Diode relay for fuel pump

Looking for a used or new fuel pump relay for 85 jag,xh6,4.2lit.best price I’ve seen is 175.00 canadian.this is a pektron diode relay ,5 prong. This seems awful expensive.any help is appreciated.

Sure about the diode requirement? Many have swapped in 30 or 40 amp Bosch tyoe relays of various genre.

If there is a need for a diode to prevent a back feed, it seems feasible to solder one in on the correct leg. My guess would be the trigger side rto the ignition switch. ,

Under 25 bucks ought to do it and that is generous…


Frankly, any old automotive relay will do. All that is “special” is that there is a diode across the pump. A simple 1n4003 will do, with the band on the +ive (pump) feed and the other end on (pump) earth.

Five bucks or less is realistic.

kind regards

My relay is a pektron 5 prong relay. (175.00) I’ve tried other relays (new) and it doesn’t work.this is the red diode unit on firewall that communicates with other relay next to it.

I’m unclear what stan1 is referring to. There are 2 AGU1068 silver Bosch fuel relays and 1 DAC1861 red Pektron diode module. The Pektron module looks like a plug-in relay, but isn’t. I haven’t taken one apart. From the schematic, it’s just 3 rectifier diodes (essentially an OR-gate to power a fuel relay from different sources) and a resistor to protect the ECU.

For $175CAD, I would triple check that the existing unit is failed. There is only $2 worth of parts inside; it should be repairable. I may open mine up just to see what’s inside.


You hit it right on.there are four rectifires on this one.the solder was split on one of rectifies going to another…i re_soldered but still no go.not sure what to do?

OK, now I understand.

Four rectifiers sounds strange. Oh well. Troubleshooting is just probing each component with a multimeter looking for opens or shorts (both polarities of course). The resistor is going to be a small value, so use a low scale on that one. Lastly, make sure the “relay” pins are free of corrosion. You should expect to find one failing component in something this simple.

I’ll open mine up this afternoon and have a look around.


It isn’t a relay then. It simply sits in the same housing as a relay.

For the diodes, you should see continuity one way but not the other when tested with a meter. For the resistor, you can measure that directly, for the transistor (if it has one) then that should behave like two diodes together - the interweb can describe how to measure and diagnose that. Five dollars will be more than enough - the components are literally 5c each.

Post a photo of both sides of it and any writing on the components and all will be clear.

kind regards

I put pos and neg to 3 and5.with test light,i got power to #4only.nothing to #2 which is my pink/white wires.let me no if you got pictures?

If I have managed to make sense of the pictures, I make that:-
1/ a diode goes from pin1 to pin4
2/ a diode goes from pin3 to pin5
3/ diode goes from pin2 to pin5 (but going through a resistor on the way)

(I make the bands on the diodes are on pins 4,5 and 5 respectively)

Accordingly, if your meter has a diode setting, for 1/ I’d expect it to read something
with the red lead on pin1 and the black lead on pin4 but not the other way around; for 2/ I’d expect it to read something with the red lead on pin3 and the black lead on pin5 but not the other way around; for 3/ I’d expect it to read something with the red lead on pin2 and the black lead on pin5 but not the other way around;

If your meter only has ohms, then set it to the biggest ohm setting and expect to see it briefly blip from pin1 to pin4 but not register at all the other way around. Similarly for the others.

The diodes look like 1n4001’s or similar. All of the 1n400x series are the same except that the amount of current they can handle goes up with the number, so feel free to use a 1n4003 instead of a 1n4001 but not the other way around.

If this is connected to the fuel pump and the fuel pump pulled too much current, then one of the diodes may have failed and thus left your fuel pump always disconnected. If that were so, then the real question to ask is why did your pump draw that much current? That is the real problem to fix and this is just the collateral damage which has temporarily saved your pump…

kind regards

This “relay” could be replaced with the 40amp (I know it is overkill) $5. plug-in relays that you get at truck parts centers. These things have normally open and normally closed contacts,
choose the closed ones when it is switched on.

Dear Stan,

I don’t have a circuit diagram for what this connects to, but functionally, there are two circuits here and this is what they do:-

Firstly, if there is a voltage coming in on pin 1, then it goes on to pin 4. However, if there is a voltage on pin 4, then it can’t go back to pin 1.

Similarly, if there is voltage on either (or both) pin 2 or pin 3, then it gets sent on to pin 5. Any voltage on pin 5 cannot go back to contaminate or influence pin 2 or pin 3, so pin 2 is kept isolated from pin 3. Additionally, the voltage coming in on pin 2 is taken down a peg by the resistor before it goes on to pin 5.

(Each diode drops the voltage by ~0.7volts (that’s just how they work), so if the pin1 voltage is lower than 0.7volts, nothing gets through anyway. If pin1 has 12volts on it, then pin4 will get 11.3volts.)

kind regards

Stan, Not a relay! These little diodes direct current for the start circuit (before firing) and the run circuit. They are too small to take pump load current so - I suspect - work through a contact type relay. If you trace the circuit out make sure that you can “see” only two ends or terminals for measurement - then you can reliably measure the component. If not you must unsweat one end to permit same. They are regular silicon diodes so a multimeter will measure “resistance” of low value in one direction (in circuit voltage drop will be 0.6v) and infinite resistance in the other. You should be able to identify faulty item in this way and replace it at Radio Shack or similar for a matter of cents. Regards, Paul

The maximum forward current is 1amp. The peak inverse voltage increases, with 1N4007 being the highest at 1000 volts. Price is cheap–no reason to use anything but 1N4007s.

I took mine apart. It’s identical to stan1’s. Here is my reverse-engineered schematic of the module with both Pektron pin numbers and the standard relay equivalents. It jibes with the Jaguar schematic. I checked the components under the microscope; the diodes are marked 1N4006.



1 Like

Thx rob.i took my relay into electric technician and sure enough it took a pooper.ordered new bosch ( cheap).i will fillow up when i get a new one .i thank everybody for helping me out.

After the fact, Stan; the Pectron diode pack connects two’trigger’ sources to the fuel relay proper - and the diodes prevents undesired fuel relay operation. The fuel relay is triggered by the white/yellow wire in ‘crank’, and by a reed switch in the AFM while the enmgine is running. The two are conjoined at the Pectron, and the diodes prevents confusion…

Another diode in the pack prevents backfeed to the main relay…

As said by others; the red Pectron is not a relay, and cannot be replaced by one. You do not mention fault symptoms - they are not dissimilar for the Pectron and the actual fuel relay, but faults require different actions… so…?

xj6 85 Sov Europe (UK/NZ)

What was the part no. for the new Bosch part.

Hi - an old thread but still valid. I need a DAC1861. The old diode pack was discarded by the previous owner so can’t be repaired!! The relay fitted in its place is obviously no good. Can a relay be modified by adding in the diode and the fuse resistor? Are there any other alternatives to the DAC1861 part as these are not easy to source.

The diode pack is not(!) a relay, Mark - and cannot be replaced by one. Basically, it has 3 blocking diodes to connect 3 circuits to operate the fuel relay without power backfeed. It is a safety feature; the fuel pump will not run with ignition ‘on’ unless the engine is turning. You can bypass this safety feature by jumpwiring fuel relay white to white/green. Which will be harmless in most circumstances - and will run the engine while you muse on solutions…

The original diode pack is a simple devise - and is usually repairable. Without the (defective) original; having suitable relay base you can likely remove the relay innards and do some soldering of diodes etc. With proper parts it should work…

xj6 85 Sov Europe (UK/NZ)