Jaguar XJ6 V8: Christmas 2015

Dateline - 12/24 and 12/26 2015 - I had two solid days on the car over Christmas break and got a lot done, although it really doesn't look like it from pictures.

Thursday 12/24/2015:
First thing I wanted to do was re-route the fuel line to the carb. I didn't like it being so close the the heater hoses, so I moved it around to the other side. Next I put the hose clamps on the heater hoses. I purchased hose clamps that have chrome anodized aluminum fitting that make them look like pressure fittings. It's a bit of bling that looks so much better then plain old hose clamps. I also put on the new distributor cap, which required removing the HEI coil and plug wires from the old one and installing them into the new. Simple swap but I like the looks much more than the black cap that was on there.

That was all the easy stuff! Next I decided to tackle the wiring. I've been holding off on this because I knew it was going to be a bear and I wasn't disappointed! All the original wiring was left in the car after the engine swap out. A wiring harness that came with the engine swap kit interfaces between the old and the new. I wanted to get rid of the old wiring that wasn't needed, so I had to figure out how it worked as installed. It took me several hours of tracing wire, looking at schematics and puzzling over what I had in front of me to figure it all out.

The first puzzle was the starter relay. This had all the original connections, but some had been removed by someone (me) who did not mark the wires (DUMB!) so I wasn't sure how things needed to go back together. I had to split apart the wiring harnesses and pull apart connections in the car to trace where all the wires went. The key was finding the wire that goes from the ignition switch START to the relay. Because of my extensive re-wire and the the wire color code changing between the engine bay and the inside of the car (Jaguar!) this was no easy feat. I ended up spending about 1.5 hours with an ohm meeting probing at wires until I figured it out.

Next I had the find the Starter Isolation switch wire which breaks the ground side of the starter relay. This switch is mounted on the gear shift and is only activated when the car is in Park or Neutral. This way you can't start the car while in gear. 20 minutes with an ohm meter and I found the wire. So, now I had everything I needed to hook up the relay.

But of course, I couldn't put a nasty old corroded relay back into the car. So I spend some time with some metal polish and shined it up to a nice bright gloss! Then I mounted the relay next to the battery cutout relay, plugged in the wires and voila!

My next challenge was the wiring harness going to the engine. This thing was nightmare. This is a harness that come with the engine swap kit so it has a plug that plugs into the existing wiring harness, which is good, but it also has a bunch of extra wires for different Jaguar installations and I had to figure out which were originally used. I basically needed three wires: 1) A hot wire going from the ignition to the distributor "BAT" terminal, 2) A wire for the oil pressure sender and 3) a hot wire to the automatic choke on there carb. Once I figured out those wires, I was able remove the unneeded wires, which reduced the complexity quite a bit.

From the alternator, I have the hot wire that goes to the battery, which doesn't use the existing wiring in the car. Instead a large lead runs from the alternator, across the top of the engine and out the back to the right side hot connection terminal on the firewall.

The alternator also has a plug that has two wires. One is a hot that energizes the alternator the other is a wire that goes to the "ignition warning light" on the dash. The hot was easy (just used what was there before) but the ignition warning lamp had me scratching my head because I could not see this ever being hooked up. It had a bullet connector and there was no wiring in the car where this would fit. So I'm thinking it was never hooked up. So I covered the bullet connector and buried the wire back into the harness. I figured if I need it, it will be there and I can easily pull it back out.

While working on this harness, I had a nagging question running in the back of my mind. "What about the tachometer?" My experience with cars has been that the tach usually uses a wire that connects to the coil to sense how often the coil is firing. Well, the HEI unit has a "TACH" plug, but the existing wiring harness has no wire connected to that. This meant that the tach was getting a signal from someplace else.

Now the real head scratching began. How did the tach work? I had to figure this out because I have an aftermarket tack to put in and need to make sure it gets wired in correctly. When I look at the wires and trace things down, I have a wire running from the tach to one side of the ballast resistor. On the other side of the resistor I have two wires ganged together, one that runs to the HEI unit and other that goes to the starter relay which I had disconnected as not needed (see above). How did all of this work? Finally it occurs to me. Instead of running a hot from the ignition to the ballast relay, to the coil, and another wire from the coil to the tach, Jaguar ran the hot from the ignition through the tack, through the ballast relay, to the coil. This reduced the amount of wire needed. Of course, if you ever remove the tach, the engine wouldn't run, but who would ever do that?

