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Starting thread to share various DIY automotive electrical tools, tips, techniques and special parts that help ensure a good electrical addition. Please feel free to share your own and add on to the thread.

Some of this will be basic stuff to those with experience but may help those wanting to try and do some electrical additions themselves as even with very basic knowledge and a few tools you can do much better work than your local automotive shop/speaker shop/Best Buy.

Tools:

Soldering iron and solder. The backbone of all good automotive electrical additions. No need to break the bank here, even a cheap entry level one like this will last years and handle all your wiring harness creation needs:
1_D4C9591 by S L, on Flickr

Wire strippers and clippers. While you can get by with a straight razor blade just fine but a pair of wire strippers can help. Best not get the cheapest one in the store as they can be more frustrating than useful:
1_D4C9586 by S L, on Flickr

Electical tape, solid and liquid. I generally avoid using standard electrical tape in favor of heat-shrink tubing, but liquid electrical tape is useful for sealing taps into other wires ("T-tapping/3-way") and or for anything exposed to the elements/outside the passenger compartment:
1_D4C9592 by S L, on Flickr

A cheap multimeter (not pictured) can come in useful for more advanced electrical projects and diagnosing problems but is not really necessary for your typical electrical accessory addition.
 

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Discussion Starter #2
Special Parts:

Add-A-Circuits. Very useful for utilizing empty fuse slots in the under-dash fuse box. For example adding a dash-cam while keeping the 12V 'cig-lighter' open. Pick up some ATM LP fuses as well as they are the most common fuse on the CR-Z and its a good idea to keep some in the glovebox.
http://www.crzforum.com/forum/do-yourself-articles/5734-tested-interior-fuse-box-18-19-charlie-sheen-winning.html
1_D4C9585 by S L, on Flickr

Pigtail plugs. These can be had many places online and some selection in local auto parts stores. Good for adding something to an existing light plug, for example if you wanted to change your fog lights to something else but have them plug in to the factory harness. They come in nearly every type of common plug style (usually indicated by the type of bulb or original manufacturer of plug-style).
1_D4C9583 by S L, on Flickr

Heat shrink tubing. Far superior to electrical tape (except the liquid variety), easy to use. Apply heat (lighter/heat-gun/stove) and it shrinks. Hardest part about using it is remembering to put them on before you end a harness.
1_D4C9581 by S L, on Flickr

Flex loom. Good for protecting wires and harnesses from abrasion and damage. Also helps give your wiring a professional OEM look. Most common small harness size on a Honda is 1/4".
1_E1C8648 by S L, on Flickr

Harness ties. Regular zip ties work ok, but if you want a really clean OEM look and the best protection these OEM Honda zip ties feature an end that clips in to all the various open holes (both threaded and those without). Click for larger if you can't see the part numbers.
1_E1C8651 by S L, on Flickr

Engine Wire Harness Ties:

http://www.hondapartsunlimited.com/auto-parts/2011/honda/cr-z-hatchback/ex-trim/6-speed-manual-engine/engine-cat/engine-wire-harness-scat

Other Harness Ties/Bands:

http://www.hondapartsunlimited.com/auto-parts/2011/honda/cr-z-hatchback/ex-trim/6-speed-manual-engine/electrical-exhaust-heater-fuel-cat/harness-band-bracket-scat

OEM Honda 10mm (M6) ground bolts. Special bolts designed to get good ground every time. They have thread-tap-style thread-chasing cuts in the bolt. Many of the un-used 10mm holes you may want to use as a ground will have paint in the threads and these clean that out for good metal-to-metal contact. Use with ring terminals.
1_D4C9636 by S L, on Flickr

Ring terminals and quick disconnects. Ring terminals are good for adding ground connections and positive connections off the battery posts. The quick disconnects are good for connecting easily directly to relays.
1_D4C9580 by S L, on Flickr

ATM-LP waterproof inline fuse holder. These can be hard to find so if you need any I have a batch that I had to buy in bulk. Good for adding accessories that will draw off the battery in the engine bay (switched from a relay to avoid drain), especially if you don't want to go through the firewall.
1_D4C9589 by S L, on Flickr

Switches. Obviously when you want to manually control when an accessory is on, less obvious is paying attention to the amperage of the switch and your accessory. Always make sure the switch can handle more than your accessory requires.
1_D4C9588 by S L, on Flickr

Wire, if you don't have any you want to take a quick look at the load of your accessory (in amps or watts, they can be converted to find the other if you don't know it since we know the voltage is 12V) before you spend money.
Amps to watts (W) conversion calculator

You will also want to know the length/distance of wire you will need as it will also affect your wire gauge choice.

