Power Distribution Help....XJ6

I am a high school shop teacher we took on a project that is turning out to be a real pain. The car is a 1973 XJ 4 door. A couple years back the owner of the car decided to ditch the original motor for a SBC and Tranny. Which the motor and tranny are easy enough to figure out, but when she did this, she took it to a shade tree type and he cut and spliced all sorts of wires. It is bad and has been a good example for my students on how not to wire a car.

I have got a ton of things figured out, but the most important part right now is figuring out the power distribution. Basically how does power get from the battery to the key switch? On the wiring diagram I have it shows a single wire leaving the battery to a junction where 14 brown wires split out. From this spot it shows a single brown wire going to the key switch. I have the key switch loose and from the key switch side I can back track a heavier brown wire a few inches to a connector, at this connector all wires change from colored plastic wrapped to a white woven cloth wrap as they enter the wiring loom. As a result I am not sure where any of them go.

Just FYI the wires on the switch are a heavier Brown. White and Yellow, Pruple and Black, Red and Brown, Smaller diameter Brown, and a White and Black.

I am assuming that the Heavier Brown is in fact the one that is supposed to receive power from the battery at the switch.

Can anyone help? Provide a picture of where the wire leaving the battery goes?

Thanks a ton!


Let’s be sure whether you have a Series 1 or a Series 2.
Here is the spotter’s guide.
Series 1 had the bumper below a large grille.
Series 2 had the bumper raised due to Federal rules, and there is a smaller upper grille above the bumper and a wide lower grille below the bumper.

By SBC I imagine you mean small block chevy. This swap was common enough in the 70s cars because there were labor and quality problems at the factory, particularly valve seats dropping out when owners allowed the cars to overheat severely. A Chevy was cheaper than a valve job. The British call this conversion a Lump and there is a Lumps discussion group here on jag-lovers.

Here are some pix of my '74 Series 2 XJ12 left hand drive, which should be similar.

Positive battery cable terminal post on the right hand firewall, brown wires attached here go up and across to starter relay.

One brown wire plugs into the starter relay, another goes over along the top of the firewall to another terminal post on the left hand side.

Here is the left hand terminal post, under a rubber cover, with the brown wire going to it.

I couldn’t get a pic inside the car, but the inside end of this terminal is where the brown wire continues to the key switch.

You do have a task, Rob…:slight_smile:

The original wiring diagram is of course useless in as far as the PO changed wire colours - but still shows where everything goes. The real problem is to find the termination points, ‘from where’ to ‘to where’ for any single wire. This is no sweat with colour coded wires - in this case your students will learn a lot about frustration, but nothing about how to handle car wiring diagrams…:slight_smile:

Swapping to a lump requires no change in the car wiring - both engines, and of course the car itself, requires the same wiring connections - on may, charitably, assume that the old wiring was changed due to wire deterioration.

The ignition switch gets power from the bulkhead interconnection point - brown is the standard Jaguar colour for constant power. The ignition switch has internal interconnections, the ‘out’ wires goes to one to the ign coil ‘+’, normally *white’ - active in ‘run’ and ‘crank’. This white wiring also runs the fuel pump and fuel tank changeover switch - in short, everything required to operate during starting or driving; but by convention, branching wires associated with white has additional colours added…white/something

White/yellow wire is only powered in ‘crank’, operating the starter relay - but the SBC may have further requirements specific for cranking/starting.

These are the essential connections to run the engine - further wiring may be fitted for various purposes, depending on market and model. With ign ‘off’ one terminal is connected to the brown - some POs connected radio to this, or anything wanted with ign ‘off’’. On some models the ‘off’ position was used for purposes not likely used for the SBC - such wires at the ign switch are redundant…

The crucial point is basically to verify which connection on the ign switch are powered in which positions - a class act…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

I can add a bit to “the wiring of a lump”.

As to the starter relay. four wires there.

  1. WY from the ignition switch to “trigger” the relay.
    2.WR out to the solenoid.
  2. Brown. Power for the load.
  3. Relay to starter interrupt on the shift tower.

And diodes on in and out. Which and the direction allowed escapes me. I do know that failure to include tthem feeds back and weird thngs happen. Don’t ask…

Caveat, I’m a bit fuzzy on 2 & 3 as above.

