Here is another dumby question. My Specialty. Where can I get high, auto quality wire, and what size should I be ordering, or purchasing?

I am going to move the ECU into the passenger compartment. This will involve splicing about 3 feet of wire into each wire in the ECU harness. I don;t see this as a hard job, just an organizational challenge.

The plan is to cut each wire, one at a time, and splice an extra length into it, which will then be folded over temporarily untill all are spliced, at which time I can unplug the ECU, move it into the pass compartment under the dash, push the new extended harness plugs through the firewall, and plug everything back in. Cutting only one wire at a time will allow me to keep the car drivable, and thereby check the correctness of my work one wire at at time.

Is the wire availiable at local stores good enough? It certainly does not look as good as what you take out of an OEM harness when you clip it. And, I am unsure of how to size wire. How do I tell what size is in the harness now? Different thickness insulations certainly can make the same size wire look different, and different sizes look the same. Also, is there a heat rating on wire? Is the hook up wire sold a Radio Shack good enough to withstand underhood temperatures? Of course every wire in the harness is essentially a unique color or combination. I don't think I can duplicate that, but maybe I can keep the base color the same. That's not too big a deal since the same color will be going in, and out of the harness at each end. Mainly, I think the most important thing is to have it flexible, and heat resistant.

These are low current carrying wires. Any rules of thumb? Thanks for the advice. I wish I have been more help to others lately.

Sam

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I'd usually use 20-18 gauge wire on low current ones and maybe 14 gauge for high current (like injectors). You'll want wire specifically made for automotive underhood use like TXL or GXL. There's a good explanation of insulation types here. We've got a couple bundles of wire in assorted colors at work, although the labeling is not going to match an Accel harness and the color coding is probably going to be a bit different too.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Matt, can you sell me a bundle of wire? How do I do that? Give you a call? I'm happy to take what I can get on colors.

Sam

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I have ordered here and found good quality, reasonable prices and fast service. They have automotive rated wire, weather-pack connectors, tools, wiring looms ....

http://www.waytekwire.com/

Really depends on how high you mean when you say "high quality", how much you need, how many different colours you need, how quickly you need it. For most automotive applications, a locally-purchased reliable brand of PVC-insulated stranded copper wire is more than adequate. Good brands include Belden (NAPA), PowerPath, and Carol. Try to go by country of origin. If for whatever reason you feel you need truly extreme heat- and chemical-resistance, then you want crosslinked insulation. Look for a wire designated with "XL" ("XL-DUR" from NAPA-Belden, GXL, TXL, SXL, etc.). Usually this will need to be specially ordered, and fewer colours are available. Other premium grades of wire include "Marine" wire (which is available in an especially large range of colours, as it seems) and If you can wait, Waytek's one of several good mail-order sources.

I have to disagree with Matt C on one technical point: Never use 20ga wire in a car. OEMs use it to save money, and sometimes it's electrically adequate, but its mechanical strength is poor. Better to use nothing smaller than 18ga simply to assure a robust job that won't fail mechanically. Other than that, when choosing wire gauge, make sure to use sound numbers for your calculations.

Always use stranded wire, never solid wire, in automotive applications.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If Matt can't help, it may be hard to find short lengths of something that thin at a retail store.

If you only want to extend in middle of harness you probably don't care about colors. Maybe you can just get a roll or two of the same color? Also, are any of the wires in the harness shielded or not?

Never use the same colour of wire to extend or repair adjacent wires originally of different colours. If you do this, you will be very, very sorry someday when you have to diagnose and repair faults in that wiring. It is just plain impossible to keep track of which blue wire goes where when there are a bunch of identical blue wires going to about the same place. Put in the effort and time to find and get multiple colours of wire, or at the (very) least clearly and indelibly tag your same-colour wires with the parent wires' original colours.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan, Do you think your rule about no wire as small as 20 applies when there are going to be over 20 wires in a bundle inside a harness. It seems as if having them all together might give them the strength you are looking for in size 18. Also, the smaller wire is going to produce a neater, more compact harness, which is more flixible. I will need to put this cable of individual leads through a gromet in the fire wall. I wonder what size the wires are in the Accel harness. It seems as if the insulation on the Accel wires is expecially tough. It was harder to strip than supply house wire. It seemd harder, and more flixible all at the same time.

