Tech Tips

Under-Dash Electrical Fire
Instrument Panel Lighting Switch/Rheostat
All Triumph Models 

To avoid the potential for overheating of the instru-
ment panel switch/rheostat and possibility of an
under-dash electrical/insulation fire, DO NOT
change the bulb wattage specified by the factory and
DO NOT wire any additional lamps or devices into
the instrument illumination circuit. 

With Triumph/Lucas wiring systems, the electrical
feed for this instrument lamp circuit is from the
fused side of the rear light wiring and is a solid red
colour to the panel light switch/rheostat, (this is a
ceramic mounted, open wound, variable resistor).
The wiring from the switch to the instrument lamps
will be red with a white tracer. No additional lamps
should be wired into this red/white wire or circuit!
It should feed only the instrument lamps as in-
stalled by the factory. 

Fusing of the rear light circuit with greater amper-
age than specified, may result in severe overheating
of the instrument light switch IF an electrical short
occurs between the switch and the lamp(s) with the
switch in partial-to-full-dim positions. (Note: it is
debatable as to whether the existing specified rear
lamp fuse would recognize a short circuit with the
switch in partial or full-dim position). Therefore, in-
stallation of an accessible low amperage (3A) "in-
line" fuse on the red or red/white tracer connection
at the switch during dash re-wiring or harness/
loom replacement, is recommended. 

As the instrument panel lights are fed from the
"fused" side of the rear lamp circuit, the lack of
dash lights may indicate that the vehicle’s rear park/
running lights are inoperative. This is a design fea-
ture to alert the driver that the rear lights are not op-
erating due to a "blown" fuse. 

When night driving, having the instrument light
switch at maximum brilliance will produce the least
heat from the rheostat and prevent heat degradation
of the switch and electrical insulation that may be in
close proximity to the switch. Conversely, having
the instrument lights dimmed to minimum light lev-
el will generate the greatest amount of heat. 

Total Brake Failure 

Loss Of Fluid/Brake Line Abrasion
Triumph TR4/TR4A Models 

Owners of the above models should check that
the chassis-to-engine electrical grounding
strap, adjacent to the left engine mount, is not
in contact with the steel brake line feeding the
left front wheel. 

Due to movement of this strap from engine vi-
bration, the steel brake line can abrade and
wear to the point of rupture under hard brak-
ing or result in brake fluid loss. In both cases,
total brake system failure can result. 

Ignition Timing Marks (Dynamic Timing)
Timing Pulley/Graduation Marking 

All Models 

A quick and easy method to improve visibility
of graduated scale and crankshaft pulley tim-
ing marks is to use ordinary office stationery
"white out". The bottle comes with a very con-
venient brush and the application of a small
"dot" on the crank pulley and the static scale, at
the correct graduation mark, will enhance visi-
bility when using a timing/strobe light. 

Illuminated Plastic Knob Repair
Hazard Flasher Pull-Type Switch
Triumph TR6/ Spitfire 

Triumph vehicles fitted with the Lucas "pull-
type" hazard flasher switch can suffer stress
fracture (cracking) of the illuminated red plastic
knob resulting in inoperable safety feature. (The
knob pulls off!). This fracturing is a result of
both enbrittlement and tightness of the switch.
If merely cracked, a satisfactory repair can be
made by applying a 1/2" section of 1/2" heat
shrink tubing directly over the threaded section
with a heat shrink gun. To prevent deforming
of the knob while heat shrinking, screw in a 3/
8" NF bolt to support the shank area. Do not
apply too much heat, only enough to effect a
good looking and tight repair. As these knobs
are no longer available, this repair can be done
to strengthen a knob that is still intact.