[xk] XK-150 4 Way Emergency Flash

It appears that it would be reasonably easy to add circuitry to the
XK-150 turn signal system that incorporates the Lucas DB 10
Stop/Flasher Relay to allow Emergency Flashing of all 4 turn signal
bulbs. The circuit would bypass the steering column mounted turn
signal switch with connections from both sides of the Lucas Relay
(terminals 4 and 8) to a switched or unswitched power supply.
Unswitched power to the Lucas DB 10 and also to the flasher would,
of course, be required for emergency flashing with the ignition
switch off.

Such connections will activate both the right and left flashing
relays in the DB 10 for simultaneous flashing on all four corners,
as has been confirmed with jumpers. It should be noted that LED
stop/tail lights have been installed and a heavy duty flasher good
for 1 to 4 bulbs has been installed. With the LED�s, the flasher
probably sees the equivalent of about 2 1/2 normal bulbs for 4 way
flashing. Also, the electrical system is still positive ground.

The wiring and 3PDT switch necessary to make the connections to a
fused, unswitched power supply (cigar lighter terminal) can all go
behind the dash. The wire to the flasher and the DB 10 should not
be too terribly overtaxed since the current is only about 1 amp
higher than the current for flashing 2 normal bulbs.

Before doing this installation, I would be interested in knowing if
anyone else has done something similar, and if so, how has the DB
10 endured the additional load for extended periods. Also, the
power supply for the flasher connects to the fuel gauge with a
common ring terminal connection shared with another green wire.
(Actually, two rings with paired wires are connected to the
terminal.) Does anyone know what the other shared green wire goes
to so acceptability of switching it to a temporary unswitched
source can be determined?

As a side note, a Radio Shack chime was installed to indicate when
the turn signals were on, since the left signal often fails to
cancel. The constant �ding dong� was unbearably obnoxious, so an
adjustable time delay (2 to 60 second) relay was placed in the
circuit. The modification is still being tested and adjusted, but
it looks like it might be a helpful solution for my
inadvertent �flashing�. The chime would also be an indicator that
the emergency flasher is in operation, obnoxious as it is.–
Don Snyder, '59 XK-150 DHC, '73 E-Type 2+2
San Antonio, Tx., United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

In reply to a message from Don Snyder sent Tue 18 Jun 2013:

Don if you take a look in the electrical section of Jaguar workshop
manuals from 66-67 you will find a schematic of the Lucas add on
flasher as they became mandatory. An extended harness should be all
you need and the power supply need not come from that green. All of
my ‘‘older’’ Jags have the 4 way as it was a period add on and
approved for retro fit. No Idea about your led lamps and the load.–
The original message included these comments:

It appears that it would be reasonably easy to add circuitry to the
XK-150 turn signal system that incorporates the Lucas DB 10
Stop/Flasher Relay to allow Emergency Flashing of all 4 turn signal

George Camp
Columbia SC, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

Resurrecting this thread, I’ve just tried to connect a period-ish flasher to my 150:

However, after integrating it with the car’s original DB10 relay, the lights blink normally for the first two times, then begin to “flutter.” You can hear the relay fluttering as well.

Are these newer units just incompatible with the old DB10s?


As I understand it, the DB10 relay is to connect either the left hand lamps or the right hand lamps to the flasher unit. Thus, your hazard circuit would not activate the relay, just connect its outputs to the four lamp connections on the relay.

Is it your hazard lights that flutter, or you regular indicators?

Common reasons for indicators to flash erratically are bad earth/ground connections at the lamp holders as rate of flashing is determined by lamp resistance.



Thanks for your reply, it gave me the insight needed to solve the puzzle. Here’s what I found to work on my early roadster:

If you connect the Hazard Unit according to Lucas’ instructions, the GR and GW output wires connect to the turn signal switch, which runs directly to the inputs to the DB10 relay (terminals 4 and 8). As I described in my post above, that causes some sort of mayhem inside the DB10.

However, connecting the GR and GW wires to the OUTPUT of the DB10 as you suggested (and shown above), it works normally.

A couple additional notes;

  1. the Hazard Switch leads (G and GB) must be installed between the fuse box and the regular turn signal flasher unit. This is because turning on the hazard unit disables the turn signal flasher so they can’t both be run at the same time.

  2. On my MKII, the Hazard Unit was virtually plug and play. But on the older XK circuit, I had to fabricate several pigtails for it; one between the Hazard Unit and the DB10 relay, one between the Hazard Unit and the turn signal flasher, a power lead from the non-fused side of the fuse box to the Hazard Unit (the unit has its own fuse), and a ground wire.

  3. The Lucas Hazard Unit can be adjusted for use on POS ground cars. The provided instructions include a good diagram, although I’ve only shown the ones that run external to the unit.

  4. Other than adding the Hazard switch between the fuse box and flasher, all other original wiring on the XK can remain in place and unmodified.