Matt, I looked at your web site. That kit looks terrific, but might be overkill in this instance. If I ordered your kit, I mgiht be tempted to start over, and completely rewire the harness. Since everything is working now, I am a little concerned about fouling something up by doing it over completely. I was really impressed with the wide array of products you guys offer. It opened my mind to some things I did not know even existed, such as the boost control interface for the GM boost control There is alot to learn yet. I am reading Corky Bell's Mazximum boost, and have not yet seen a reference to computer controlled boost control. I will look for that in the book, and see if he mentions it. Do you have a link I could go to to find out more about this? Of course the Accel likely does not support this, but it would be nice to add that to my understanding of this stuff.

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The boost control solenoid? It's a cousin to the bleed on a wastegate, only the computer can change how far the bleed opens.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

I spliced in the 3' extensions into all the sensor wires, and bundled them up. It is tied up out of the way awaiting me to do the same to the rest of the ECU wiring. I started the engine and monitored all the sensor readings, and I didn't goof anything up. When the rest of the wiring is done the same way, I will move the ECU into the cabin under the dash. The remaining wires are injectors, the TPS and ignition wires. I would like to organize them better than they are now. All are kind of bundled together, and it seems maybe it would be a good idea to keep these in seperate bundles.

The ignition wires include some shielded cable. I am unsure of how to go about dealing with this. Is there a shield I can wrap around my extension. Would simply wrapping some aluminum foil around the extension help at all? I wonder where I can get shielded cable. I think the outside shield is grounded.

Another decision to make is whether to keep the automatic igntion retard wiring avialable. Accel says it is impossible to wire this feature and a knock gauge too. It seems the knock gauge is far more important for tuning than the knock retard feature. I guess the knowck retard feature would allow me to run regular gas after I get it tuned up. I'm not sure how I feel about that. I also have the NOS wires wrapped up and stored beside the ECU. I could just clip these off, and eliminate some more clutter. I think I will post a seperate question about that.

Sam

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A couple factory harnesses almost use something like tinfoil for shielding, so if you don't have any automotive grade coax wire I could see that working. Just don't let the shield ground to the body of the car.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Correct my thinking here. I thought the shield was grounded. I thought that was how it worked, by grounding out any interference. I am an admitted electronics dummy here, so don't worry about offending my sensabilities here. If that were the case I would never learn anything.

Sam

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It is grounded, but only at one end. It's possible for other spots on the chassis to be at slightly different voltages, and that causes current to flow through ground wires. This can drive your sensors bonkers.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Here are some wiring suggestions. On the shield splice, it may be best to use copper tape. Run the tape long ways, solder the shield wires at each end then solder at a few places along the seam. A flexible heat shrink or loom may be used for the outer insulation. There are also copper bismuth foils and screens used EMI suppression work. Some have conductive adhesive that may work too without the solder.

In routing the wiring it is best to separate the signal and sensor wiring on different routes from the power wiring. The power wiring includes coil drive and injector wiring, and supply to ECU and fuel pump.

On wire size - 16 ga. stranded automotive wire is a good minimum. Use 12 ga. or 10 ga. for high current and low voltage drop for fuel pump, ignition coil or supply to ECU.

Avoid wiring loops. Think how a table lamp is wired. The supply and return (H and N) are close together. There is a canceling effect because of this geometry. Current directions are opposite, external signals are nulled. In instrumentation systems, twisted pairs are used to take it a step further. Coax is one step further. The loop I mentioned to avoid is when a supply and return wiring are far apart. An example is supply routed on one fender to a sensor and the return routed on the other fender. Other wiring inside the loop may radiate energy that is picked up by the loop, things like spark plug ignitions.

Good wiring practices and proper routing are essential for proper noise control.

Thanks for the tips Kit. I will keep them in mind. In the original harness, the power circuits were in one leg of the harness, and the ignition harness ran seperately. I can see the logic for that.

Sam

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