Dim oil pressure warning light

[Tim Buja <buja@domain.elided>]

David Horsnell wrote
>>Also whilst I'm connected, thwe oil warning light on the car is
>extremely dim (unable to see in anything other that total darkness)
>despite swoping the bulb with others in the warning cluster.  Could it
>be that only the circuit through the brake system warning light is
>working (as the wiring diagram seems to suggest that they are
>connected)and that the oil pressure switch is dead ?  Any
>thoughts/comments greatfully received.

Same as mine was when it was running.  (I'm going to the engine shop
today at noon to pick it up!)  I'm not sure about the UK wiring, but for
US cars, our Federal Government requires a "bulb check" so the driver
can verify that all the warning lamp bulbs are functioning before
starting the engine.  When the ignition switch is turned to the "run"
position with the engine not running (on initial startup, usually), all
the lights should come on.  The bulb check function for the "ignition"
light is controlled by the alternator voltage regulator, which should
turn the light off as the alternator comes up to speed and starts
producing voltage.  The current supplied by the ignition lamp is
required by the regulator to provide the initial field excitation.  If
this lamp is missing or the wrong size, there will be insufficient
alternator field current and the alternator will never produce enough
voltage on startup to power itself (or anything else).

Here's an example:  I had a VW dealer tell me that I had to replace an
alternator because the charge warning light would not go out.  The real
problem was that they put a smaller wattage bulb in that warning lamp.
The reduced current to the alternator regulator was insufficient to
allow the alternator to self-excite itself, and the light would never
go out.  Replacing the 1.1W bulb with a 2.2W bulb fixed the alternator
"problem".  Back to the original topic...

The bulb check function for the brake warning light (PDWA) is supplied
through the oil pressure switch, as these are wired in series to
provide the bulb check function.  According to the owners manual, both
the oil pressure and brake warning lights will glow for low oil
pressure, and the brake warning light will glow brighter for a PDWA
activation.  My TR6 has the same circuit for the PDWA bulb check, but
the brake warning light is in a better location (above the speedo &
tach) so you really notice it when it comes on with low oil pressure.

I suppose that you could increase the brightness of the oil pressure
light by installing a 6 volt bulb, but these don't seem to be available
in the size required for the warning cluster.

I've noticed that in bright sunlight and with the top down, it is
impossible to see the low oil pressure light should it come on.  It is
for this reason that I am installing a oil pressure gauge.

A mailing list hint for Compuserve users:  I've found that it's much
easier to read mail I send to the list when I restrict the line length
to 72 characters.  If you don't, Compuserve will put an equals sign at the 73rd character and
wrap the remaining text to the next line (like these two lines.)  When composing your mail to
the list, click on "Options" (or hit Alt-O), then click on
"Send exactly as shown" (or hit S).  As you enter your message, hit
the <Enter> key before you get to the 72nd character on each line.
This will prevent the word wrapping and your posting will be much
easier to read.

Tim Buja - Rockford, Illinois, USA - 80 TR8, 73 Stag, 72 TR6