47-55.1 Help from smarter people

[Matt_50]

I bought some VDO gauges and I'm a little unsure how to hook up the oil pressure gauge.


Gauge itself looks easy enough. "T" for the sender wire. "B" for 12volts. And ground symbol for ground.

My question is with the sender. It has two tabs on it. There's continuity between the two tabs but none between either tab and the case.

Do I wire both together and then to gauge?

Do I use only one tab?



AND, is my oil pressure sender above my oil filter? Ifs so it also has two tabs... I have another sender of some sort on passenger side of block too, no idea what it is.

[Matt_50]

And yes, it came with instructions but only for the gauges.

[dsraven]

I think one terminal (wk) is for a warning light on the dash and the other(G) is a signal wire for the gauge. that seems to ring a bell from my vw rail buggy days. the sending unit needs to be grounded as well as the dash gauge does. the sending unit isn't usually a problem with grounding because it is mounted to the engine (usually) but sometimes the dash ground part gets a poor ground through the body so the gauge reads wrong or is jerky. remember to have a dedicated ground from the body to the frame to the battery. clean bare metal, attach the parts with star washers under the screw or nut heads, test, then coat with primer or some other rust preventative. I have used a bus bar style of connection under the dash where all the grounds can find a home with a screw terminal location for each one. less chances of having a ground issue that way. a bus bar style terminal strip should be pretty reasonable as well. the wire that feeds the bus bar can be run directly from the battery or from a good ground source other than the body. sometimes I will run a battery ground to the body and connect the bus bar feeder wire at the same location.

[dsraven]

the other sender on the side of the block, passengers side, looks like a knock sensor. they usually plug the block drain hole and have a single wire going to them.
does it look like this?

https://www.amazon.ca/ACDelco-213-32...61034537&psc=1

[Matt_50]

If you can see it in the first picture, the tabs are insulated from the sender body. I didn't get a ohms or continuity beep when I went from a tab to the sender.

[Matt_50]

How does a knock sensor work on a carburated engine?

Is there a way to wire my gauge and sender up and test them? So I could test if I need to ground one of the terminals?

[dsraven]

oil pressure sender on the gm small block can be behind the distributor or above the oil filter (and some old engines have a spot in front of the intake manifold above the timing cover). either or and some use both spots if fuel injected. one runs the gauge/light and the other feeds info to the ecm i think. also may be used for a fuel pump relay cut out if oil pressure is lost.

[dsraven]

the dizzy would need to have a module that supports a knock sensor. usually has a big plug in on it and the donor truck would also have a large plug on the firewall that went to the ecm or esc unit in behind the glove box. esc stands for electronic spark control unit. basically the knock sensor is a pezio electric device so it makes a small current when there is a knock in the engine. this signal goes to the module and the module retards the timing and then starts to advance the timing until it senses input from the knock sensor and it all starts over again. I think they only used esc for a couple years and then the throttle body injection started, basically using the same type of system but with injectors instead of the carbs and a separate esc unit mounted on the back end of a valve cover instead of inside the dizzy.
on these systems you can run a timing light and use a small hammer on the running engine block next to the knock sensor to simulate an engine knock. the timing should retard when you use the hammer lightly. if it doesn't work then there is a problem with the system. it if does work but you had timing issues before then the knock sensor is usually at fault.

[Matt_50]

This rings a bell. Shortly after I got my c10 after high school I had issues with the distributor. 2nd time I had a problem I took it to a mechanic.

Apparently wires were shorting out behind the engine when they got wet with oil, had a valve cover leak.

Anyways, the mechanic pulled out a small bundle of wires that a OP had undone and left back there. They ran to a black box/module. The mechanic said it was like a very early computer. Since it was disconnected, he took out the wires, and the little box. He also put in a different distributor, he said it was a older style.

Several years later and no issues. Does this sound like what your talking about?

[Matt_50]

Back to my sender... do I use just one of the tabs?

[dsraven]

yeah, sounds like the esc unit was giving issues and the mechanic just took the system out and installed a standard old fashioned dizzy that works. you probably have some other extra wiring in the loom that isn't required and the oil pressure sensor with the 2 prongs could be for that as well. did you also have an electric fuel pump or a mechanical one on the block?

[dsraven]

if you only have a gauge and no idiot light for low oil pressure then yes, use a single tab. the G tab should be the gauge tab. the other would be for the idiot light. it is hard to see in the pics, are the tabs labelled?

[Matt_50]

mechanical. So the two prong sender above the oil filter is the oil pressure sender?

[Matt_50]

Nope, no labeled.

[dsraven]

idiot lights aren't such a bad idea. we don't always drive around with our eyes glued to the gauges, right? that's why they were installed in the first place, well, that and cost prolly. If I were you and had a spot to put one in i would. can't hurt right?
you can easily test which tab using a test light. connect it similar to the circuit you are copying. power the light and touch the tab on the sender-engine off. if the light turns on then that will likely be the idiot light tab because the idiot light would be lit when there is no oil pressure. if the light comes on with engine running then that would be the gauge tab. light may get brighter with the engine revved up some because the ground is variable depending on the oil pressure.

[dsraven]

the 2 pronger is usually an oil pressure switch for cars that had an idiot light.
does it look like this?
https://www.opgi.com/monte-carlo/L241018/

[Matt_50]

Do I need a fuse? Could I piggyback power for the light off the gauge? Then the ground wire runs to the sender tab?

[dsraven]

the other location that is most common is behind the dizzy. if you have headers that may be a better place so the wires and sender don't get cooked so easily. there are other wires up there anyways so the oil pressure sender wiring can piggyback in the same loom out of sight.

[Matt_50]

Third pic is the one above oil filter. Kinda looks like your link. Are all oil pressure sending units kinda bulky like in my first pic.


If I run a light and test the tabs... if they have continuity between the... won't both light up?

[dsraven]

if you are gonna piggy back power from the gauge to the light I would not connect it right on the back of the gauge because it could affect the gauge working properly by stealing some power and causing a voltage drop there. if the fuse panel is close simply run a fused "key on" wire up to the light, through the light, then down to the sender for the ground (so the bulb doesn't get a ground in the dash, or it will be on all the time. it uses the sender for the ground).
when I build rail buggies I use a similar idiot light set up. I use a large red trailer light in the middle of the dash so nobody in their right mind could possibly miss the light when it comes on. you could do something similar if you don't have room in the cluster for the idiot light. use an indicator light for a PTO or some other remote mounted indicator light. might look a little weird though. you can also wire in a buzzer under the dash or in the fuse panel that would do the same thing and make you look at the gauges when the buzzer sounds. like seat belt chimes used in cars or key left in ignition chime. prolly cheap at the wrecker and not in your cluster if you want to keep it clean looking.

[dsraven]

maybe go to the vdo site with the part number off the sender and see if there is a wiring diagram for the sender you have, just to be sure you get things wired correctly.
also, don't use teflon tape on the threads when you install,it interferes with the ground circuit and also has a tendency to string off and get little pieces into the oil gallery.

[dsraven]

can you get a better pic of the sender including the part number? or did the kit come with the part numbers included so you can use that to find a wiring diagram?

[dsraven]

check this site for some info. maybe find a part number on your sender that matches something on this site and then go to downloads for the instruction sheet.

https://www.vdo-gauges.com/media/ins...%20Senders.pdf

[dsraven]

https://www.vdo-gauges.com/sensors/p...g-contact.html

[Matt_50]

Went outside to check for a sender by the dizzy... and this is why this thread is titled the way it is... the sender is behind the dizzy!

So... above filter is for the idiot light.

And the passenger side is a knock sensor that I guess I can ignore.