Wiring Help, 3 Problems

[ffgb]

1) On my 1981 Rabbit 1.6N/A, the PO installed a center console with 3 gauges.  These gauges are voltmeter, oil pressure, and I am guessing water temp which is in celsius. The voltmeter and oil pressure gauge work fine, but the 3rd gauge isn't working at all.  How do I know if it is wired correctly?  Where do you tap the wire into for this gauge to work?  In the engine compartment, I have an oil pressure sender that is for gauges.  One wire from the gauge is connected to it, so I know that the oil pressure gauge is working and there is another wire from the console that is connected to the front terminal of the the coolant temp sensor.  I don't know if that is correct?
2) Also, on the coolant temp sensor located on the end of the cylinder head, there are two terminals, I don't know if the PO connected these correctly.  Does anyone know what color wire connects to the front and to the rear?
3) My car had A/C, but I have removed it.  On the front of the cylinder head, the water outlet which is connected with the upper radiator hose, there are two plugin terminals.  I have replaced the water outlet with one that doesn't have the two terminals.  What are these two terminals for?  Are they for the A/C?  If they are not connected, along with not connecting the plug to the A/C compressor because it is gone, will there be any problems?

Thank You - I didn't want to start my swapped in motor and go for a drive if I know that they may be some problems!

[RustyCaddy]

I am no expert but
1) there should be a wire running from the temp sender to the temp gauge and the gauge should have a ground wire.  Also, if the gauge is something like Equus etc. but not VDO the amps (or something) will be wrong and the gauge won't work; the VW spec sender needs a VDO gauge and visa versa...which i found out the hard way 
2) i don't think it matters which sender you connect to the glow plug sender and the water temp sender can get switched around with out problems in the early MK1's anyways
3) i think the AC sender is for the AC cutoff switch for when the cars motor starts overheating...but someone else out there know better than i do.

Hope that helps

[ffgb]

Thank you for the reply.  I do have a VDO gauge, I guess the gauge is out of service.  As for the two terminals that should be on the water outlet, I guess I'll run them not connected, because the water outlet doesn't have a location for them to plug into because the motor that I transplanted in was from a 1984 without A/C.

[ffgb]

Have a question about the oil pressure.  I guess the stock oil pressure system is just an idiot light on the dash.  Right now, I am running a VDO oil pressure gauge with the $60 oil pressure sensor that attaches to the head.  From the research that I have done, I have heard that the idiot light on the dash and buzzer with not work anymore because of the new oil pressure sensor, something to the effect that the oil pressure sensor that I have are for models that have the dynamic oil pressure system, and that my 1981 Rabbit doesn't have this system.  Please explain.  Should I disconnect it and just rely on the idiot light? It's hard to drive and view the oil pressure gauge at the console, I like the idea of some sort of light and buzz sound coming from the instrument panel alerting me while I am driving .

[Vincent Waldon]

Yes, the stock system is just a simple switch... hey, they call it an "idiot" for a reason I guess.  

I personally agree that having both a gauge and a warning light is a good idea. To run both you have two options:

1) Use a metric M10x1 tee to plumb in both your old sensor switch and your new oil gauge pressure sensor to the hole in the head where the old sensor switch used to be.

2) Buy a pressure sensor that has both a sensor to drive the gauge and a switch contact for the idiot light.  VDO #360-006 is an example of a 5 bar / 80 psi sensor that also has a switch contact for your dash idiot light.

[ffgb]

Thank you for the fast response.  I do have the dual pressure sensor 80psi.  My concern is the terminal for the idiot light.  Will it have the correct voltage/resistance for the idiot light to activate?  The reason why I ask is because I thought that these dual pressure sensors were for the oil pressure systems that had the sensor on the oil filter flange and on the cylinder head, possibly different resistance and instrument cluster electronics? My car originally came with only one sensor and that was located on the cylinder head.  The previous owner installed this dual pressure sensor and discarded the original.  I really don't want to install a tee and purchase another oil pressure sensor if I don't have too.  Do you know at what oil pressure the idiot light activates on a 1981 Rabbit?  Also, how would I accurately check for that pressure, ie., activating the light at or below that pressure?

[Vincent Waldon]

The switch contact is just a simple bridge to ground, so no worries about voltage or resistance.

The trip pressure is going to be something in the range of 5-10 psi... it varied a bit from year to year, model to model, turbo or no turbo.   You could test it with a very accurate test jig... pressurize it to 10 psi and then slowly drain the pressure until the contacts close.

Having said that... my opinion is that the actual trigger pressure of the idiot light is not that important, particularly if it's just backing up a gauge.  It's really a "I don't have pressure" warning light... so having it come on at 6 psi or 7 psi probably makes very little difference.  Again, IMHO.

What *is* important is the polarity of the switch... normally open or normally closed.  The switch on the head is normally closed and opens when at least 5-10 psi is reached... so if you replace that switch with a dual contact sensor the switch contact on the new sensor should also be normally closed.

IIRC the #360-006 has the correct switch polarity to be used on the head and opens at about 7psi... but of course the VDO web site's documentation is broken at the moment.  

Holler if any of the above makes no sense!

[ffgb]

Thank you for an awesome response.  Can you answer this one, if the two plug in terminals that normally attach to the front water outlet housing on the cylinder head is disconnected because it no long exist, will this effect anything, like as in temperature readings?  Should I leave the two wires that normally connect to this water outlet separate or connected to each other to complete the circuit?

Thank You

[Vincent Waldon]

No worries.

Without seeing an exact picture I'm guessing... but what you are describing is likely the high-temperature cutout switch for A/C... if you don't have A/C these wires are safe to leave disconnected.

[ffgb]

Cool, thanks!