Wiring Harness Guide

So, why would you ever go to this insane amount of work? Because you are either 1) Poor 2) Cheap or 3) Insane. Wiring harnesses generally need to be replaced on all 1980 to 1987 Volvo’s because the plastic wire coating breaks down under high heat. On a turbocharged car, many wiring harnesses have already been replaced, since the high heat conditions of a turbocharged motor expedite the disintegration process (i.e. heat = bad). On N/A (normally aspirated) motors, I have seen wiring harnesses last for 250 to 300 thousand miles or more. Or a lot less.

While all the wiring in the car is vulnerable to heat degredation, only the wires exposed to such temperatures actually degrade. These are generally only the engine wiring harness and the few wires that go to the transmission. You can tell that your wiring harness is going bad by looking at the wires in the engine compartment. They are easiest to see on the firewall, just below the windshield, coming off the big grey plastic clip. If the wiring coating is crumbling, cracking, and can be rubbed off the copper wire by rolling the wire in your fingers, you probably need a new harness. Another place to look for bad wires is by the alternator.

While replacement wiring harnesses are readily available (from Volvo and from aftermarket suppliers) they are EXPENSIVE. Even used replacement wiring harnesses pulled from junkyard cars sell for $100 to $300 because of the grueling amount of work that is required to pull out a wiring harness at a junkyard. My dad got bit by a spider when he was pulling one, so what was that worth? Who knows…

Good places to get a wiring harness are from Dave Barton (used but much cheaper) from Swedish Engineering or IPD (new and expensive) or from the Volvo dealership (most expensive).

Parts List

An alternative method is to build your own damned wiring harness out of materials that you can get at any car parts store. Here is a list of materials you will need to do this job:

* 100ft of 16-gauge wire ($10 to $12)
* 6ft of 8-gauge wire ($5)
* 2 8-gauge ring terminals (1/4″ inside diameter I think) ($1 to $2)
* 50 pack of 16 gauge butt-connectors ($5)
* 10 pack of 16 gauge ring terminals ($2)
* 10 pack of 16 gauge shielded spade terminals ($2)
* 10′ of heat-shrink tubing ($5)
* optional: 20′ of corrugated wire wrap (black plastic stuff) in different sizes ($10)
* 2 rolls of black electrical tape ($3 to $5)
* Intake manifold gasket ($6 to $20 (aftermarket vs. Volvo))
* Zip ties ($2 to $5)
* A good pair of wire crimpers (probably $25)

The 16-gauge wire is for all the little wires, the 8-gauge wire is for the thick wire that runs from the starter to the alternator. I got the 6ft of 8-gauge and the two ring terminals in a package from Car Quest for about $5.50.

Spend the extra money and buy quality butt/spade/ring connectors and wires. Car Quest usually carries a good brand like Nobel or Pico. Don’t get those generic butt connectors. They have less metal in them and don’t seal as well.

Get a GOOD wire crimper.
Don’t use one of those $5 red-handled generic ones or your hands will hurt after a few hours from how hard you have to squeeze and your crimps still won’t be very strong. I paid $25 for a Noble wire stripper/crimper and it’s been great. A good tool to have for installing stereos as well.

You can buy all one color of wire in a spool (cheapest) or try to duplicate the colors of wire that Volvo uses. This is more expensive, but will be easier to keep track of during the harness-building and will be easier to test after it’s all together. The only wire colors you might have trouble finding are the striped wires, which are red/white and blue/yellow. The other colors are fairly common: white, red, orange, yellow, green, blue, brown, black, and grey.

Building The Harness

Plan on spending about 16 hours working on this, assuming you’ve never done it before. It’s a long process, and there’s no point in rushing because one mistake could cost you another 8 hours of work to find it and fix it.

Taking off the hood makes this job way easier. It’s only 4 12mm bolts, but you’ll need two people to lift it. Just set it on a towel or piece of cardboard and lean it against a wall.

Disconnect the battery so you don’t kill yourself or start a fire.

First, take off the intake manifold and detach all the stuff from it (making sure to mark it all with numbers and tape so you can remember how to put it back together). Drawing pictures helps. Intake manifolds vary by the car – there are three types that you will run into depending on your car. The hardest to take off is the B21F manifold, as the bolts are the hardest to get to. On this manifold, you will need a regular 13mm wrench as well as a ratchet with a 1 ft extension to get it off fairly easily. The other manifolds are much easier.

Do not damage the old wiring harness. You will need it later.

Once the manifold is off, disconnect the old wiring harness from everything it’s plugged into. Get it at the starter, the alternator, all the engine sensors, and the big grey plug on the firewall. Make sure that each plug on the wiring harness is labelled with tape or something so you know what it goes to. Some connectors can be accidentally swapped, although most are uniquely shaped.

Pull out the old wiring harness (easier said than done) and then put a big piece of cardboard over the engine compartment to use as a table. Better yet use a real table or a workbench. Some people have nailed the old wiring harness to a wall to keep it from moving around. This works pretty well.

Next, go step by step and copy the old harness exactly, using your new spade connectors/rings where applicable and use the old square black connectors when you need to. To do this, cut off the old connector leaving about one inch of each wire coming out of it. You’ll need to do this on the big grey connector at the firewall too.

To reuse the connectors, connect the little bit of old wire to the new wire with a butt connector. Before you crimp down the butt connector, slide heat shrink tubing over wire so that you can pull it back up over the butt connector once it is crimped. Now, crimp the butt connector down good and hard. Check the connection by firmly tugging on the wire.

Now, slide the heat-shrink tubing over the whole thing so that the butt connector AND the old wire near the square connector are covered. Now shrink that tubing! I used a lighter, but a hair dryer or a heat gun works better.

When you’re measuring the replacement wires on the old harness, don’t make the new harness much longer. Maybe make each wire an inch longer MAX. Otherwise you’ll have too much extra wire flopping around everywhere.

As you go, use electrical tape and wrap things up to duplicate the “branches” of the old wiring harness. You’ll have to think carefully to do this, it is kind of hard to keep track of everything at once. You can use however much electrical tape you want, the more the better. I double-wrapped my whole harness. Now, you can cover it in that corrugated tubing if you want. Installation is, of course, the reverse of removal. Make sure you labeled your new harness too so you’ll know where to plug things in.

Enjoy! You just saved several hundred dollars. Of course, if you had worked a good job for those 16 hours, you could have made enough money to buy an aftermarket harness. However, if you like working on cars or are broke, unemployed, un-employable, or have a low-paying job, then this is the way to go.

Let’s hope you did everything right. I’ve done this three times now and it has always worked great, but if you start the car and fuses start to blow, just remember:



Good luck!