Re: USA Urq Oil Pressure Monitor

[ejfluhr@austin.ibm.com (Fluhr)]

> Eric,
> Not sure I get this.  The coupe GT sender has two connections, one for 
> the gauge and one for idiot switch, or so I thought.  I plumbed my dash 
> light, and I assume warning right into the GT sender on its aux post and 
> it has been functioning properly, displaying low/no pressure right after 
> oil changes and the like, while the guage does its thing.
> Mike

Mike,

You are correct in your description of the GT oil pressure gauge sending
unit.  One connection is the output for the pressure gauge, while the
second connection is [supposed to be] a high-pressure (1.8bar) switch.

According to the schematic, the original urq wiring has the relay socket
for the oil pressure control unit and the wiring is the same as that
for the Coupe GT control unit.  However, the Coupe GT uses two pressure
switches, one high and one low.  In the Coupe, the dash light can be
activated by (1) the low pressure switch making contact to GND if the
oil pressure drops below 0.3bar, (2) the high pressure switch breaking
contact with GND above 2000rpms, as determined by the control unit.

The urq comes from the factory with only the low pressure oil switch,
and this is connected to the **high pressure switch** wire in the
wiring harness.  The relay socket has a jumper on it that connects
the low pressure switch to the dash bulb output.  When the oil pressure
is below 0.3bar, the switch is on (shorted to GND) and the dash bulb
should illuminate (a good way to check this is to verify that the oil
warning light is on when you turn the ignition on but do not start the
car...i.e. oil pressure is zero).  When the oil pressure is above 0.3bar
(which should be all the time except in the event of a serious failure),
the switch is open and the dash bulb stays off.

I do not know why your oil sender/light is working correctly, unless
the switch in your sending unit is broken.  The switch on the sending
unit operates in the opposite manner from the low pressure switch; the
high pressure switch is open at pressures below 1.8bar and shorted at
pressures above 1.8bar.  If you just connected the urq wiring from
the old low-pressure switch to the high-pressure switch on the sending
unit, you would need a control unit in the relay socket to make it
work correctly.  At least, I made this conclusion from studying the
wiring diagram and making the change on my '82 urq.  Perhaps something
changed in later model urqs.

(This is from memory, so I may have made a small mistake in some of my
descriptions.  Most of it should be accurate, however.)

Later,
Eric
'85 CGT, '82 urq
---
Eric J. Fluhr                                Email:  ejfluhr@austin.ibm.com
630FP Logic/Circuit Design                   Phone:  (512) 838-7589
IBM Server Group                             Austin, TX