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Replacing wiring

Hey guys, this is sort of a general question about electrical maintenance. I’ve got some wires that are going bad in my 1996 Mercury Mystique 2.0L Zetec automatic (not that that’s too relevant). Anyway, I’ve got some wires with cracked insulation and exposed copper (specifically the ones leading to the ECT sensor and temperature sending unit). I’ve patched them up temporarily with electrical tape, but I’d like to splice in fresh wire. Anyway, I’ve got a few questions about how to go about this:

1: how do I determine the gauge of the wire? I’m tempted to just cut one, strip it, and measure it with a wire gauge tool, splice it temporarily, drive to the store, buy wire, and splice it correctly. Does that seem like an alright course of action?

2: What sort of splice do you guys use? Is one of the two-ended crimp-on splices going to hold up with all the heat right next to the exhaust manifold? I should really own a soldering iron; should I go ahead and buy one for this job?

3: dialectric grease in the crimp or not?

4: how close to the connector at the end of the wire should I put the splice? I’d like to get rid of as much of the old rotten wire as possible, but I also cannot find the right type of new connector with a pigtail to replace the whole length.

I hope these questions aren’t too basic or annoyingly novice. I know how finicky auto wiring can be, though, and I don’t want to mess it up. If I were repairing a lamp I wouldn’t be asking so many questions, but this is my baby.

Anyway, I appreciate any advice you guys have, either in answer to my questions or in general about auto electric repair (i.e. what I should avoid doing to prevent catastrophe). Thanks,


Go to your local Ford dealer. They can get you the correct pigtail for that sensor. Bring the vehicle and the vin number.

Getting the proper pigtail is definitely the best way to go, but the nearest Ford dealer is over an hour away in a town I never visit, so it’ll be a bit before I make it out. Do you think a dealer would be amenable to giving me a part number that I can order somewhere and have shipped?

I prefer a soldered connection over a butt joint. Not to say I don’t use them but I have had some fail in time even though I tug on the wires at the time, it seems some come loose.

Yes, in my experience the dealers should have no problem having the parts drop-shipped to your home. Call with the VIN number handy and they can look up the correct wires and have them delivered to your house.

It’s been a few years since I’ve had parts “drop shipped”, but I assume they still do it.

Butt splices work best if you strip off about 3/4" of insulation, twist the strands and then fold the wire in half. Us a barrel just slightly larger than the folded wire and crimp good. Most of the time a but splice fails is because the barrel was too big.

The fold in the wire will fan out after crimping making it harder to pull out.

Do a Google search for Contour or Mystique engine wiring harness. You will find that there was a closed-ended recall for the deterioration of the engine wiring harnesses. The only reliable repair is to replace the entire harness. In my experience once the insulation starts falling off the wiring harness is unrepairable. Replacement is the only long-term solution, but will cost more than the car is probably worth if they are still available.

@db4690, these harnesses are in the same league as the Benz “biodegradeable” engine wiring.

@Bluegill, you have internet, and there are lots of dealers on-line. I’ve had to order parts from the dealer, and found a few decent one’s online to avoid going to the local stealership.

Given the situation, I might be inclined to extract the pin from the connector and slip a length of heat shrink tubing over the wire. Shrink it and maybe apply some end sealer like RTV to prevent moisture getting in and calling it a day…

Thanks for the heads-up on the recall. I read this: “The insulation used for the engine bay wiring was not resistant to high heat conditions.” Which makes sense, as the wiring for the sensors near the exhaust manifold was the first to start going bad (that I’ve discovered so far). Sounds like, in the short term, I’m going to order the new pigtails from a dealer, splice them with a butt joint over the folded-over wire ends, and take a good look for more cracked wires. And start saving up for a new wiring harness installation (I’m not sure I have the experience or acumen to try tackling a wiring harness on my own).

Thanks again for all your excellent advice.