If need be, contact me PM and I’ll check my Jaguar Lore for clarification.


Thanks for the help so far. I am working this out a little at a time.

So here is what I know… I believe that we have a series 1. No bumper of course, but I do not see how a bumper would have fit between the head light and front turn signal.

Here is a quick Shot. On the fire wall I found 2 electrical connections. One just right of center has no brown wires at all. It has the Name Lucas 6RA number: 33222F 12V 4264 on it. There was a second similar box on the left side with No wires connected at all again: LUCAS 6 RA number 33293D 12V 1686. The second box with no connection had a more recent Relay (plastic next to it). The more recent Relay is pictured. I believe the PO disconnected the original relay and started rewiring here. I would like the easiest way to wire back to factory is possible. Here are a few pics of my findings.

Box on Right (Passenger side)

Box that was bypassed and plastic relay…

Then I also have a mess on the right side fender… Seen here:

Thanks again for all the help. Is there a good write up for wiring a lump? Something step by step that will prevent any funky issues. I hate to figure it all out on my own if there are directions already written.

Sadly the only heavier brown wire I found on the firewall was going to ground off that newer plastic relay.


  1. My first suggestion is to move your posts to the “Lump” forum.
    folks, there including me, to a fashion, have dealt with those issues. A clean mating of Jaguar and GM. It can and has been done many times.

  2. Only somewhat related, but doable and cleans up some crowding. The right valve cover can be reversed, so as to move the filler caps and PCV hose away from the crowd at the firewall.

  3. I suspect that much of that spaghetti is “dead” and does nothing.

  4. The black plastic generic relay seen hanging in space might well be the starter relay. Horribly wired, but just might work. I’d durn near bet the car will crank and fire in any of the forward gears and reverse!!

  5. The SBC is pretty!!!

  6. At this stage, .starting over might be the best course. Just make a list/plan of the needed functions and how to wire them. Example.
    A. Charge circuit.
    B. Igntion Circuit.
    C. Fuel pump circuit.
    D. Instruments.


Ok, you definitely have a Left Hand Drive Series 1, with the front turn signals above the bumper.
The Series 2 had them below the bumper. I see our Spotter’s Guide page shows only the non-Federal version of the Series 2 bumper, where the two USA-Federal collision versions had large rubber coverings. Though that doesn’t concern you here.

Here is a map of the relay locations from my Series 2 parts book.

The numbers after the labels are other page numbers in the parts book. The little dashboards with steering wheels by the ignition and wiper relays indicate left or right hand drive.

Your Lucas 6RA relays are probably the starter relay just to the right of center, and the heater AC relay to the left, which perhaps died and somebody rigged up the modern plastic body relay instead.
33222 and 33293 are the Lucas part numbers if you need to order them from one of the parts vendors. We can recommend some if needed. F and D are incremental improvements Lucas made in each. Lucas also tended to supercede old part numbers with new ones so a vendor might have a recommended replacement part number. The last numbers 4264 and 1686 might be production date codes although usually they are just a month and 2-digit year.

Despite being American I know very little about Chevy engines, but it appears you have a coil built in to the distributor cap. So you need to figure out how to connect 12 volts to that coil.
It has a carburetor, and being a Series 1 the original engine was also carbs, so your SU fuel pump in the trunk should work ok to get it to run.
The Lucas starter relay should work ok to power the Chevy starter solenoid.

Its difficult to guess what is going in with that nest of wires on the right hand fender, but it might be the horn relay and the original coil?

Bit by bit, the mystery clears.

I don’t know, but suspect the S1 has two fuel pumps, one in each tank. But, The carb on the SBC would be happy with the fuel delivered by them. Carb’s on the Jaguar engine, carb on the SBC.

The volts will be pleased with most any 30 or 40 amp relay. Easily available and not costly. Bosch or generic, usually just fine.


Ok since I had no idea there was a lump forum I will head that direction. I was hoping to salvage original wiring as much as possible, but maybe I will just have to set up each circuit separate. I was really hoping to find a brown wire to hook up all power then run a relay for the starter and a 12v hot for Ignition and a signal and power wire for Alt.

