The SAD fact: ALL original engine harnesses that Volvo installed in new 1980 to 1987 Volvos turned out to be defective.  They were all made with a poor plastic wire insulation that badly deteriorated after being exposed to engine heat.  These harnesses would fail after years of use and the owners of these cars have been forced to replace them or make repairs.  A few owners were fortunate and the defect was found during the vehicle warranty period (I have only heard from ONE owner over the years who actually had one covered under warranty, so I think that almost never happened).

WHAT IS A MAIN ENGINE HARNESS? 
A main engine wire harness is the part of the wire loom that goes to the many different points on the engine, such as the starter motor, alternator, engine sensors, fuel injectors, idle valve, etc.  On some Volvo, such as most mid to late 240 non-turbo models, the engine harness will extend through the firewall to an EFI computer (ECU or ECM).  On others, such as early 240s, 240 Turbos  and 700 models,  the engine harness will stop at a multi-pin connector at the firewall or fender, where a "body," "firewall" or "dash" harness then continues onward to other areas in the car.

LATER REPLACEMENT ENGINE HARNESSES
You will see the term "later replacement harness" used in places in this site.  This term refers to a new Volvo engine wire harness specifically produced to REPLACE an original defective harness.  A later replacement harness is not just another identical original Volvo wire harness.  If it was, it too would eventually disintegrate after exposure to engine heat.  The wire insulation defect was eventually recognized by Volvo and corrected just prior to production of the 1988 model year.  So the rotten insulation problem essentially became cured for all 1988 and later Volvos.  Later replacement harnesses were manufactured using better insulation, designed to handle the prolonged high temperatures under your hood. 

Nearly all later replacement harnesses made by Volvo were given NEW PART NUMBERS to distinguish them from the old bad harnesses.  A new part number is how you can tell for certain if your car already has a later replacement harness. 

<<< Finding Your Part Number: Most part numbers will be found on a red tube as shown here, however it is not always found in the same place on every harness.  For more detail about finding part numbers, CLICK HERE.

The factory original engine harnesses installed in all Volvos during the 1980 through 1987 model years started to disintegrate after a few years of exposure to engine heat.  The insulation on individual wires would get soft and crumble away, eventually leaving exposed wires to short out and cause all kinds of problems with electronic systems.  This problem is caused by HEAT attacking the defective insulation over many years of use, and was somewhat accelerated in turbocharged cars due to the higher heat in the engine bay. 

This defective insulation problem DID NOT plague pre-1980 Volvos, nor was it found in 1988 and later cars. 
The defect period was only 1980 to 1987 models.
Volvo eventually recognized and was able to correct this problem for all 1988 and later model engine harnesses.

If you're the owner of one of these Volvos, this could very well be the cause of intermittent failures.  These harnesses connect to such components as engine sensors, alternator, starter motor, fuel injectors, throttle position switch, idle control valve, mass air sensor, fuel pump relay, oxygen sensor, ground points, control pressure regulator and cold start injector.