[pre-xk] Mark V turn signal wiring

My despatch date is 18 April 1950. The car was sold by Hoffman in New York.

I could explain the turn signal wiring better. The car has what I take to be
the normal cloth wrapped harness, including wiring for trafficators that in
the saloon run over the headliner struts, and which in my car are wrapped
back and tucked in the roof rather than dangling down to there they would be
plugged into trafficators if I had them. The wiring to the front and rear
sidelights and brake lights are wrapped in with the cloth wrapped harness,
but the turn signal wires in front and back are separate single wires, not
wrapped with the others. So they took a harness for a trafficator car and
just added some extra loose wires for turn signals.

I don’t understand why there would be a RHD wiring diagram for USA turn
signal cars at all. I never see RHD Mark Vs here, I didn’t think they were
ever sold here, and I always thought having LHD was a major selling point
Lyons wanted for breaking into this market. I studied it for awhile before I
figured out that the only difference from the LHD USA diagram is the
location of the large terminal block on the inner valence of the front wing,
which will be on whichever side the steering column is.

The only difference between my saloon and your DHC should be that I have two
interior lights in the rear corners where you have one in the center of the
hood. I think you can use W76522 and just ignore the second light. My main
harness runs through the right hand sill and the interior light wiring
branches off at the right rear corner above the inner fender so that should
be pretty much the same as yours.

I agree that the Mark V turn signal system is much better than the double
relay brake light interrupter they used on all the other models through the
Rob Reilly - 627933> When was your MKV made Rob?

My MKV DHC ch. 647194 date of manufacture July 14th 1950 has
original flashers, no trafficators and the wiring is as per
the factory Service manual, except that for some strange
reason for the DHC the wiring is exactly like in the ‘‘RHD
for USA’’ schematic, which I think has got to be a typo
because AFAIK they only made these for the North American
market, in Europe and commonwealth countries they used
trafficators for a lot longer, also with MKVII’s.

Lucas Wiring Diagram No. W76422, which is for the Saloon (1949)

and the same for No. W76522 which says (LHD for USA) 1949
also Saloon, I guess they didn’t bother to do a new
schematic at all for the DHC, but it seems it is the same
except for the small differences of the interior light (No.
W76520 Coupe Mark V 1949 (LHD Export Models)) and the fact
that the routing of soem cables was a bit different due to
the different body and sills.

My hacked and in poor shape wiring harness does carry the
wires for the flasher, I will be replacing the complete
harness when the body comes of for repairs and a bare metal
respray, but I think that won’t be within a couple of years.

I think it was a pretty neat solution with a separate relay
and double filament bulbs in the front side lights and
double bulbs in the rear lights, in comparison to some of
the MKVII relay and combined stop light and flasher hassle.

Pekka T. - 647194

The original message included these comments:

My USA version Mark V has extra wire extensions for the flashing turn
signals, not part of the main wiring harness. Most Mark Vs had
but this is the way the factory did it for cars with turn signals.
Rob Reilly - 627933

In reply to a message from R_and_J_Reilly sent Wed 8 Sep 2010:

Can anyone help with a small dilemma on my car wiring? The car is
628166 LHD 3 1/2 Mark V delivered to Los Angeles summer 1950. It
has always had turn signals, not trafficators. The car has turn
signal/horn wiring that don’t seem to match service manual diagrams
in my possession. My spare car has a substantially different
electrical system in this department and so it is not much help.

The car in question has a three-tab flasher unit (labels X, P, L)
similar to the Lucas Technical Service Overseas Correspondence
Course Section 8, p.50, just saying X,P,L rather than B,P,L (for
battery, dash pilot light, and signal lights). Next to the thermal
flasher unit on the left hand sidewall of the engine compartment is
a Lucas DB10 relay box (see p.51 of same manual). The relay box and
the flasher function correctly. I have used the signals, horn, and
exterior lights for years with fine electrical functioning.

On rebuilding the engine, I took the time to replace the inner
elements on the steering column without paying much attention to
the previous wiring. When assembling everything back, I have
discovered there is no 12 volt supply to the center feed for the
signals or for the flasher unit. My guess is that this was provided
via some connection in the steering between the horn feed and the
center feed, but this is not clear to me. It seems to me the power
should be fed to the ‘‘X’’ point on the flasher unit, with the ‘‘X’’
point also supplying the steering column center feed. A line from
the battery to do that makes everything work fine.

The circuit diagrams I have don’t seem to show the relay box. Does
someone have a circuit diagram with the relay box shown, or can you
guide me as to how I am misreading the service manual diagrams?

Where is the 12 volt supply line for the flasher to power the turn
signals and simultaneously powering steering column center feed to
throw the relays, or shall I just find one post ignition switch?–
Roger McWilliams
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In reply to a message from Roger McWilliams sent Tue 14 Sep 2010:


There should be a Green (ignition) wire to both the flasher unit X
or B terminal AND to the centre of the indicator switch. If you can
visualise the DB10 box as two separate relays it make more sense.
When you turn (say left) it selects that relay which disconnects
the left stop lamp and connects the flasher unit to the left front
signal and the left stop lamp. The flasher unit is a series wired
load sensitive unit is connected and flashes. The P terminal on the
flasher is to the warning lamp

The DB10 connection are as follows:-

Terminal 1 = Green/Brown from L terminal of flasher unit
Terminal 2 = Green/Red to LH front lamp
Terminal 3 = White/Purple to LH Stop lamp
Terminal 4 = Green/Blue from LH indicator swich
Terminal 5 = Green/Purple from stop lamp switch
Terminal 6 = Green/White to RH front lamp
Terminal 7 = White/Brown to RH Stop lamp
Terminal 8 = Green/Yellow From RH indicator switch

These are the standard colours that were used on MK 7 & 8 plus the
XKs. I can scan the diagram for one of these if you want, just mail
me direct.

