ID relays on bulkhead

Hello could a member identify the 5 small relays located on the left hand bulkhead of the engine bay in a 94 XJ12. Thank you

The only information I have on those relays on a 94 XJ12 is in the JDHD CD JHM1130 which shows relay locations on a RHD car - but only four relays on that bulkhead.
From the right in your picture -
Green base = A/C clutch
Black base = Fuel Injection Main
Yellow base = Oxy Sensor heater
Red base = Air Injection

That fifth relay appears to be in a white base and could be an add-on for which I have no information.

Try pulling it to see what stops working! :slight_smile:

Thanks for that information Bryan. That fifth relay does have a white base and is original to the car wiring loom although the relay itself is not oe. What is the large metal rectangular box between relay 3 and 4 for?

Sorry, don’t know - hopefully someone with a V12 will know

Here is some info I have saved, no doubt for the XJ40 AJ6 (6 cylinder) models. Hopefully there is enough kinship to the 12 cylinder models to be of help. Sorry I didn’t record the original source:
'93 / '94 cars with SIX relays on the firewall are served thus:
Black base = EMS fuel injection main relay
Green base = A/C clutch relay
Yellow base = Oxygen Sensor Heater relay
Purple (Lilac?) base = Auto Transmission power relay
Blue base = Engine Breather Heater relay
Red base = Air Injection Pump relay
[If there is a SEVENTH relay it is the 'Ignition ‘ON’ relay in a white base]

If you have the Hella blue relays in any of these slots, replace them with sealed aftermarket units. Jaguar suggests replacing those Hella relays.

I thought that one of those relays would be for the transmission. Any idea where it is located?

The only relay associated with the transmission in the 94 XJ12 circuit diagrams is the high-mounted stop light relay module L in the front right side of the trunk.
Is that the one you mean?

No I’d read that the transmission on this model had a relay associated with it that if faulty could cause the transmission warning light to illuminate.

I had a look in the trunk and found the transmission control module and a
light blue relay for the fuel pump on a blue base. Just behind it is a black base but no relay fitted. Should there be one?

So is your tranny light on? What exactly is the problem? - or are you just curious to identify the relays?

Is that photo of the right rear corner of the trunk (just ahead of the tail light) or the right front corner of the trunk?

Looks like the right front - you can just see the antenna

Bryan it’s the right front corner of the trunk. I was able to solve a non start problem by swapping one of the relay’s from the front of the car to the fuel pump location. I’m not sure if I need to find a relay with both a resistor and diode for this location. I was initially looking to solve the non start issue by replacing the engine crank sensor and/or the flywheel sensor but both sensors showed a resistance value so I thought they might still be good.
Abercanadian I’m looking around this area as I’m also trying to solve the problem of a transmission warning light that comes on after about a mile of driving which seems to cause shifts to become a little more harsh than they were before the light comes on, it doesn’t cause the transmission to go into a ‘limp home mode’. After reading a post it seems that sometimes a warning light can be tripped because of a problem with the air injection system which doesn’t result in a LHM?

That’s right that’s the side of the antenna.

A picture with the blue relay moved and you can see the black base of a connector behind it.

According to the circuit diagrams for the 94 V12 (the only things I have to refer to these days!), in that position in your photograph there are two Relay Modules - “L” in a black base and “K” in a blue base, serving the following:-

L1 = High mounted stop light
L2 = Trunk release
L3 = Left headlight flash (secirity system)
L4 = Fuel pump #2
[Fuel pump #1 is served by the relay in the right rear corner of the trunk]

K1 = Heated rear window
K2 = Antenna UP
K3 = Antenna DOWN

Does that make any sense?

Hi Bryan thanks to LyonsJags I now have the 94 circuit diagram for the US market. However this vehicle is a UK version so there might be some differences to the wiring and colours?. I took another picture of the rear most relay position in the right rear corner.

It has a black base and wires Blue/red, Brown/yellow, blue, black

While the relay on the blue base has wires Brown/yellow, Brown/yellow, green/red, yellow/blue

These don’t quite match up with the diagram

The black base without a relay has the wiring Brown/purple, Green/blue, green/orange, black

Those are the correct wire colours for the #1 fuel pump relay in the rear RH position in the trunk according to the wiring diagram I have for a 94 V12.

At the moment I can’t see any relay base with the other wire colour combinations you quote.

That’s very strange as I didn’t change that rear most relay to solve the non starting problem I had, instead I swapped the relay on the blue base above the aerial motor with one from the engine bay and the engine started immediately. I swapped them back to check that was the cause and the engine wouldn’t start.

OK, I know when I am defeated! :frowning:

I’ve searched the wiring diagrams in an attempt to find a relay in the trunk or elsewhere with that wiring colour combination and I can’t see one.

Must be something unusual about your car.