The ABS system has nothing to do with the spark plugs and wires unless, in very unusual situations they are radiating signals that are picked up by the wires going to an ABS wheel speed sensor. Ford trucks are the only ones that have a little trouble with that. When the ABS warning light turns on, there will be a diagnostic fault code stored in the computer's memory that will lead to the circuit or system with the problem, not necessarily the defective part. Those codes are the starting point in the diagnosis of the ABS light.
It is very rare to need an entire wiring harness for any circuit in the car unless they are sure it is the cause of an intermittent and hard-to-diagnose problem. That is something mechanics fall back on when they don't know how to diagnose a problem. Multiple melted wires, such as after an engine fire, would be the exception. If they found bare wires or wires touching each other, they found the problem and things like that can be fixed without replacing the entire harness.
As for the Check Engine light, the same goes for stored diagnostic codes in the Engine Computer. Since it came on right after ignition system parts were installed, the logical place to start looking is with those parts. There are a lot of aftermarket parts that work just fine in most applications but have some little quirk that makes them not work right in a few applications. Volvos use a lot of weird parts and it may be necessary to use original ones. In most states, shops are required to give you your old parts that were replaced. If you have them, you might ask the shop to put them back in since they weren't very old and didn't solve a problem.
Tuesday, November 30th, 2010 AT 5:01 PM