You might want to take a look at what Rockauto has if you are going to replace pigtails. They had a lot for my car with the specific connector and at a reasonable cost. My prefered method is to solder the wires together and use shrink tube over the connection to seal it.

I solder all automotive splice repairs. Splice crimp connectors are for aftermarket audio people.

Here is a splice repair procedure. I don’t always use the splice band but always solder and use shrink tube w/sealant.

You might also look for a way to insulate the wires from the heat radiated from the exhaust manifold.

Sincere best.

Thanks again for all the help. I’ve got the pigtails and supplies ordered, and they’re on the way. In the meantime, I’ve found some more bad wiring to take care of, this time leading from the battery positive terminal. I thought I’d make another reply in case someone comes here through the search feature or Google or whatever with a similar question.

The dealer was totally useless in helping me find the right pigtail. I did, however, stumble upon this helpful page from Ford:

It has all the Ford wiring connectors and the part numbers. What I did was take a picture of my connector, try to find the most similar-looking ones on that PDF guide, and then look them up on RockAuto. It worked like a charm; after looking up part numbers for five very similar-looking connectors, I found the right one. And thanks to you guys’ input, they’ll be properly crimped, soldered, and shrink-wrapped sometime next week.


I just remembered something amusing

An acquaintance asked me to check out her Contour, because it wasn’t running well and the check engine light was on

I hooked up the scanner and quickly realized there was a problem with the idle air control valve circuit. Upon closer examination, I realized that the entire wiring harness was so brittle, that anything you touched turned to dust

I told her I didn’t want to work on the car, because the harness was too far gone. I said I could make no kinds of guarantees with such a harness. I didn’t charge her anything, and told her to get the car out of my sight, please

The wire gauge is usually shown in the factory service manual’s wiring schematic. Do you have access to this document? If not you might be able to find it in a Chilton’s manual or at your local public library. Sometimes you have to convert between the two wire gauge systems commonly used in cars, one is the AWG system and the other is a metric dimension, I think it is the cross sectional area in mm^2. Make sure you keep to the same kind of wire, if it is stranded use stranded, etc.

When I have replaced/modified wires in my own cars, besides using the correct gauge, for places that get a lot of vibration and heat I’ll put a piece of heat shrink tubing on first, twist then solder the wires together, then slip the heat shrink tubing over the splice and shrink it with a hair dryer. I’ll usually top that off with some Scotch Super 33 electrical tape. Don’t frugalize on the electrical tape, those kinds you buy for $1 or 50 cents a roll aren’t nearly as good as Super 33. For the engine compartment, you definitely don’t want it unraveling in the heat.

In more innocuous areas where heat and vibration aren’t a problem I’ll usually crimp the wires together with a crimping tool. Sometimes I’ll crimp on spade-type male and female connectors on each wire, then hook them up that way. Especially if I thinnk I might want to disconnect them at some point for testing, etc. Solderless connections in other words. I’ll still often top it off with some heat shrink tubing or Super 33.


Amusing for us, but not for the guy with the Contour/Mystique who’s trying to keep his $500 car on the road and is being told he needs a $1300 wiring harness. I too have had the same situation, one look under the hood and I close it and tell the owner his car is beyond repair.

Let’s hope for the original poster that the wiring isn’t as far gone as we think it is.

@GeorgeSanJose Thanks for the tips. I noticed the cheapo electrical tape I had used for my temporary repair has already gotten stiff and brittle. Time to buy the real stuff I reckon.

@asemaster I’m kind of excited; I appreciate the challenge and the opportunity to learn more about car repair. I got a good deal on this pup and she’s only got 60,000 miles, so the game is to see if I can still get her to 150K even with time having a pretty good headstart. With my current job, I don’t need to drive at all and I’ve got nothing but free time during which to tinker. I might have a perverse desire for more things to go wrong, just so I have something to fix on the weekend (though I would appreciate having something easier to fix, like a coolant leak or a timing belt).

But seriously, I do appreciate the heads up on the wiring issues in Contours, so I know to keep an eye out for more problems down the line.