911 oil temp/pressure guage, need wiring help Options

[Trekkor]

I have the guage in the car and the temp side is wired.
It's the pressure and idjit light that I need help with.

New wires are run from the senders to the guage.
What wire goes where?
I have four wires. One off the idiot sender and three off the pressure sender.

Help me help myself. (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif)

[lapuwali]

QUOTE (trekkor @ Mar 2 2005, 10:45 AM)

Soooo, in my pic, let's say the white is ground and the red is 12+ jumpered from the dash and the black is sender signal? May not be that way in the pic but that's the idea? Green is obviously attatched to the idiot sender. Does it wire to the indicator light on the guage with the other side 12+?

The idea is that the idiot light has +12 on one side of the bulb, and the other side is grounded through the sender. The sender here is just a switch that OPENS above some set pressure, and closes below that. The gauge is similar, except the ground is through a variable resistor that changes resistance (to ground) based on the pressure. The gauge needs a separate "real" ground to act as a reference so it knows how far the pressure sender "ground" is from the "real" ground. The difference is displayed on the gauge.

In the two-post VDO sender, one terminal is for the light, one for the gauge, and the ground is through the threads in the sender into the engine block.

This oddball sender COULD have a separate ground wire, rather than grounding through the threads. If that's the cause, then one post will be light, one will be gauge, and the third you just ground somewhere. It also COULD ground through the threads and the third wire is +12, which is used by some active device inside the sender. As I said, I've not seen one of those senders, so all I can do is guess.

You could try measuring this sender to see what's what. See what the resistance is between pairs of wires (three ways to do this). If one wire is a ground wire, then you'll probably get 0 ohms between two wires and something above 0 between two others and infinite between the last pair. The pair with 0 ohms are the ground and the light switch. The pair with something above 0 are the ground wire and the pressure sender, and the last are between the light switch and the pressure sender. If you think you've got a handle on that, try starting the engine and see how the resistances change. The light/ground wire pair should now show infinite (switch open), the pressure/ground wire pair should show something other than what you measured with the engine off, but it shouldn't be 0 or infinite. The last pair should still be infinite.