The original message included these comments:

The circuit diagrams I have don’t seem to show the relay box. Does
someone have a circuit diagram with the relay box shown, or can you

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The DB10 double relay was used on models which have single bulb taillights
like the Mark VII and XK120. It does not belong on a Mark V, unless they did
something different between my New York delivery 627933 and your 628166
which is probably about 3 weeks newer. Extremely doubtful. Yours should be
the same as mine with two bulbs in the taillight.
You should be using the W76522 diagram same as me. Do you have that one?
There should be 4 wires in the steering column, same as all Mark Vs. On mine
the colors did not match the wiring diagram.
One goes to the horn relay. This is the only one that grounds itself in the
manette control to operate the horn relay.
One goes to an inline connector and on to the flasher terminal L.
The other 2 should go to the large terminal block on the LF inner fender
(wing), where they branch off to the four corner lights. Either of these
should connect to the one for L when you flip the switch either way.
Flasher terminal X has a green wire connecting to the large terminal block,
where another green wire connects to the power terminal A4 on the regulator.
Flasher terminal P has a green & black or green & brown wire connecting to
the large terminal block, where another green & brown wire connects to the
warning light on the dash.
X sends power through to L, which operates either pair of the four flashing
lights, P only operates the dash light, alternating off/on when the outside
flashers go on/off.
Rob Reilly - 627933

In reply to a message from R_and_J_Reilly sent Tue 14 Sep 2010:

Thanks guys for the combined details. Yes, indeed I have the W76522
drawing with Feb 1950 date on it, along with the earlier ones in
printed shop manuals. I also don’t seem to find a later drawing in
the CD version.

My driver car has the flasher unit and this nonexistent relay very
neatly placed on the sidewall midship between the LF terminal block
and the brake wiring output position. There are no wires coming
directly out of any loom wrap, just out of the block and from the
brake switch.

Maybe the factory put it in, as they began switching over for other
models. Maybe the guy who owned it before me had it done. He had
changed the rear lamps out to fender-mounted, hip high, Lucas lamps
as used by Jag and MG later when the California Highway Patrol
asked him to put the lamps higher. I put the rear light assembly
back to original as delivered in California and have had no police
issues over the years.

Given the low rear light location, I think there is some visual
perception advantage to having the signal blink with the associated
brake lamp bulb off during blinking (all these lights shine red, no
yellow for turn signal as for modern cars in California). And since
all the parts work, I’ll just run a post-ignition line close to the
style of W76522.–
Roger McWilliams
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My flasher was also on the left inner fender.
My diagram is the same date.
The DB10 relay should have a date on the cover which might give you a clue
as to when it was installed.
I have had people tell me my brake lights are hard to see when the sun is
behind me. I guess it must be the glass lenses reflect the sun too much.
Could be worse, MGTCs have their little lights below the spare tire, and
last Sunday at the Chicago British Car Festival I noticed a couple of MGTCs
where the owners had added big plastic trailer lights from K-Mart.
Rob Reilly - 627933

In reply to a message from R_and_J_Reilly sent Sat 18 Sep 2010:

Good idea to check the DB10 date code. After scraping off the dirt,
a line which says 12V1166 was found, perhaps this means November
1966? Of course, it might have been a unit replaced in 1966, but it
also leaves open the idea that the DB10 was added later. I wonder
when Jaguar got the DB10 unit in earliest use for any of their
cars. The Mark VII parts manual shows it (C.4518) in use for the
Mark VII. The wiring diagrams for the Mark VII show it in use in
1951 on W79601-1 and W79621-1 and the XK120 diagram W94602. The
build date on this Mark V with the DB10 was 26 June 1950 with a
dispatch date of 2 August 1950 to California.

Got the whole setup running by adding a line from the hot side of
the brake switch to the flasher unit. That seemed reasonably
compatible with the original wiring diagram and keeping current
loads safe on the wires.–
Roger McWilliams
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Yes, it was made in 11/66. Most Lucas parts have a date somewhere on them.
Rob Reilly - 627933> a line which says 12V1166 was found, perhaps this means November


Got a funny surprise today. I cleaned the original pigtail harnesses for my Mark V front turn signal side lights. They are about 2 ft long and run from the sidelights to the connector blocks in the inner wing upper valences.
The left hand signal wire is supposed to be green/red, but it is green/white like the right hand signal wire.

Hmm, I thought left hand electricity wouldn’t go through a right hand wire. It would go the wrong direction, wouldn’t it?

Ok seriously…
Somebody on the factory assembly line grabbed the wrong pigtail and put it in. Maybe they didn’t notice, or figured nobody else would ever notice. Or maybe didn’t have one for the left side. Only one is listed in the SPC, C4565 Lucas 860124 qty 2. Maybe they didn’t care as long as the guy plugged it into the right socket in the block.

Didn’t figure that 71 years later somebody would notice. :thinking:

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