Widget Of The Week
Smiths SR/D366 Automotive
Instrument Tester, 1965?
These days when something goes wrong with your car’s
engine or electrics one of the first tools most mechanics reach for is not a
spanner or screwdriver, but an electronic box of tricks called an OBD scanner.
OBD or On Board Diagnostics was developed in the early 90s and since then it
has become an internationally agreed standard, adopted by virtually all major
car manufacturers. It uses the vehicle’s computer or engine management system
to log and report on faults and changes in performance. On most cars you will
find a 16-pin OBD connector mounted close to the steering wheel, under or
behind the dashboard.
These days with OBD scanners and code readers readily
available on the web for under £20, just about anyone can play at being a car
mechanic. Whilst a lot of the information they display will be meaningless to
most people, there are plenty of websites that can help to decode and interpret
fault codes. OBD scanners can’t necessarily fix faults, but knowledge is power
and having advance warning of problems can save motorists a few bob on costly
Back in the BODs before OBDs (bad old days, before
on-board diagnostics…), fault-finding was largely down to the knowledge and
experience of skilled mechanics. However, in the 1960s there were stirrings of
what was to come, in the shape of devices like this Smiths SR/D366 Automotive
Electrical Instrument Tester. Obviously it is nowhere near as sophisticated as
a modern OBD reader and as the name suggests it is mainly designed to test car
instruments, but it was part of a growing trend in the automotive industry
towards taking the guesswork out of fault detection and diagnosis.
The SR/D366’s basic test functions are for fuel and
temperature gauges but as part of that, and before the checks are carried out,
it can also be used to assess battery voltage and voltage stabiliser operation.
It’s designed to work with the most common types of gauges manufactured by
Smiths, and other companies. According to the instruction label inside the lid
these include fuel gauges that use ‘Bi-metal’ or ‘Segment’ senders, and
temperature gauges with ‘Thermal Segment’, ‘Semiconductor’ or ‘Bi-Metal’
sensors. The instruments under test are identified by code prefixes, and these
are selected using the rotary switch on the right side of the top panel. The
tester connects to the instrument or wiring using a pair of leads, terminated
in crocodile clips. The operation of the instrument is then shown on the small
meter, which appears to be based on the distinctive ‘quadrant’ family of gauges
made by Smiths and fitted to many British cars built in 60s.
Under the bonnet, as it were, it is really simple and
not too dissimilar to a regular multimeter. The circuit consists of a meter connected,
via the selector switch, to a bank of 15 precision wire wound resistors. The
instruction sheet is very easy to follow with advice on how to tell if the
problem lies with the instrument under test, the wiring or the car’s voltage
stabiliser. This is a really well made piece of kit, from Smiths Motor
Accessory Division’s Service Department, located at 50 Oxgate Lane in London.
It is housed in a smart little plywood box that is quite capable of standing up
to the sort of rough treatment it would be expected to receive in a typical
A large boot sale in Sussex was where I found this
one. The stallholder started the haggling process at £5.00 and moments later a
mutually acceptable £3.00 changed hands. It seems like an absolute bargain now,
but at the time it was a bit of a gamble as the box and its fittings all looked
a bit rough and there was no way of knowing if it worked or not. Luckily
getting it into a presentable condition wasn’t too difficult, though it did
entail a complete strip down, sanding the case and bringing the tired wood back
to life with liberal applications of good quality wax polish. There was an
accumulation of grime on the inside of the meter so this had to be taken apart,
which again wasn’t too difficult. The meter uses a bimetal strip instead of a
more common moving coil or moving magnet movement. When the strip is heated, by
a current passing through a small coil wound around it, it flexes and a simple
lever arrangement connects it to the needle. The pointer moves very slowly, and
is unaffected by vibration, which is why it was the meter technology of choice
for instruments like fuel gauges that would otherwise be jumping around every
time the vehicle goes around a corner, or over a speed hump. The meter on this
one was in good shape and the needle moved when connected to a bench power
supply. There’s not much that can go wrong with a bunch of resistors and a
rotary switch so it is safe to assume that it’s still in working order, but
until I acquire a British made car from the 1960’s fitted with Smith’s
instruments that will have to be taken as read.
By the way, the manufacturing date of 1965 is only a
semi-educated guess. There’s nothing about the SR/D366 in the history section
of the Smith’s website, or indeed any references to it on the web, other than a
tiny handful of archived sales listings on auction sites. The meter, however,
is very clearly related to those shown fitted to vehicles in mid 1960’s
catalogues and motoring magazines and is it reasonable to suppose that an
instrument to test them would have been developed at around the same time.
What Happened To It?
Smiths dates back to the early 1850s as a family run
business making watches and clocks. During the early years of the twentieth
century Smiths expanded into parts and accessories for the emerging automotive
industry then one thing led to another and by the start of World War One they
were making aircraft instruments. At the start of the Second World War the
Motor Accessories Division was split off from the rest of Smiths Industries and
in 2000 the parent company merged with the TI Group. The Smiths success story
continues and nowadays it has fingers in numerous pies concerned with
electronics, interconnections, measurement and instrumentation.
The timeline for the SR/D366 is much less clear. It’s
not too surprising, though, and given its specialist nature it is likely that
relatively few of them were ever made. It may be relevant that this one has the
number 143 written in pencil on the inside of the box. It was probably only
ever marketed through trade catalogues and magazines but how much it originally
cost remains a mystery. I’m not even going to guess, but it won’t have been
cheap and as usual clarification and corrections are most welcome. I suspect it
lasted from my estimated manufacturing date of the mid sixties to the late
seventies or thereabouts. By then it would have become largely obsolete thanks
to the demise of the UK car industry through fierce competition from overseas
companies and the appearance of more flexible and sophisticated test
instruments. Doubtless a few units have survived in the hands of collectors and
restorers, but they don’t come onto the market very often, which again suggests
that it could be quite a rare item. As far as I determine only couple have
appeared on ebay in the last few years and they went for £50 and £70; the only
other one I have seen mentioned was sold by a specialist auction house for
£150, so you know what to do if you ever spot another one in the wild!
First seen 1965?
Original Price £?
Value Today £40
Features Battery test, fuel gauge
(segment/thermal), temp gauge (Bi-Metal/Semiconductor/Thermal), Voltage
Power req. n/a (powered by vehicle under test)
Dimensions: 182 x 118 x 118mm
Made (assembled) in: UK
Hen's Teeth (10 rarest): 8