power distribution

The fuse panel with ground bus isn't needed. The panel with the cover over the fuses isn't needed either. The panel is inside the box, correct? Just chain the relay coil negatives from one to another. Don't rely on the box to provide a ground. Six relay coils will be less than 1A with all operating. 20 gauge wire would be fine in this application. Suppression diodes across the relay coils might not be a bad idea. The terminal strip with the quick connect terminals shown earlier will help simplify the wiring, unless soldering was desired. Heyco, among others, have grommets that also work as a strain relief. Nothing wrong with overbuilding!

Nice! Mark - why might suppression diodes be a good idea in this application? Overbuilding is always my preference! And future-proofing, too!

The diodes, when connected properly to the relay coils, will prevent damage to the circuitry controlling them. They will also help with interference caused when the relays are operated...turn off clicks and pops.

So - wired in series between the trigger source and the trigger terminal of the relay then? How does one calculate the optimal value of the diode, please? (I am quite out of my element in this aspect of the discussion!)

It would be a 1N400* series diode...1N4004 is fine. Connect the cathode (banded) side of the diode to the positive side of the coil, anode to the negative. On a bosch type relay, terminal 86 is typically the positive, terminal 85 the negative. More info can be seen here: http://electronicsclub.info/diodes.htm

Understood - many thanks!

Well - I'm on my way. I couldn't find a reasonably-priced die-cast box (the smallest that would fit the four relays and the fuse block was just under C$17 + 13% tax)and was fairly thick aluminum, so I picked up two slightly different sized plastic boxes. One of those will do the trick I think. And I actually found a SPST relay with a diode wired inside...which I thought was kinda cool. And it was fairly inexpensive too; $5.65 + tax, but when I got it home and had a closer look I realized it had no mounting rail/tab...nor does it have a 15mm slot. So if I'm gonna use it I'll have to hot-glue it into the box, which seems less than ideal. Since I also bought a 10-pak of diodes...I think I'll return the protected relay and pick up another SPDT with a plastic mounting tab. That way all four relays will be the same. I will probably still squirt a dab of hot glue beneath each one when I install it...but I'll also drill a small hole through the project box and run a short bolt thru to tie the relays in position. And I had intended to utilize the pre-wired sockets with pigtails [again] but I decided not to because: a) the pigtails seem to be incorrectly configured; the heavier-gauge wire is on the coil terminals instead of the switched terminals b) the wire that connects to the #30 terminal is black and the 87 is red, which strikes me as being bass-ackwards, and that'll bug me to no end c) the interlocking style of socket is pretty bulky compared to making my own direct-to-spade wire harnesses, which matters because I'm trying to keep the box reasonably small I realize that whoever may be reading this probably couldn't care two hoots for how I'm doing, and I completely understand that. I'm just thinking out loud in the hope that if I sound like I'm going off the rails...somebody will pipe up!

Well the heavier gauge on the coil wiring is strange. But the terminals in the sockets are usually easily removed with the proper tool...think jewelers screwdriver as a substitute. Then all wires could be removed and repositioned. The sockets being bulky can be an advantage if they link together and also have mounting tabs. This would allow the relays to be mounted securely. Place the top edge of the relays against the case to lock them in position, mark the mounting holes, drill and fasten.

Well...I'll see when I pick up the four-fuse terminal block on Monday afternoon. Once I have it in my hand I can lay it out adjacent to the four relays and determine which of my two boxes is the right choice...and then I will decide about the sockets. In fact, none of the three that I currently own have mounting tabs; just the interlocking slides & grooves. But three out of four relays have mounting tabs, so I will stick to small nuts 'n' bolts...a dab of hot glue...and individual wires. I am really stoked about this little project! I look forward to laying out the wires and securing it all inside the little box. The majority of the processes are not new to me, but the idea of the containment enclosure definitely is! I have always tried to do jobs like under-hood wiring neatly & carefully, and for the most part I think I do alright. But this whole project box scenario represents one of those Aha! moments in ones life where you find yourself branching out along a new & interesting line of thinking. ANd I am VERY pleased & grateful that you have shown me this fresh challenge, Mark. Thank you!

Okay! I think I'm on the right track here. Absolutely everything I know about diodes has been uploaded into my brain in the last 18 hours or so, so bear with me! I have begun the wiring by inserting the diodes into the circuit in parallel across the coil terminals as shown. The actual science is a bit fuzzy, but I'm trying to grasp it. As I see it, the diodes do not (cannot) block any electricity when the coil is energized because: a) the electricity is flowing through the coil from + to - and effectively "bypassing" the diode b) there is not (or should not) be any energy flowing "backwards" from the NEG side of the relay anyway But -- at the instant the coil is DE-energized -- there is residual energy in the coil that could theoretically cause problems. And the sudden discharge/collapse/burst of this residual energy is blocked/dissipated by the diode so that it cannot travel...to...where, exactly? When the coil is DE-energized, the residual energy in the coil is expected to "loop" "back" through the diode...and thence deplete itself by running in a closed loop until dissipated. And this is intended to "shield" the upstream components (in my case, a wireless switch) from that trace of reversing energy. However... The trigger wire remains attached to the POS side of the relay all the time. And if the diode is wired in parallel across the coil terminals...it too is therefore attached to the trigger wire all the time. So... Assuming that the flow of electricity "exits" the coil at the NEG side when the coil is energized, when the coil is DE-energized, does the residual energy in the coil continue to flow in that same direction? If yes, then most of it will go to GROUND, and any tiny bit that tries to sneak back through the diode will be blocked...and therefore NOT reach the wireless switch. :) But is it possible for it to "leak" backwards? (reverse direction?) If so, then it will encounter the K end of the diode, which will allow it to pass through the diode and re-enter at the NEG end. Which is okay. But it will also encounter the trigger wire. So what's stopping it from travelling upstream back to the wireless switch?