The 'E' Type Forum

A neighbour of mine has a 1966 Series 1 4.2 Coupe (originally LHD) with the clock in the tachometer.

The clock is currently not fitted and he wants to put it in after testing but is confused as to where the +ive and - ive side of the clock is.

The handbook says that after chassis 888543 (LHD) to connect the -ive wire to the +ive tab and the +ive wire to the -ive side of the clock - so basically even though the car is -ive earth the clock is to be connected as if it was +ive earth. To further confuse matters his Car is 1E32873, Body 4E24228 so not sure if this applies.


However - despite the advice in the workshop manual the markings on the back of the clock show that +ive should be connected to positive and -ive should be connected to negative as per other -ive earth cars like my Series 3 which is a much better design than the old 6 cylinder bangers


Any advice to solve this confusion would be appreciated.

Thanks

Garry

My only confusion is why you refer to a 3.8 workshop manual for a positive earth car as guidance for a negative earth 4.2 car. You'll find very many other major things in the 3.8 electrical manual that don't chime with your friend's car if you do that.

Looking at the correct wiring diagram, however, in the 4.2 section, everything is clear and you should follow the clock markings (which unsurprisingly match the car's actual electrical system).

The only reason for the specific paragraph you photographed is I presume because earlier purely electro-mechanical versions of the clock could survive accidental reversed polarity connection. Once the delicate semiconductor was added (I'd guess a germanium diode to prevent backflow), it would be toast as soon as you hooked it up wrongly.

In general, given the age of our cars and the possibility of prior work or parts substitution, where there is ambiguity I would always go by what you had in your hand, rather than follow the original spec which might no longer apply 50+ years later.

PeterCrespin wrote:My only confusion is why you refer to a 3.8 workshop manual for a positive earth car as guidance for a negative earth 4.2 car.

Well I thought the same and the pic of the instructions is out of the owners workshop manual.

So before posting I checked my own Scientific 4.2 manual and the statement is exactly the same.



Hence my and the owners confusion.

As far as the wiring diagrams go - also checked them - as far as the clock goes checked them as well - both a positive and a negative supply and no other information - the 3.8 has the clock as a rectangular box and the 4.2 as a circle as the clock - otherwise the wiring of the clock in the diagrams is the same.

So I take it from your comments that that the clock is to be connected as it should be - positive to the clock and negative to the earth.

Thanks

garry

garrycol wrote: So before posting I checked my own Scientific 4.2 manual and the statement is exactly the same. Hence my and the owners confusion.

As far as the wiring diagrams go - also checked them - as far as the clock goes checked them as well - both a positive and a negative supply and no other information - the 3.8 has the clock as a rectangular box and the 4.2 as a circle as the clock - otherwise the wiring of the clock in the diagrams is the same.

So I take it from your comments that that the clock is to be connected as it should be - positive to the clock and negative to the earth.

Still some mix up I fear.

1) The main manual was written for the original 3.8 version of the car, which was positive earth (negative clock feed) and used serial numbers without prefix, in the 85xxxx to 88xxxx range as shown in your photo from the 3.8 section of the manual.

When the 4.2 came out there was supplement and again for Series 2 etc. These are today bound into the same book but constitute different manuals. So you obviously need to look in the 4.2 part for 4.2 info. There's no such thing as a 4.2 (all negative earth) with a 3.8 VIN of the sort shown in your photo, hence the positive earth clock info in the photo is in the 3.8 section, applies only to 3.8 cars using those VINs and cannot apply to 4.2 cars.

Nor does the positive earth wiring diagram shown in the 3.8 section - which is the only one showing positive earth clock feed - apply to a 4.2.

If you use the wiring info in the 4.2 section it is referenced for the correct 4.2 type VIN 1Exxxxx (no confusion) and is also negative earth (no confusion) and therefore matches your friends dash clock markings (no confusion). Ergo, any confusion is because you're looking in the wrong place and using 3.8 info on a 4.2 car.

Thanks - your comments may be relevant to an original Jaguar workshop manual but not the Scientific Manual I have - other than the wiring diagram there is no specific 4.2 section and the Contents and index covers 3.8 and 4.2 together - I suspect the issue is with the manual itself - there is no supplement.

Irrespective of that, you have answered my question and I am thankful for that - I have passed the information onto the owner and tomorrow we will see if the clock actually works.

I assume it is the same as my Series 3 clock in that the clock is mechanical and is just wound up electrically.

Cheers

Garry

I only know of the original Jag manuals and the Bentley big green compilation softback, plus the Haynes. These are all based on the same original artwork and text although the Haynes does have different content.

In any case, your photo, which is a copy of the original typesetting from Jag, is self-validating no matter where the editors of your version place it in the book. It lists 3.8 serial numbers to which the info applies and does not show 4.2 numbers so it doesn't apply to them. The wiring diagrams are the other way around IIRC. The 3.8 positive earth ones are just the originals and therefore show a dynamo, separate solenoid etc. but no serial numbers, whereas the 4.2 ones are negative earth alternator versions and list the 4.2 vin numbers like your friend's car. So again those diagrams are self-validating where ever they appear in your Oz version of the manual, assuming the editors didn't maliciously strip out the 4.2 vins or other key info.

Actually I tell a lie. Somewhere I do have an American hardback thing (Clymer?) which is a slim item with a vaguely pretty washed-out picture on the front but comparatively lightweight and useless, with lots of knowledge gaps. I think of it as the Miley Cyrus of E-type manuals, because it doesn't cover much.

garrycol wrote:
The clock is currently not fitted and he wants to put it in after testing but is confused as to where the +ive and - ive side of the clock is.

In my experience it doesn't matter as the damn things never work anyway.

abowie wrote:In my experience it doesn't matter as the damn things never work anyway.

Just like to say that mine is fully adjusted and keeps perfect time...

< Engages smug self-satisfied smile of the Series II owner >