As for whether you need two actuators or not - I don't know. That would depend on your vehicle's trunk latching mechanism.

There has been some question about the WOLF. Does the "Momentary Ground" provide power when it's not grounded? My guess is that it probably doesn't. Even if it did it's not likely going to be enough current to actuate the actuator. Since it provides a momentary ground, assumably only during the time you want the trunk to pop open, I would assume that it is necessary that the relay has a constant source of voltage. The drawing you posted shows one side of the coil connected to ground. When the WOLF goes to ground you now have your relay thoroughly grounded on both inputs. In that instant of time the relay will do nothing. And if your WOLF DOES provide power at all other times, your relay would be active at all times except for when you want to pop the trunk. The relay will warm, and eventually may get hot enough to burn something. So I'd say your diagram is wrong. On pin 85 you should have 12V continuous source, not ground. When the WOLF commands the actuator to pop the trunk it will give you a momentary ground and the relay will then trigger the actuator. THAT is when you want the trunk to pop open; when the WOLF provides the momentary ground. To depend on a continuous source of current (not voltage) to hold the trunk closed and locked, when that current fails the trunk will pop open at will. Not at a time you wish.

Thank You,
I asked ChatGPT to improve his answer and this is the new one, just like your wiring diagram. The WOLF central locking is the best brand in Egypt, So I think it's protected enough, but I think adding some diodes won't hurt. which diode is most important than the other? the diode between 85 and 86 or the other one on the solenoid?

1. Pin 85 (Relay Coil): Connect this to a 12V positive source (e.g., ignition-switched or battery power through a fuse). This powers the relay coil.
2. Pin 86 (Relay Coil Ground): Connect this to the grey wire from the Wolf central locking system (momentary ground output for the trunk). This will activate the relay when the trunk button is pressed.
3. Pin 30 (Power Input): Connect this to a 12V fused power source (e.g., directly from the battery). This supplies the power that will drive the solenoid.
4. Pin 87 (Power Output): Connect this to the positive terminal of the solenoid. This pin sends the power to the solenoid when the relay is triggered.
5. Ground (Solenoid): Connect the negative terminal of the solenoid to a good ground point on the car’s chassis (bare metal).

Key Considerations:

• Fuses: Add a fuse to the 12V power supply (Pin 30). A 15A fuse should be sufficient for most trunk solenoids, but check your solenoid's specifications to be sure.
• Wire Gauge: Use a wire gauge that can handle the current. For most automotive relays and solenoids, 16 AWG should work well.
• Relay Rating: Ensure the relay you are using is rated for at least 30A.

 

One thing is rather obvious about automotive applications is the very long life of contacts

Define "long life"? MTBF is a good metric within specific test conditions, usually in context of "cycles". It's also relative to relay size. I am not sure if relays are linear in that sense, if I can make a relay 2x bigger does that get me 2x the MTBF of the smaller relay, or maybe I can get 2.5x the MTBF? Certainly in general, as new materials come to market we get better products.

 

The "Long Life" of an automotive relay for me is that the relay still works when the rest if the car fails. Typically a bit over ten years and 160K miles. In an industrial machine, if the machine still runs up to the day it is obsolete and discarded.

 

The "Long Life" of an automotive relay for me is that the relay still works when the rest if the car fails. Typically a bit over ten years and 160K miles. In an industrial machine, if the machine still runs up to the day it is obsolete and discarded.

Years and miles are related to cycles and ckt in what ways? It must be related, otherwise the MTBF metric becomes a bit meaningless.

10yr 160kmi is a number when vehicle fails? Maybe for some makes/models. I have a vehicle that is still 100% mechanically, 20yrs old @ 265kmi. I had to replace my fuel pump relay twice, seems like fatigue had set in, one on contacts and the other failed throw.

But I do agree, if we get 10yrs out of the relay then it's probably ok to say it is "long life", relatively speaking.

All that said, solid state switch is better.

 

Consider the relay of the direction indicator (these days this relay has been replaced by electronics and LEDs in place of bulbs): have you ever experienced a failing blinker relay? And these have I-don't-know-how-many switching cycles over time. (And also quite harsh operating conditions as the current during switch-on is quite high (as the cold filament's resistance is way lower than when hot).

 

My cousin has a tube of toothpaste. Had it over five years now. Says it will last him another 20 years. He never uses it.

Airplanes have timers on their engines. After so many hours FAA (United States) mandates an engine rebuild or overhaul. If it sits in the hanger for years you could say it lasted a long time MTBF. But they're called "Hanger Queens". Pilots don't like to rent those because they're not well exercised and it's believed they are more prone to failure. An engine gets hot and moisture in the engine block evaporates. If the engine never runs then corrosion sets in and the engine becomes unreliable from lack of use.

So there's both sides to every Crepe. Well, not so in my mother's case; she made Crepes so thin they only had one side. Flip it over and it was gone forever.

 

Consider the relay of the direction indicator (these days this relay has been replaced by electronics and LEDs in place of bulbs): have you ever experienced a failing blinker relay? And these have I-don't-know-how-many switching cycles over time. (And also quite harsh operating conditions as the current during switch-on is quite high (as the cold filament's resistance is way lower than when hot).

It's interesting. Car makers are still pumping out vehicles 1,000 per day, still using old mechanical relays. For some things you can put a "ssr" into the same relay package, yet they don't do it. In some cases xPyT relays are easier when needing to switch multiple ckts different ways using just one control signal, which is often silicon that controls the relay coil.

 

When the failure mode of an item is well known and well understood it becomes possible to produce versions that last a very many cycles. The clutch control relay on an automotive AC system is a good example. On the high end AC systems with a evaporator pressure sensor it will cycle a whole lot and yet not fail. In the TS request we are given neither current nor cycle rate nor how critical the function is. So do we suggest the $2 relay used for a cheap appliance or the $32 relay used in a respirator motor control circuit??

 

Use a standard automotive 4-pin relay(pins 85, 86, 87, and 30):

• Pin 85: Connect to ground (chassis).
• Pin 86: Connect to the grey wire from the Wolf system (the momentary ground wire).
• Pin 87: Connect to the positive wire of the solenoid.
• Pin 30: Connect to a fused 12V power source (e.g., directly from the car battery or another suitable 12V circuit in the trunk).

For the number of life cycles a trunk lid solenoid is going to be operated I don't think we're going to need to over-engineer a design. As already noted, the drawing above has both 85 and 86 grounded. ChatGPT has it wrong again. Since the grey wire is a momentary ground and is wired (in this case) to pin 86 then pin 85 must be connected to a constant power source (through a fuse obviously). With pin 85 to power and a diode as is shown in post #12 is recommended.

Beyond deciding if a relay is good enough or not - in this case, the automotive relay you can get off the shelf at an auto parts store is going to be 100% sufficient for the purpose for which it is going to operate within.