Re: Dim oil pressure warning light

[Tim Buja <buja@domain.elided>]

Peter Howells wrote:
>Hi all
> I think the oil warning light is always dim during the bulb test, on
> ignition switch on.
> I think it is unlike the other warning lamps in that it is wired in
> series with another bulb namely that of the Brake warning lamp. Also
> looking at the wiring diagram, it seems to me that when the oil
> pressure warning light is on due to low pressure, then the Brake
> Warning light must also be on although not at full power. 
> Also, if the oil warning lamp bulb is shot, I do not see how the
> Brake Warning amp can show at ignition switch on because it needs the
> Oil pressure warning bulb to complete the circuit.
> I am looking at the wiring diagram for cars up to LD 20000.
> It seems to me to be a strange layout.

You are correct, if the oil pressure light is burned out the brake
light will not come on.  Also, if the brake light is burned out, the oil
pressure light will not come on.  This is the purpose of the bulb check
function - to allow the driver to verify that the bulb(s) are working.

The oil pressure light will never light up at full brightness since it
always has the brake PDWA warning light in series with it.  The brake
PDWA light will light up at reduced brightness with low oil pressure, and
full brightness with a PDWA activation.  The same circuit is on the post
20000 cars, as well.

"Strange" does certainly apply in this case!

Robert Ducker wrote:
> It sounds strange, but if you use a higher wattage bulb for oil
> pressure, it's brightness will actually go down, so try to get the
> exact replacements for both brake and oil bulbs. Another option may
> be to increase the wattage proportionaly on both bulbs at the same
> time (haven't tried this). This setup is similar to most cars of the
> era. 

I wasn't suggesting a higher wattage bulb, but a lower voltage bulb.
The oil pressure light in the warning cluster will never see full
voltage since it is always in series with the PDWA bulb, so it will
never produce full brightness to get your attention in time.  A lower
voltage bulb of the same wattage should do the trick, if it were
available.

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