Aftermarket Gauge troubles

Hello group. It's been a while since I've posted but new problems seem to crop up. I have installed a trio of aftermarket gauges to monitor
engine activity out back. Following the manufacturer's instructions has been a bit troublesome. Engine is currently not firing (intentionally) while I try to test oil pressure gauge. I got the handy oil pressure gauge with the idiot light and pressure sensor all-in-one. The Speedo lights are wired hot just like the regular idiot light. Generator light works just fine. Tested the OP bulb and it lights. Oil pressure Idiot light does not light. I am reading 12V at the oil pressure switch out back so I thought it was a grounding issue. Ground strap is tight. I can make the OP light work by removing it from the sensor in the case and grounding it to the alternator nut with alligator clips. What gives? If I am pulling 12V from the front of the car why wouldn't the OP sensor ground to the case? There is obviously a fundamental element I am overlooking so maybe a fresh set of ears can help out. Thanks for any help. At this point it IS appreciated.
PS. I do have oil pressure b/c I removed the sensor and cranked the engine. It is pushing oil through. Engine was recently re-installed but I haven't tried to fire it until I work this bugger out.
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You didn't use teflon tape to seal the OP sender did you? Doing so will break the path to ground for the sender.

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Hey Erik. No Teflon tape was used as per manufacturers instructions. I am truly at at a loss on where I am losing the ground. I can ground to the Alt. nut and to the carb linkage but absolutely nothing to the OP sensor. Truly Bizarre. I read 12V at the idiot light side of the sensor and 8.58V at the OP gauge side of the sensor. The problem is definitely not in the wire to the front as its been ruled out as ok. I'll have to throw the old OP switch back in and suss out whats going on.

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jtbartlett wrote:

Could it be that your ground path from the sensor to the gauge is too high? I ask because of the sensor only has a range of a couple of ohms and the ground resistance is a couple of ohms, it will introduce quite a bit of error. Perhaps temporarily try bridging the ground from the sensor to the gauge to see if it starts working. If so, you may have a grounding problem somewhere.
Remco
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with the new Oil Pressure Sensor in place, are either terminals "grounded" with no oil pressure? The "switch" terminal should light up your 12V test light brightly while the sensor terminal will only create a dim light.
Are these VDO items? I ask because I seem to remember that there might be a similar sensor on some Audis where neither terminal is "grounded" with no oil pressure.
JMHO but it sounds like the sensor is not correct. later, dave (One out of many daves)

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Thanks for the replies. What is really bothering me is the fact that my Alternator light grounds A OK but the OP side of the sensor in the case doesnt seem to. I can bridge the ground with alligator clips in two ways and activate the light: at the sensor itself to the alternator, and at the bulb in the speedo to a ground in the trunk. I have 12V at the bulb and at the sensor. These are not VDO gauges but I believe they should operate in the same manner......right? :) I CANNOT activate the light by grounding from the sensor to the trunk ground.
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so did you run an extra wire back to the engine from the aftermarket oil pressure gauge? I will assume that you did so the original wiring should be untouched and the original idiot oil light switch system should work.
Or describe exactly what you have? Original Speedometer with Idiot Lights operatiing Additional oil pressure gauge, new wire to the new dual OP sensor. OR Non original Speedometer Aftermarket Oil Pressure Gauge Aftermarket Oil Pressure Idiot Light New Dual OP Sensor.

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Here's what we have: Non original speedo, it is a VW Speedo with working Idiot lights, just not original for the year. Original wiring harness is intact, correct wiring for the idiot light and pressure sensor in the block. I had to run 2 wires to the rear, one for the pressure side of the switch and one for an oil temp sensor in the case.
I removed the aftermarket sensor and plugged in my orig. pressure sensor. Everything works as it should, idiot light on with key and turns off when it cranks. So...there's no problem there. The problem must be with the aftermarket OP sensor. I removed a rubber plug to look inside the sensor. Everything looks like it should. Copper contacts are in 'closed' position. The only thing I can come up with is the size of the oil pressure 'hole' in the sensor. the aftermarket hole (where oil enters the sensor) is considerably smaller that the original VW sensor. Prehaps if all else fails i can drill it out to a similar size. I can't see how it would make a difference as long as oil is entering the sensor it should be the same pressure. So.. thats where I stand. If anyone know of a different 'kind' of OP sensor, that is, if there are indeed sensors that work mechanically different, please drop a line here. I've never heard of such a thing but that's not saying much! Thanks.
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