How does the circuit board work?

[99ss]

How does the circuit board and gages work? I have a rallye dash I was going to put in. I have a new wiring harness and all but I was trying to check things out before installing them.... how does the current flow on this thing?
On the other panels it seems that the red + not attached to the circuit board adds current to the circuit board ?? does that make sense to anyone ?:laughing5:

 

[Coronet 500]

Yes makes sense, in a DC electrical system it flows from positive to negative. So if you have a device that is connected to the negative the + would be "adding" current to the device. Does that make sense to you? If you have any other electrical questions ask away and don't worry about terminology, we'll figure it out together.

 

[99ss]

yeah it looks like the whole frame of the dash board is the ground.. but looking over the painless instructions it looks like I allevaiate the circuit board and tie to each sensor instead of using the pins on the circuit board or maybe I can still use the circuit board... dont I need the voltage regulator or maybe painless takes care of that.. not sure..LOL need to read more I guess and stop just looking at diagrams...hahahaha


how do I check to see of the gages work? I put my small ohm meter on them check continuity basicaly and they did not show any loss but its a 9v battery...LOL the needles didnt move but it looks like the regulator has a 5v side to the gages so should that have moved the needles then with my $30 ohm meter?

 

[Coronet 500]

When on ohms some current does pass through what your testing, but only enough to come back to the meter and do it's job and show you some value or O.L. open line, if it has a digital display. If it is analog the needle will move or not. Be very careful with putting any current to an electronic device, if it's too much they could easily be damaged.I would read and most of your question might be answered. Many circuit boards have voltage reduction components soldered into them for each individual component, bypassing any of these could be trouble.

 

[99ss]

found a schematic finally... its from a charger.. could not find a GTX wiring diagram for the rallye dash.. also read over the painless instructions and it just says to run a jumper t0 the + side of the gages from the B+ wire of their harness... but I cleaned up the board and poked it a bit and I can use the pins as they were intended from Plymouth... the frame of the cluster is the ground

 

[Meep-Meep]

Yes makes sense, in a DC electrical system it flows from positive to negative. So if you have a device that is connected to the negative the + would be "adding" current to the device. Does that make sense to you? If you have any other electrical questions ask away and don't worry about terminology, we'll figure it out together.

Technically speaking electrons flow from negative to positive.

 

[Coronet 500]

Thanks Meep, just trying to stay simple. Didn't want to get into electron theory.

 

[RGAZ]

For reference here are some facts. These are general in nature and not Mopar specific.

Current runs in a "circle" hence the origin of the word "circuit". That being said, the dash circuit board gets power through the "+" terminal and returns power to the battery/alt through the frame of the car. The frame is "grounded" and the metal of the frame is used to conduct current back to the battery/alt. This saves weight and wiring, so only 1 wire is run from the fuse box.

For testing a gauge cluster, you are going to do one of two things: Continuity/Ohm check and voltage check.

A continuity check is when the circuit youa re checking is closed and there is a load or a short conntection. This is tested using a meter set to the Ohm or resistance setting. It will read the "load" across any two points you touch. the meter is applying a small voltage and measuring the current it draws to get a resistance using Ohm's law. Example: You want to check that the lightbulbs work through the connector on the back of the cluster. Connect the black lead from your meter to the ground terminal on the cluster. then probe the cluster pins for the light with the red and look for a measurement. A measurement of "0" or "OL" is an open circuit and a resistenace of 1kohm or so is a load.

Voltage check is when you are ready to apply voltage to the cluster and want to ensure it has power where needed. This is with the meter set to 20VDC or less. it measures the vokltage across two points by putting a larger resistance across the leads and measuring the current across it. This can get tricky if done wrong, but apply a fused 12 VDC to the + pin and the - to the return. I recommend using two 9-volt batteries (18V) in series so the avaialble short circuit current is low. Now put the black lead on the - terminal and probe the red lead around where you think 12 VDC should be. Compare it to the voltage across the battery. Some things may light up but it will kill the 9v's pretty quick. If you want you can use a couple lantern batteries for more check time.

Some areas to be careful around: gas gauge is a milliamp sigal reader, you can actually fry this one if you apply voltage to the wrong terminal. Some tachometers have issues with non-pulsed inputs and they may have issues.