Running Wires Through Firewall

I’m getting ready to hook up my new water temp and oil pressure gauges (where the trip computer used to be), and am wondering if anybody has found the perfect place to run wires through the firewall? I’ve got the throttle plate open right now, wondering if that would work. Or drill a hole somewhere in the firewall and install a grommet?
Thanks!

Greg,
A couple of years ago I modified my wife’s 1990 XJ-S convertible to run a new wire from the auxiliary cooling fan to the interior of her car to illuminate the green “Caravan” light on the dashboard whenever the auxiliary cooling fan is on. I did this after we had some instances when the cooling fan did not come on when it should have. At least one time it was due to a failed relay, but I wasn’t certain of what caused the other times. It is nice to see that green advisory light come on and go off from time to time confirming that the cooling fan is working properly.

If you search the Jag-Lovers archives for “caravan light” you will find my post from Sept 2017 that includes pictures of how I routed this new wire to the dashboard by using existing wiring routes. I did not cut any holes in the car to do this. This was relatively easy to do and I am quite pleased with the wire route I used.

Paul

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Thank Paul, found it. And that’s such a cool (no pun intended) idea! I may also run a wire to my caravan light to know when the aux fan is on.

BTW, this is where my vertical gauge sits when car is totally warmed up at around 200F. This is based on my accurate readings with a temperature sender right behind thermostat on B bank.

Is this accurate? Or is my vertical gauge off?

image

Greg,
That coolant temperature reading appears a bit low from my experience, but of course cars, thermostats, wiring, gauges, and climate can all affect this.
Attached are two pictures that I took while driving my wife’s 1990 XJ-S convertible after I made the “Caravan Light Modification”. The first picture shows what I would consider a normal coolant temperature reading while driving the car, at the center of the N and the auxiliary cooling fan off. The second picture shows an elevated coolant temperature reading, probably after climbing one of the hills on the way to our house, and with the green “Caravan” light illuminated showing that the auxiliary cooling fan is powered on and the temperature at the top of the N.
These pictures show the normal coolant temperature readings in my wife’s car (1990 5.3L V12 w/ Marelli ignition)

, but of course your readings could be different and still be perfectly fine.
It is interesting to observe the “Caravan” advisory light coming on and going off during normal driving. It is a nice reassurance that things are working properly on a few important parts of the cooling system.


Paul

i guess a comparison to actual coolant temperature is needed, but thanks for that. I’ll monitor mine in the future along with my aftermarket temp gauge.

My oil pressure at warm idle is also a bit below the 50. Yet my aftermarket oil gauge read 50psi.

If I have to take the instrument panel out again, I may do another cleaning. I’ve grounded it, so it should be getting a good 12V.

I once heard (anecdotal) that the early V12 owners were complaining of the temp gauge reading high, the remedy for the workshop was to take the guage out and ‘reposition’ the needle. Believe what you will :slight_smile:

Mine…Below center : cool days around town …slightly above: warm days on the road. These guages seem to be relative. Not all the same…ambient temps and driving habits variable. Too many guages equals too much excessive worrying. Check temps with an infra red temp gun…I have one that I use more in the kitchen for cooking than on the car .

After a long ride my oil p. goes next to 0…I believe that is de riguere.

I also tested with an infrared gun at one point. Outside of thermostat was 197F, but temp gauge was reading 205F. So a bit hotter inside.

This is why I will like having dual temp senders with actual degrees. I’ve re-purposed the box for the trip meter and bolted a new faceplate onto it with three holes cut out for my gauges (could only fit 1 1/2" electric gauges, Equus makes some). So it all fits snugly into slot, and I simply use a screwdriver to pry it out, like the trip meter. I can post photos later if anybody is interested. Very easy to wire up with existing positive/ground wires. Only issue is getting wires from senders to here, but Paul has helped me discover where to go.

I remember reading it somewhere, but can’t find it. Why do V12s, when they first start up, read low oil pressure and low charging voltage? But as soon as you rev it a bit and the engine starts warming up, you get good readings? My oil pressure goes from 20psi to 50psi, and my charging voltage goes from 12V to 15V at idle.

BECAUSE IT IS A JAGUAR…one has to accept with blind faith that this car will operate contrary to all known logic, this comment is directed especially to a non-British owner.

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Actually, the oil pressure tends to read high at startup and then drop to alarminglylevels low after warm up. If the AAV is not properly adjusted (high enough), a warm engine at a stoplight will turn the low pressure light on. The Voltages at idle do tend to be higher, but of no concern.

That’s weird, mine seems to be the opposite. When warmed up, I was getting a good 50 psi at idle in P (850rpm), and about 60psi revving it up a bit.
I’ll double check once I get my gauge set up.

My oil sequence is…start engine…guage shows 0…very slowly creeps up to about 50-55…as engine warms up, at idle the pressure drops …the warmer the engine the more it drops…rev-up and pressure goes up…probably because of how the sensor works and where it is located on the engine. …this seems to be a common worry…most of us are used to something else

I remember a thread couple of years back which talked of Oil Pressure, and the Jaguar revision of the oil pressure transducer to always send a middle of the gauge reading.
I tried one of them and it lasted about 2 days before I put the old one back in- – I would rather see the gauge showing different levels of pressure.

At start-up i turn the key, wait for check engine light to disappear, then crank. During crank I focus on the red idiot light. Usually takes about 4-5 seconds to go out and about the same time that light goes out the pressure needle can be seen rapidly moving up to about 55-60 psi and then comes down to about 50-55 psi over the warm-up.

When driving my oil pressure needle fluctuates with RPM levels, as expected. At stoplight with fully warm engine it drops down to essentially unreadable. The I monitor the idiot light - - as long as red light was working earlier and went out at start, I expect it still to be working during this drive. As long as light stays off I assume I am at least 5 psi. When light turns green and we pull away, pressure comes up again. Sometimes the Jaguar Paranoia creeps in and I will slightly rev the engine at stop light just to see the pressure needle move…kinda like watching my dog sometimes to see if she is breathing :slight_smile:

This is why I’ve installed an aftermarket oil gauge. For all you know, you’ve got a voltage issue going to your instrument panel, or that vertical gauge is a bit ‘dirty’. I just don’t trust them, after seeing all the corrosion on mine, and seeing how so much depends on that flakey circuit board.