instantly noticeable - but ‘bidirectional’ failure may not be noticed; the resultant feedback may not be pronounced enough…

xj6 85 Sov Europe (UK/NZ)

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