[ray_mcavoy]

Originally Posted by Bmstd

ray_mcavoy... you have become my wiring mentor and hero. You were able to help me connect the dots so to speak.

After much thought and common sense applied (or as much as I have to offer) i had come to the same conclusion knowing the original oil warning light and the e-choke light was getting its feed from same connection. I was missing the diagram to help me understand that. With your help, i was able to figure out which wire in the bulkhead to re-pin,,, and now the oil gauge provides a reading.

You're welcome! Glad I could help.

Originally Posted by Bmstd

Now for the new question,,, When i shut engine off, the oil gauge stays where it was at last. Then, when I cycle the key to on position, the gauge tries to return to zero, but once it gets to the mark by zero, it then stops for split second and bounces to the 3 o'clock position and stays until i start the truck. I have rechecked the ohm readings on the oil pressure sending unit and do get a 0Ω reading with engine not running and do get 51 Ω reading when engine is idling.

The part where the gauge stays at it's last reading when the engine is shut off is normal. The electric oil, temp, and fuel gauges use an air core meter movement that positions the needle using a couple of perpendicular electromagnetic coils. When the power is switched off, there is no magnetic field to position the needle so it either stays in it's last position or might move one way or the other due to gravity.

And obviously, the gauge wanting to return to zero with the key on, engine off is normal as well. But having it bounce back to the 3 O'Clock position is definitely unusual.

The resistance readings from your oil pressure sending unit appear to be normal.

Originally Posted by Bmstd

To add to this, the original trucks wiring for bulkhead to the cluster (warning lights) is lacking an additional 12v positive lead and and addtional ground lead. I ran extra lead for ground wire and used the bulk body ground terminal on drivers pillar (under dash) as ground source. for the addtional positive lead for now I jumped power from #3 location at cluster to #6.

Did you mean to say you jumped power from #6 to #4 (instead of #3). On the 76+ gauge clusters, #3 should be ground for the voltmeter and #4 should be switched ignition power for the voltmeter. As you discovered, both of those wires need to be added when converting from lights to gauges. Jumping them over to pre-existing power & ground wires on the cluster plug is perfectly acceptable. In fact, if you were to untape an original gauge type harness, you'd find factory splices in those wires that branch them off to the multiple locations on the cluster plug.

Originally Posted by Bmstd

Is this a case of damaged oil pressure gauge or possible wiring (ground) issue?

It could possibly be a problem with the gauge but I have never seen one exhibit that sort of behavior. To verify the wiring, you can remove the lens and front tin from the cluster (leaving the rest of the unit still in the dash & plugged in). With the front off, you can remove the oil pressure gauge and hook a multimeter (set to DC volts) up to the cluster terminals that provide power & ground to the oil gauge. Then monitor the voltage to see if anything strange is happening when you cycle the key and leave the key on with the engine off. Similarly, if you connect the multimeter (set to ohms this time) between the cluster terminals that provide the ground & sending unit connections to the oil gauge. If the wiring is okay, you should get readings that are very close to the ones you obtained when measuring the sending unit directly.

Originally Posted by Bmstd

My goal is to go to local salvage yard and pull all the correct color wires with correct terminals from a donor vehicle and add to my existing dash harness. I am a bit OCD when it comes to doing conversions and want to have this correctly wired as GM would have done. I will be pulling and adding a single pink/black for 12v positive, black for ground and dark blue for e-choke light. This just sounds more simple that pulling a whole harness from an original gauge truck and swapping into this one. That and there are plenty of gutted out truck with dash wiring left.

I'm the same way when it comes to wiring ... I try to keep with the "factory correct" theme of wire colors, terminals, and such whenever I make modifications or repairs. Pulling & swapping the entire dash harness really isn't all that difficult. But there were some year-to-year differences so finding an exact match to what you need might not be easy. Your plan to extract the necessary wires/terminals from a donor harness and install them into yours should allow you to make sure everything matches the specific needs for your truck.

Originally Posted by Bmstd

1.) Please let me know your input and thoughts on the oil gauge still returning to the 3 o'clock position when key is on?

As I wrote above, I'm not really sure what is causing that. Removing the gauge and taking measurements at the cluster's oil gauge terminals should help determine if it's a gauge or wiring problem though.

There are a few places in the cluster's circuit design that are subject to poor / loose connections. Namely the cluster plug terminals and printed circuit traces they make contact with. Along with the metal clips that make the connection between the printed circuit traces and the studs on the back of the gauge. And the nuts that secure the ceramic resistor to the back of the gauge. A problem at any one of those points can prevent the gauge from operating correctly so those would be worth checking.

Originally Posted by Bmstd

2.) Also would it be possible to send me a copy of wiring diagram and pin position for wiring at the bulkhead and fuse box so i can also make sure all my pin positions for both positive and negative between bulkhead, fuse box and cluster are also in correct positions? I want to leave nothing to chance.

Thanks to fellow member hatzie, you can download PDF copies of the GM wiring diagrams here --> http://67-72chevytrucks.com/vboard/s...d.php?t=545416