The first item you posted is listed for "vehicles with central locking system", which I take to mean is systems with remote key fobs. With those, there is no one to press a physical switch inside the vehicle, so there has to be a computer module with a receiver, that runs a pair of relays. Door switches to work with these systems have only three wires; a 12-volt feed, one to run the "lock" relay, and one to run the "unlock" relay.
I put together a description of how the older lock systems work. It shows how the door switches are both in the circuit when either one is pressed. This description is rather cumbersome, and it makes more sense when it's explained with an overhead projector, but see if you can get something useful out of it.
Power Lock Operation
The first diagram is for the complete circuit in an '88 Grand Caravan except for the lock motor for the sliding door. Circuits X34 14PK and X33 14OR at the center, right side go to that lock, and those two wires would be used for both rear lock motors on four-door cars or trucks. This circuit is typical for most car brands and models up to the mid '90s.
Look first at the top of the second diagram. That is just one switch expanded for clarity. The switch has two independent double-throw switches built in. The green arrow is pointing to one of the movable contacts. There's no dashed line between the two movable contacts. That shows the two are not ganged together, so activating one leaves the other one alone in the released position.
Both switches are released. In the lower drawing, the blue line shows those contacts, and the red line shows that current can flow through them. The same is true for the lower contact, and current can flow through that pair of contacts too.
On top of the third drawing, the pink and orange lines show the two circuits and their four terminals. While the ground connection isn't shown on the first diagram, both of these circuits go to ground, through the two circuits in the other switch. Before we get to that, the important point is all four of those terminals must read continuity to ground. Note there's five wires connected to the switch. If you start out with a test light, you'll find one terminal has 12 volts on it. Regardless of how the terminals are arranged, once you identify the 12-volt feed wire, it's easy to know which other four wires must read continuity to ground.
At the bottom of the third diagram, the upper switch has been activated, as shown by the pink lines. The red line shows the path current takes, and note that it comes in on that fifth terminal.
Getting back to the released switch, in the fourth diagram, one half of the motor's circuit is shown with the orange lines. Start at the motor at the top left, then follow the path through the connector, down through splice X33, through the bottom half of the right door lock switch, then continues up through the bottom half of the left door switch. Once the path exits at the lower right terminal, it's a constant ground circuit as noted by the black lines. This shows that when both switches are released, the orange wire at the motor will read continuity to ground.
The other half of the circuit works the same way. In the fifth diagram, it is outlined with the pink lines. The point is everything has continuity to ground. A quick test is to unplug the lock motor, then measure from each wire in that plug, to ground, and you should find very low resistance. If you find an open circuit, there is a bad contact in one of the switches or a break in one of the connecting wires. Between these two circuits, there are a total of four contacts in use when both switches are released. This is why a defective switch can be the one that seems to operate the locks properly.
To be valid, those resistance tests must be done with the lock motor unplugged, otherwise, if there's a break in one circuit, the ohm meter will still read a real low value through the motor, then through the other circuit.
In the sixth diagram, nothing has changed in the pink circuit, so the top left lock motor's lower terminal is still grounded. The driver's switch has been pressed to the "Lock" position, as indicated by the green arrow. The orange contact has moved away from the ground contact at the lower right corner of the switch, them made the contact to the red 12-volt circuit. That places 12 volts on the entire orange circuit, including the top terminal on the lock motor. Once you follow the 12 volts through splice X33, it also shows up at all the other lock motors.
12 volts can also be placed on the orange circuit by the passenger's switch shown at the bottom of the diagram. That switch has 12 volts on its center terminal just like on the driver's switch.
The same type of operation occurs to unlock the doors. In this case, the orange contact would be released, and the pink contact at the top of the switch would break its connection to ground, then move to the 12-volt contact. That puts 12 volts on the lock motor's pink terminal while leaving the orange terminal grounded. The polarity of the voltage applied to the motor is reversed, so the motor runs the other way.
The reason this circuit can appear complicated is by designing it this way, if the driver and passenger each press their lock switch at the same time, nothing will be damaged. If they both press "lock", they'll both put 12 volts on the orange circuit, and the doors will lock. If one person presses "Lock" and the other person presses "Unlock", 12 volts will be placed on both the orange and pink circuits, so the difference between them is 0 volts, and the lock motors will do nothing. Also, to do that, each switch has first broken one of the ground paths for those two circuits, so there is nothing to short the 12 volts to ground.
Even if a short were to occur in the system, it is protected by an auto-resetting thermal circuit breaker. Power locks and power windows are considered safety systems, so they're protected by circuit breakers instead of fuses. A blown fuse is permanent until you can stop to replace it. The thinking is an intermittent short can render the system dead, but if that short goes away, such as right after the impact of a crash, it's possible for the circuit to work again once the circuit breaker resets. That can take as little as five to ten seconds.
To address your question about which switches to order, you can see those in these diagrams have five wires going to them, but that can be misleading. In the left door switch at the top of the diagram, the top left and lower right terminals both go to ground. They're tied together outside the switch, but they could be tied together inside the switch, leaving one less terminal to connect a wire to. They connected them externally because they can't be connected that way internally for the passenger's switch at the bottom of the diagram. Doing it this way means both switches can be of the same design and they'll work in either location. To leave off that one terminal would save very little cost but it would require building and stocking two different part numbers.
The next issue is the switching of polarity is done here by pressing a switch. In a lot of newer models, GMs in particular, the engineers can't seem to satisfy themselves with how complicated they can make a simple, reliable circuit. One of those complications is to do that switching with a pair of relays. The relay's contacts break a ground circuit first, then they apply the 12 volts to that circuit, just like the switches did. The relays are activated with a door switch of simpler design. All those need are the terminals for the 12-volt feed, a "lock" circuit, and an "unlock" circuit. Three wires to run a pair of relays.
You have to know how the aftermarket people are doing their switching to know which type of switch to order.
Be aware the circuit for the '88 Grand Caravan can not work with any type of remote keyless lock system. Those systems use a relay to put 12 volts on one of the lock motor circuits, but when the door switches are released, they're keeping those circuits grounded. Trying to put 12 volts on a circuit that's grounded will cause a short.
If it will help, I drew up diagrams to show how those switches I found on eBay would work. The terminals look like any standard double-pole, double-throw switch, but these are different. With a standard switch, you would find terminal 1 connected to terminal 2 at the same time as terminal 4 is connected to terminal 5, as in Figure 2. Flipping the switch connects terminals 2 and 3 together and terminals 5 and 6 together, as in Figure 3. You only have a choice of those two positions.
The switch you need has three positions with the center-off spring-loaded to stay in that position. When not being pressed, there's no connections between any terminals. When you do press it one way, the connections are as shown in Figure 2. 12 volts is applied to the pink wire on the lock motor and ground is connected to the orange wire. When the switch is pressed the other way, as in Figure 3, the pink wire is grounded and 12 volts is applied to the orange wire. The polarity is reversed at the lock motor.
The important point is in the original Caravan system, the switches keep both motor circuits grounded when they're released. When a switch is pressed, it removes one of the ground connections and puts 12 volts there.
In the system using the switch in Figure 1, both circuits are open when the switches are released. When one of them is pressed, ground and 12 volts are switched on to the two circuits at the same time. Any number of switches can be added to the system, and one of them could be a pair of relays. Each relay can have two sets of contacts, one to switch on the ground, and one to switch on the 12 volts. Those relays can be operated by a remote key fob and receiver module. In this circuit, since no motor circuits are kept grounded, there will be no short to ground when one of the relays puts 12 volts on one of the motor circuits.
Images (Click to enlarge)
Monday, December 16th, 2019 AT 3:38 PM