But what about the hot lead coming from the starter relay going to the coil side of the ballast resistor? To answer that, we need to review the principles of coil based ignition systems (believe me, I had to look all this up!). The average coil only needs about 9 volts to operate effectively. If you run a coil at a constant 12 volts, you will overheat the coil and cause premature failure. So, to get the maximum life from the coil, you need to step down the voltage. The easy way to do this is a resister placed in series. Thus, the ballast resister was born.

But why put 9 volt coils in to begin with? Why not make then 12 volts? Hearken back to the days of yor when cars had very low tech carburetors, suspect fuel quality and low compression engines. Remember, you need three things to get an engine to run, fuel, compression and spark. In the above scenario, two of the three things you need are poor (fuel and compression). So what can you do to help the engine start? Have a very hot spark. And how would you do that? Over-energize the coil! So, in many cars, there is a bypass wire that goes from the starter relay to the coil that will put 12 volts to the coil when the engine is being started to get a hotter spark. As soon as the car starts, the coil voltage dropped back to 9 volts and everyone is happy. Pretty ingenious actually! Now this is all fine and good when you have a coil. HEI systems don't need the power reduction so I could get rid of the ballast resister. That left me with a spare wire running from the starter relay to the now missing ballast resister. I'll get back to this wire in a moment.

But I still have a problem. My tach needs a separate power and tach signal to work. So, I took the original wire that went from the tack to the HEI unit, cut it and connected it to an unused wire in the new wiring harness and plugged that into the TACH pin of the HEI unit. I then spliced the HEI BAT wire into the now unused wire that went starter relay/ballast resister which will go to ignition hot (yet to be determined). So, this should give me hot when the ignition is on, a tach signal and removed the ballast resister. What a pain, but boy did I feel good once I got this figured out!

My next challenge was mounting the horn relay. Not too bad. Of course, I had to polish it too so that it had the right look!

That was enough for one day!

Saturday, 12/26/2015:
More wiring! I decided to focus on the bunch of wires I have on the left had side of the car. Here I have:

Transmission torque converter lock relay signal
Speedometer sensor power and signal
Cruse control magnet pickup wires
Oil pressure sender
Water temperature sender

Everything but the water temperature sender needs to be bundled and run across the top of the firewall, then down into the transmission tunnel. The oil pressure sender wire comes out of the bundle part way down to run across the gap between the firewall and engine. This was all pretty straight forward. I may not need the Cruse control magnet pickup wires if I can successfully get the signal from the tachometer. I still ran the wires, just in case. If I don't need them, I'll strap everything up under the car.

I also had a wire to run to the water temperature sender which needed to be wrapped up with the wires going to the cruse control. I had already wrapped those wires, so I needed to unwrap and re-wrap them. I hate doing things twice (or three or four times) but it needs to be right.

I next spent some time installing the cruse control linkage. Since I already have a lot of linkage for the throttle and transmission kick-down, it was a pretty easy go to drill a hole in the brackets and install the cruse control linkage. The kit came with a lot of options and I was able to use the easiest method. Nice to have something easy for a change!

My next challenge was the radiator and electric fan. As with most aftermarket items, the fan did not quite fit the radiator (a little small), so I had to spend a couple of hours "engineering" a solution. The kit came with brackets that I was able to use with plenty of spacers, but unfortunately the bolts I have are not long enough. So, I need to make a run to the hardware store for some more!

I also needed to wire up the fan. There three ways to do this. I can wire it to be full speed all the time, slow speed part time and full speed when needed, or off until a temperature is reached, then slow speed until it reaches a higher temperature then full speed. The last two require a thermostat that I don't have. I like the idea and will probably get the thermostat, but right now I wired it to be full speed all the time.

I also need to find a 20 amp hot to power the fan, and a hot from ignition to run the fan relay. I didn't get that far though. I did get the relay polished up and mounted. After that, I was done for the day.

BTW - You may be asking what about the voltage regulator? It's still hanging out there (literally). I've not decided if I want to leave it in or not. I'm thinking yes, but I'm still undecided.

Here are some pictures.