On MK2's, 3's, 4's etc it's in the cluster.... thought it was for MK1s as well. 
EDIT: except that as far as I know, MK1s didn't have the dynamic oil pressure warning system?
my 84 has a dynamic oil pressure warning.. and its most definitely a mk1..
Is the oil warning buzzer behind the square white button at the upper left hand corner?
That would be my *guess*... looks relay-like.
On cars so equipped the buzzer is going to be on the blue flexible circuit... probably facing the driver... if so you won't be able to see it without disassembling the cluster to turn the flex circuit inside out.
IIRC its a small white plastic circular device with a small hole in its front face.
BTW... dunno about your ammmeter... but mine has an resistance of quite a few ohms when measuring mA... so may be confusing your cluster a little bit. Your other test is accurate... with the wire to the oil flange sensor dangling the buzzer and LED should come on over 2500ish RPM... if just the LED flashes it's likely a bad buzzer... if neither the LED nor the buzzer come one somethings amiss more generically.
Does anyone know whether the oil pressure alarm get the rpm signal from the alternator's W terminal?
Does anyone know whether the oil pressure alarm get the rpm signal from the alternator's W terminal?
Yup.... that's the only RPM signal available on a pre-TDI diesel.
Update: I brought out the W terminal out of the alternator (that didn't have a W terminal). It measures about 8 VAC at idle and 8.7 VAC at 2500 rpm. Buzzer in cluster didn't go off with the high pressure oil switch disconnected. So I tried a different cluster (the original diesel cluster that came with the Jetta) and the buzzer worked!
The cluster where the buzzer didn't work is a gasser CE2 cluster where I made the tach work with 2 magnet triggers on the harmonic pulley. Do gasser alternators have a W terminal or does the gasser cluster get its RPM signal from the ignition coil? I am wondering if the cluster's buzzer not working is due to its being fed an improper RPM signal from an alternator W terminal instead of from from the ignition coil? What do you think?
This is getting a little complicated. Maybe the easiest path to a high oil pressure buzzer alarm is to find a CE1 buzzer in a relay and do some custom wiring?
The gasser cluster gets its signal from the ignition system and it's about 1/8 the speed of the W terminal, so the calibration of what RPM the oil buzzer alarm wakes up will be a long ways off if you use a gasser cluster in a diesel.
The voltages of the two tach signals are also quite different, so the gasser cluster may not understand the W terminal signal on *two* fronts: voltage and frequency.
Having said that, if you're feeding the gasser cluster from two magnets and getting a good tach signal that same signal should drive the oil pressure warning system as well.. but it looks like you added the W-terminal feed?
The W terminal signal goes in the gasser cluster pin T28-10 (tach), however, the tach signal is not coming from the W terminal but from the custom mag pickup that goes direct to the tach chip input. Question with the gasser cluster is if the buzzer gets the rpm signal from the tach or does it have it's own rpm detection circuitry? The buzzer works in the orig diesel cluster that came with the Jetta, which has no tach, so it must have its own rpm detection circuit. Without a schematic of the gasser cluster, it would be hard to figure out what's going on.
a) Buzzer is contained in the oil pressure warning system relay; normally 813 919 082 (with or with out a suffix of A, B, C, etc)
b) The relay on my MK1 is inserted into a receptacle 175 937 501 B. The receptacle usually is tied off or slides into slots on the outer edge of the fuse block. HTH
Would you or anyone else have an extra relay 813 919 082 for sale? I think my easiest path to a working high oil pressure warning buzzer is this relay.
The buzzer works in the orig diesel cluster that came with the Jetta, which has no tach, so it must have its own rpm detection circuit.
The factory wiring works like this:
- the car has a source of RPM signal. On a gasser it's the ignition coil on the points/transducer side, on a diesel it's the W terminal off the alternator.
- that signal is led over the engine harness, thru the firewall, and up to the cluster via pin 10 on the cluster connector
- if the cluster has a tach, the signal on pin 10 goes to both the tach and the oil pressure warning system. If the car does not have a tach the signal only goes to the oil pressure warning system.
At least that's how it's wired from the factory. If someone has spliced in wires directly to the cluster itself all bets are off.
If you have a magnetic transducer circuit with two magnets retrofitted to your diesel car it should be able to drive pin 10 of a gasser cluster directly, thus feeding the oil pressure warning system and a tach, if the cluster is so equipped. No need for a W signal, and if you're using a gasser cluster it won't understand the W signal properly anyways.
In the spirit of a (fuzzy scope) picture being worth 1000 words:
W signal, diesel:
Tach signal, gasser:
Quote:
"If you have a magnetic transducer circuit with two magnets retrofitted to your diesel car it should be able to drive pin 10 of a gasser cluster directly, thus feeding the oil pressure warning system and a tach, if the cluster is so equipped. No need for a W signal, and if you're using a gasser cluster it won't understand the W signal properly anyways. "
Not true with the mag transducer I used, which would not drive pin 10 of the gasser cluster because of an attenuation network at the input. I had to wire the transducer direct to the tach IC input pin to get a strong enough signal. If what you say is true, the pressure warning system's tach signal does not come from a gasser tach's output but from it's input (pin 10). Since the tach works fine in the car, I have to get the tach input signal over to pin 10, but I don't know if the signal level will be sufficient.
Since the tach works fine in the car, I have to get the tach input signal over to pin 10, but I don't know if the signal level will be sufficient.
Yup, and as you say, if the signal from the transducer wasn't strong enough to drive the tach thru pin 10 it may not be strong enough to drive the oil pressure warning system either.
I suppose another approach would be to find a transducer that can drive pin 10 once and for all, rather than mess with the wiring? Hall-effect with a pull-up resistor perhaps?