Help! Volvo 850 VDO Oil Pressure Gauge Sender Wiring ?

warmblood58 · Post by **warmblood58** » 29 May 2016, 14:08

Hi, I have a '95 850 T5-r where the PO added a 3 gauge pod pack and had it "professionally" installed by some shop. Car has not registered oil pressure on VDO gauge since I have had it (It has always been pegged to the right past 180) and today decided to look into why. I discovered that one of those clip on terminal connections had been used (the type that pierces the wiring insulation to make contact). I discovered that the wire connecting to the oil pressure sender unit lead wire via the clip on terminal(for the VDO unit) is disconnected which explains the pegging. Is this a ground wire typically or a hot wire? I have played around with aligator clip on leads to test and am getting either 0 psi or pegged?? Not sure what is going on? I am assuming that the PO left the shop with a working VDO oil pressure gauge and at some point, the VDO wire fell off the clip on contact connection so hopefully reconnecting the correct wire will work. There are two mystery wires, both red that are an obvious new run, one has a fuse added so I am certain that lead is hot - where would the other wire connect to, ground? Also, thinking about removing the sender to ensure good ground - what size deep socket do I need? BIG THANKS!

Post by **BEJinFbk** » 29 May 2016, 15:51

The OEM sensor is just a pressure activated switch, not a variable output sensor.
It just opens or closes a set of contacts based on a factory preset pressure.

If your stock oil light illuminates when you first turn the key to the on position and
then goes out once you've started the car, the OEM "sensor" is still there and it works.

That means that the "Professional" shop that installed the gauge set had no fracking
clue what they were doing. If you know who they are, give them a wide berth...

The way I would suggest adding a gauge would involve a tee fitting to retain the OEM
pressure switch and warning light and an appropriate variable output pressure sensor
for the aftermarket gauge. The way you've got a gauge AND a reliable OEM dash light
to let you know if you've lost oil pressure.

warmblood58 · Post by **warmblood58** » 29 May 2016, 16:08

Thanks! So find a "T" that screws into the block where the oem sensor goes and then screw oem sensor into one side of the T and the variable output sensor into the other side? Anyone know of where I can find the correct T that fits our blocks and a variable output sensor? PO was not a wrencher and paid to have people do junk like this . . . Now I am going to have to put fan housing back in and pull unit another day to get at this damn sender. Now I understand why it does not work. Thanks!

warmblood58 · Post by **warmblood58** » 29 May 2016, 17:07

My guess is the owner failed to get all the parts needed or his "mechanic" discovered missing parts and they stopped at voltmeter and boost and decided looking at a non op oil pressure gauge was all right . . . . grrrrrrr

beigg · Post by **beigg** » 29 May 2016, 21:08

that "T" is going to add up rather fast in cost unless someone now makes a simple one piece solution. I do not remember what I all used, but over five years, the cost going over 50.00 just in fittings definitely is not forgettable. Keep in mind the limited space you will be working with should you have the a/c parts still in place...

warmblood58 · Post by **warmblood58** » 30 May 2016, 08:20

Maybe IPD has something -

warmblood58 · Post by **warmblood58** » 31 May 2016, 08:28

Has anyone done this on their 850?

info2x · Post by **info2x** » 04 Jun 2016, 17:34

I added oil pressure to my last 850. I go rid of the idiot light function because I didn't like the way the T setup looked from a reliability standpoint. Was going to make a simple comparator circuit such that if the voltage output from the sensor dropped to a certain point it would activate the idiot light.

beigg · Post by **beigg** » 04 Jun 2016, 19:28

Going off memory, the block should have one spare oil gallery that could be used. Remove threaded plug and install a/m sender.

warmblood58 · Post by **warmblood58** » 06 Jun 2016, 11:20

where is the general location of the spare oil galley? Thread and pitch for this port known? Thanks!