I'm confused with the electrical issue I have on my car.
This is a situation:
1 - originally, the gas strut (hatch) is "wired" and acts as a light switch: when the hatch is closed, the strut is compressed, the circuit is open - no lights.
2 - when the hatch is open, the gas strut is extended and the contact is made to complete the circuit - the light is on.
3 - I had to remove this strut, so I needed to find another way to trigger the light.
4 - I ran a magnetic reed switch NO (normally open) when the magnet is next to it.
5 - the magnet moves and the reed switch closes the circuit - the light is on.
Simple in theory, but... This reed switch gets stuck after it's on for more than a few seconds. I assume that it "burns" and its contacts "weld" together. This reed switch is rated 0.5A 12VDC.
So, I added a relay, 12VDC, 1A, so the reed switch activates the elec. magnetic coil in relay and the relay completes the circuit, carrying more amperage.
I bench-tested this set up using scooter's 12V battery, relay, reed switch, light and wires... all works well - as intended.
When I installed this set up on the car WITH REED SWITCH POWERED SEPARATELY FROM CAR'S WIRING (USING SCOOTER'S BATTERY), the light tuns on. All works as intended.
BUT... when I power the reed switch from the car's circuit, shared by the relay switch and the light, the relay starts to buzz or chatter. Adding a 470mF capacitor in parallel with relay coil terminals "slows" the rate of chattering. 2 capacitors in parallel slow it even more. I thought that reed switch doesn't pass enough current (amps) to keep the relay's coils "closed".
then... I tried to use a different relay, about 0.2A 12VDC - same problem.
What am I doing wrong?
I tried different resistors, all they do is dim the light, but chattering remains.
What do I need to do to fix this problem? and how?

 

Need to see how you wired this relay and reed switch configuration using only the car battery.
Schematic please.

 

From your description it appears you have the relay coil or reed switch wired through the relay contacts.

 

This is a crude schematics. The "block" with a question mark in it designates other wiring, door switches and dome lights, that must be in that circuit. The same layout without "?" block works fine on the bench.

 

sghioto, the reed switch triggers the relay's coil, and the relay completes circuit to light up the bulb.

 

You have the relay contact shorting out the relay coil and reed switch when activated is the problem.
Connect the top side of the relay coil to +12 volts only.

 

Like this:

 

Hm.. that would mean that I have to run a new wire to, let's say, a fuse "+" (within dome lights circuit).
Is there a way to "restrict the flow" and prevent interference between the load and coil sides of the relay? Diode? The reason I ask is that I'd like to avoid more wires in the car. I'm not an electrician and don't know much about it, so, forgive me, if my questions "sound' stupid. What do you think?

 

No way that would work.
Got to have 12 volts for the relay coil.
That's why it worked with that separate scooter battery.

 

So, why did this set-up worked on my bench with single power source? This bench set-up is the same, except that "mystery" box with "extra components"?

 

Draw up how you wired it on the bench setup.

 

This way:

 

Here's the correct schematic.

The flyback diode is required to prevent reed switch damage by inductive kickback from the relay coil.


Nandu.

 

Exactly, one side of the relay and the lamp are connected to 12 volts as I posted earlier.
In the car you are trying to power the relay through the lamp which won't work as you know.

 

Here's the correct schematic.

The flyback diode is required to prevent inductive kickback from the relay coil causing damage to the reed switch.

View attachment 344801
Nandu.

Not wired correctly,
One side of the lamp is 12 volts.

 

Nandu, from your schematic I understood that I placed the reed switch "from neg. side", yours is "on pos. side". I can change "the sequence" no problem. So, what is this diode? What are its specs?

 

Nandu, from your schematic I understood that I placed the reed switch "from neg. side", yours is "on pos. side". I can change "the sequence" no problem. So, what is this diode? What are its specs?

Don't need to change the switch orientation.
Talk about the diode later.

 

A 1N4007 diode should suffice.

 

wwdwgs, do you understand what I said in post #14?

 

do you understand what I said in post #14

not really.