1976 oil pressure gauge wiring

[kavadarci]

Hi,
I'm trying to figure out if my wiring for the oil pressure is correct as it never worked before.
i am 90% sure my sender unit is bad also and while i'm waiting for it i want to make sure my wires are correct as someone changed some wires with non factory color coded wires.

This attached picture is from another gauge but mine is the same.
I'm again interested in the one on the left on the photo as when i connect as pictured i get my wires hot and if i hold too long i think they will melt.
if i connect the other way around the gauge jumps to maximum but i have no signal from the sender (which again i think it's defective).
I would greatly appreciate your feedback and possibly guide me to a wiring diagram that can help me further.

[timmy2]

Connect it at the gauge so it goes to full deflection.
Lift the green/red wire at the sender and then ground it to the engine. the gauge should go all the way through it’s range when you lift off of the ground and then ground it.
That proves the gauge is good.
The “signal” is just the gauge reacting to the amount of resistance to ground at the sender.

76 wiring diagrams.
https://www.dropbox.com/sh/r34ab8n9hx7xl02/AAArayQGr-klXXq_HeUG65cKa?dl=0

[kavadarci]

Amazing info.
I have to admit I am not good at reading these diagrams so if not mistaken oil pressure gauge is G11 on track 85.
Green and red wire goes to one side snd the red and black (power 12v) goes to the other.
When I look at my gauge there is one more plug which I thought it’s for ground.
Is that true and if yes why is it not on the diagram or again, i am just not reading it correctly?

Thank you so much.

[timmy2]

For whatever reason during the change to current flow diagrams from well laid out schematics, Porsche stopped drawing in the grounds in the gauges. maybe as they assume you would have all the earlier wiring diagrams in the service manuals...
This link to a 1970 schematic is worth looking at for the old style drawings at the gauges.

https://www.dropbox.com/s/32266dstkfqnwrx/SL35-Master.pdf?dl=0

[kavadarci]

Ok, thank you so not loosing it here, :-)
One final question if you don't mind:
From the diagram can one tell which side of the oil pressure gauge is signal and which is 12v as opposite connections will sure fry something. It's kind of important information and wondering if one can read that from the diagram.

Thank you.

[timmy2]

All indication is on the VDO gauge for connections.
For your year the red/black wires (originally) are gauge power. The signal wires are as in the drawing for each device. Green/red for oil pressure gauge, green/white for oil pressure switch ( aka idiot lamp) etc.

[timmy2]

The only gauge that shows polarity (+) is the Tachometer on the 77 drawings.
Porsche hid the clues...

[timmy2]

There is a post somewhere on here describing how the gauges are physically built comparing them to a Wheatstone bridge. So yes, polarity matters as the reversed connection will go to ground in the balancing leg. Likely why your wires got hot!

[kavadarci]

Originally Posted by timmy2

All indication is on the VDO gauge for connections.
For your year the red/black wires (originally) are gauge power. The signal wires are as in the drawing for each device. Green/red for oil pressure gauge, green/white for oil pressure switch ( aka idiot lamp) etc.

I can only see the ground symbol but nothing else?
No indication to tell me which is 12v and which is signal.

[911 SLANT]

Ok, now can somebody explain the oil level gauge. Mine is not working after installing new sender in tank.

[stevie 77 930]

Originally Posted by kavadarci

I can only see the ground symbol but nothing else?
No indication to tell me which is 12v and which is signal.

There is actually a little + on the hot side for each gauge I can see it in your pictures
If wired correctly, and your wires get hot, it generally means you have a short on the hot side. Trace from there as the red w/ black piggybacks on all of the gauges

Oil pressure gauge electrical connections.......

[timmy2]

Originally Posted by 911 SLANT

Ok, now can somebody explain the oil level gauge. Mine is not working after installing new sender in tank.

Maybe give this a read?
Oil level gauge troubleshooting

[kavadarci]

Originally Posted by stevie 77 930

There is actually a little + on the hot side for each gauge I can see it in your pictures
If wired correctly, and your wires get hot, it generally means you have a short on the hot side. Trace from there as the red w/ black piggybacks on all of the gauges

Oil pressure gauge electrical connections.......

Ok, i'm getting closer and closer. It has to be with the short on the hot side.
but wouldn't that cause the other gauges not to work?
the temperature works fine and the lights work fine BUT the turn signals on the next gauge (speedo) don't work.

Ok, i think i need the wiring for the hot but isn't hot hot hot no matter how its wired or piggy backed?

Thank youuuuuu

[kavadarci]

Further work done.
My “signal” lines are ok but my power wires have been manipulated.

What I don’t understand what is the difference between the red wires with black lines and the black\red solid lines?
Does it also matter how the power wires go into the oil level first and then to the light to the oil pressure as my double plug wires are on the first connector and should be second.

I would appreciate further feedback on how the power wires are connected properly.