Jumping over to the lump forum.

Thanks guys. Learning a bit… For example, next time I take on such a project I will look a lot closer at the wiring issues.

It’s a pity the original Jaguar wiring had been left intact, Rob - the wiring, colours showing functions, could be easily transposed to the SBC. Both engines have the same basic requirements - and wiring up from scratch is equally laborious for either forum. The controls, switches etc, relates to the car - and the connections to the engine starts there…

xj6 85 Sov Europe (UK/NZ)

Yes, it appears the original 6RA starter relay is still in place and could be used. The terminals on this should be marked W1 W2 C1 C2 for Windings and Contacts and it works just like any other relay with 30 85 86 87 markings. The original starter motor was on the right rear, so look there for wires that went to it. The original distributor was on the right front and the alternator on the left front. There was also an oil pressure wire on the right and a water temperature wire on the right.

Well the lump section looks pretty dead. I am going to try and figure out the original starting relay and go from there. Any diagram on this unit available? Or anyone have a quick Sketch? I am hoping to try and run a power wire to the key switch in for the larger brown wire, then go onto this relay for starting. Then head from there… Wish me luck, I have a feeling I will b fighting this come summer on my free time…

Let us know the markings on the underside, or a photo, some relays had 4 terminals and some had 5 so there would be a C3. Mine is a type 22RA and has 7 but two pairs are connected so its really 5.

It would be useful to get a clearer picture of what is not working, Rob - but restricting this to the cranking is a good start…
as any…

The later relay should have markings C1/C2/C3 (or, on the S1; only C1 andC2) that are interconnected when the relay is operated (like 30 and 87 on usual relays). Further; W1/W2 which operates the relay when current is flowing through the relay coil connected to W1/W2 (like 85 and 86 on usual relays)…

Starter relay function; C1 (or C2) is connected (originally brown) to battery power. C2 (or C1) is connected (originally white/red) to starter solenoid. W2 is connected (originally white/yellow) to ignition key - powered with key to ‘crank’. W1 is connected (originally black/green) to ground via a start inhibit switch - which prevents cranking unless the gearbox is in ‘P’ or ‘N’. This switch may be on the on the gearbox or linkages - it’s a standard feature with all automatic boxes. For testing purposes the W1 may be connected directly to ground…

As the ign key is turned to ‘crank’, power is applied to the relay W2 and C1 is connected to C2, the starter solenoid operates and the starter is connected to the battery - and engine cranks…:slight_smile:

The starter solenoid draws fairly high current, but any relay rated suitably may be used as a starter relay. Having found the relay; ensure that the wires (whatever the colours on the rewiring done) go to their proper destinations. It’s the wires that carries current, not their colours…:slight_smile:

xj6 85 Sov Europe (UK/NZ)

Here is a 33222 relay.

How it works:

W1 and W2 are two ends of a Winding or coil of wire, i.e. an electromagnet.
C1, C2 and C3 are “make & break” Contact points.
C1 is connected to the small terminal on the starter solenoid.
C2 is connected to positive all the time.
C3 is for something normally connected but you want to be switched off while cranking, like maybe a ballast resistor in the ignition circuit or a AC clutch or both. Your wiring diagram should show what it is.
When the trans is in Park or Neutral, a switch is closed and terminal W2 is connected to ground.
When the ignition key is turned to Start, positive is connected to W1 and the relay coil electromagnet is energized and pulls down a spring loaded contact arm.
C2 contacts C1 while disconnecting from C3, so it should crank with full voltage to the coil.

Awesome. Now I am getting some place. We are cutting the wire harness to make sure where wires end, but for now we have the start solenoid as shown below. It does not appear to have the right colored wires, but it is there and I was able to hear it click with a quick test. going to check continuity.

Here is a closer look at the relay. I have it figured out assuming everything is working. Now to get power from the battery to ignition switch.

So At the key switch I have the brown heavy and the lght brown wires. They only travel a short distance to a plug connector where the wires are all cloth wrapped and appear to have no color marking. Does anyone know or have a picture where these wires would terminate at the battery power source? If not could I run a fused power wire directly from the battery to the 2 brown wires at the switch?

Thanks a bunch. If needed I can easily post pics of my switch.