electrically challenged question about switch amps

[First_Ford]

The five terminals are the different taps. they give you 5 different ohmic values. 1 and 5 will be the full range and either one and another terminal will give you some portion of that full range. you can use an OHM meter to test what they are and vary the dial if you don't have something that tells you. I would test them anyway to make sure what it is.

[dc4]

Originally Posted by ZeroOne

Here ya go.... see you back here in a few days! LOL

Potentiometers (Beginners' Guide to Pots)

HA how true
I did this before reading the beginners guide to pot
I was able to get a diff potentiometer(this one had 3 poles). After installing it I realized that I didnt use the Gray/violet PTO_GND but it still worked i was ablle to to adjust my rpms. After pulling my dash apart again I tried putting the gray/violet wire on the only pole availible on my potentiometer, well something happened and my rpms shot up to 1800 i dont know if i let one wire touch the other or what. I was doing this while the truck was running. Even taking the parking brake off didnt lower the rpms. turning the engine off for a few min did the trick. Then I realized that there wasnt any leads on the potentiometer labeled as a ground. Is this something that needs to be grounded. It worked fine without the Gray/violet wire hooked up i just dont want to screw anything up by not using it if i have to.

[ZeroOne]

Originally Posted by dc4

HA how true
I did this before reading the beginners guide to pot
I was able to get a diff potentiometer(this one had 3 poles). After installing it I realized that I didnt use the Gray/violet PTO_GND but it still worked i was ablle to to adjust my rpms. After pulling my dash apart again I tried putting the gray/violet wire on the only pole availible on my potentiometer, well something happened and my rpms shot up to 1800 i dont know if i let one wire touch the other or what. I was doing this while the truck was running. Even taking the parking brake off didnt lower the rpms. turning the engine off for a few min did the trick. Then I realized that there wasnt any leads on the potentiometer labeled as a ground. Is this something that needs to be grounded. It worked fine without the Gray/violet wire hooked up i just dont want to screw anything up by not using it if i have to.

Whoa.... it went up to 1800 with no parking brake? That's not supposed to happen. I'm no expert, but reading the pdf was pretty clear on what to hook up unless we're missing something. The only think I can think of is that you don't have the connections to the right leads on the pot. Sounds like you may have ended up letting the +5v and ground short.

Did the pot come with a diagram or labels on it? From the info in that potentiometer link, the center should be the "wiper" (terminal 2), with terminals 1 and 3 on the left and right. Matching that up to the ford PDF, puts the ground (PTO-GND, gray/violet) on terminal 1... then the power source (PTO-VREF, white/brown) on terminal 3... and the variable (PTO-RPM, green) should be in the middle on terminal 2 (the wiper). Is that what you did exactly?

To be honest, I'm not even sure why it needs a ground if the truck is designed to use a simple resistor between the RPM and VREF. I would think the pot is acting like a resistor when you only used those two (which is how you say you got it to work).

EDIT: on second thought, I guess it does make sense. With the RPM wire on the "wiper" (terminal 2), that basically allows you to "swing" the rpm wire through the full range from grounded (terminal 1), all the way to +5v (terminal 3).