pretty much the circuit less drew here:
https://www.electro-tech-online.com...arm-system-does-not-work.147384/#post-1254145 except make the Normally Closed positions the lower ones.
If you follow the re-configured circuit, the both sides of the motor will be grounded at rest. Activating one relay will unground one side and apply 12V. Activating the other will unground the other side and apply 12 V. If you activated both relays the motor would have 12V on each side. Thus, the directions change and the motor get's braked on turn-off.
A 1n4002 diode should be across the coil. This helps reduce turn off spikes. The band of the diode should face the 12 V side.
The BOSH style automotive relays will work. You may be able to solder the diodes at the coil.
The bigger problem is finding the room to mount the relays. As I said before, the sockets help for a number of reasons.
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What you can check with your DVM is place one probe on 12 V somewhere and the other probe on the orange/white and see if you get a blip on unlock. Do the same for orange and see if you get a blip on lock.
A chinese source:
https://www.banggood.com/12V-12-Vol...with-Socket-30-amp-40-amp-Relay-p-931331.html
If you want a really nice professional installation, use these
https://uk.rs-online.com/web/p/terminal-strips/7033833/ and wire ferrules
https://uk.rs-online.com/web/c/conn...p-bootlace-ferrules/?searchTerm=wire+ferrules.
You can cut the strip to length. In the US, I can buy the ferrules in any quantity. The strip does not appear to have "wire protectors", so the ferrules are necessary for stranded wire.
So, even though the relay is cheap, you can end up with other issues. Wire by the foot in different colors. A crimping tool. Crimped connectors (often available in boxes of 100) Wire can sometimes be had in an automotive store as well as the fast-on connectors. They come in different sizes and for different wire gauges too. You may need clips for routing the wire too or even tape. Tape I use for automotive work is $40.00 USD per roll. It's called self-fusing silicone electrical tape. You might need paint to tough up drilled holes.
reselectronics and farnell are to major distributers on your side of the pond.
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A couple of projects at home were mechanical in nature: One was a stop for a vertical blind. I had to measure (I have a digital caliper) Turned out it was close to 7.5 mm. I bought a 0.250" Delrin 2 piece collar and a 7 mm drill and 7.5 mm reamer. You need a vise and a drill (have). I also needed 4 sacrificial Nylon washers so I could drill the hole. I would also need a hex key wrench (have).