Amps and Wire Gauge - 12V Circuit

So distance and amperage will determine what gauge of wire you want to use. You don't want to just get thick wire as a blanket for everything as its a of waste of money and thicker wire is generally more difficult to work with.
1_E1C8652 by S L, on Flickr
 

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Tips/Techniques/Tricks:

Basic soldering. After you clip and strip a wire the copper strands will be straight and want to fray. You want to twist up the ends and then twist the wires together as smooth as possible.
1_D4C9598 by S L, on Flickr
1_D4C9599 by S L, on Flickr

Don't just clump the solder on top of the wires, you want to hold the iron there, feed the solder in and it should flow into and in-between the individual strands of wire. Get all sides around the connection, wait for it to cool and you can smooth out any rough spots with the iron.
1_D4C9603 by S L, on Flickr

Soldering crimped connections can add a lot of strength to a generally weak connection. Even a good solid crimp can be easily pulled apart, the last thing you want is a powered wire coming loose from a crimp and shorting out on something.
1_D4C9607 by S L, on Flickr

Use heat shrink to improve coverage on any open connection. The standard plastic crimp end offers little protection but you can take a tube of heat shrink all the way to the end of the connection.
1_D4C9608 by S L, on Flickr

Tapping into a wire that you don't want to cut. This takes a little patience and finesse but start by taking a straight razor blade perpendicular to the wire and lightly sawing through the insulation. Do this twice the length of an average stripped end, then score that par the length of the wire.
1_D4C9613 by S L, on Flickr

1_D4C9618 by S L, on Flickr

1_D4C9617 by S L, on Flickr

How to wire a relay and why.

So you want to add better horns, or you want to add lights to your rear diffuser to come on with the parking lights and or brake lights. You want to use a relay. Every car can only provide so much energy and each circuit is only designed to provide and handle so much. Adding something to that circuit will over-draw it, result in less than full output and will result in lower switch life and potentially expensive and time consuming OEM wire repair. Save yourself the hassle.

A relay basically tells another device to turn on. It takes a signal/trigger wire from your original device, a fresh 12V source, a ground and provides the output to that new device.

http://www.rattlebars.com/mtz/basicrelay.html <- Great summary of a relay

A standard SPST '4-post' (Single Pole Single Throw) relay.
1_D4C9572 by S L, on Flickr

How to wire it. This is a standardized output. They all use the 30/85/86/87 numbering but always double check on the relay itself. If you get it wrong its not the end of the world your device just won't work until you switch to the right config, which is why I prefer to use the quick disconnects instead of the pre-made relay pigtails.
1_D4C9621 by S L, on Flickr

It looks like a mess there just to show where each connection goes but once you've got it wired you can bring all the wires together and clean it up.
1_D4C9624 by S L, on Flickr
 

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: Post reserved for your future contributions, any special tools you like, parts, tips/techniques/tricks and or examples of work you've done. Anything that can help other members. :

Feel free to add anything you think may help and I'll edit the posts to include it.
 

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Wow! Bump for a great post.

No I just need to re-do my trailer wiring taps on my SUV... not that I used those clip-on taps... At least its a removable harness and I can fix it easily.
 

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Tips/Techniques/Tricks:...
1_D4C9624 by S L, on Flickr
Excellent write-up, Koala. The only extra thing I do when heat shrinking multiple wires, is to slip on an extra large piece over the four wires to later heat shrink it over the end of the flex-loom, and a medium size heat shrink to cover over the individual heat shrink 4-wire group. And you're right, the toughest thing about heat-shrink is that moment when you've already soldiered the wires and find you've forgotten to put that heat shrink on it beforehand. UGH!
 

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......its always worth the extra effort to do it as best as possible as it should last the life of the car just like factory wiring. .....
....which is all done with crimp connections- however, they're done with the proper crimpers which actually fold the tangs amongst the wire strands, not mashed like a spoon into potatoes. If you have the correct tools, solder can be overkill.
 

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Yeah, I've done wiring projects only to realize after completion that something was forgotten or needed to be redone but its always worth the extra effort to do it as best as possible as it should last the life of the car just like factory wiring.
Yea, my trailer harness looks like your "Don't do this ever" example with the tap splices... I at least wrapped it in self-sealing silicone electrical tape.

Basically the Explorer trailer wiring is all the same up to the pigtail to the connector, so I spliced a 4-pinharness and 7-pin harness together so that I had both plugs at the hitch. Works great for not having to have an adapter, but now that I have learned more about this sort of thing, I want to go back and atone for my sins.
 

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Probably not. Koala got some pee on his fur or something, and doesn't come round to see us anymore. The hazard of getting serious in a car forum.
 

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For DIY articles like this and others that have been stickied by the admins, I vote that AutoGuide ponies up- I mean, offers to host and/or subsidize the cost of the Photobucket subscription so we're not losing out on what would otherwise be excellent resources. Just a thought. Hope AG doesn't ban me for that.
 

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For DIY articles like this and others that have been stickied by the admins, I vote that AutoGuide ponies up- I mean, offers to host and/or subsidize the cost of the Photobucket subscription so we're not losing out on what would otherwise be excellent resources. Just a thought. Hope AG doesn't ban me for that.
+1000 on this! This is one thing that absolutely pisses me off about most of the diy here!

Hell, I'd even host them if I HAD the pictures and could edit the posts!!

But really, they should just get us some hosting, or another solution. This info is invaluable!!
 
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