First thing first. Pull the instrument panel out, in the back you will find a heat shrink wrapped 2 wire connector. Back probe the connector with an ohm meter. Should be around 59 to 61 ohms. 60 is spec, but not final. Now remove that little 2 wire connector and measure resistance across the connector. Should be 120 ohms , give or take. The same with the harness end. Check part number of ECU . If it ends in 4402 plan on calling the dealer. Now, If that all checks out, move to your engine ECU mounted on bulkhead between radiator and engine compartment. Disconnect harness from ECU. Be careful, those old plastic clips might break if you get all savage with it.youve got to work the cam locks up n down little by little because they are probably packed with dirt. Once you get it unhooked, you want to disassemble the connector. On the top will be 2 twisted pairs orange yellow and green grey. You want to look closely where the wires run around corners. They tend to chafe and short out with long hours. You would also want to check connector @ engine harness connector. Looking closely for shorted wires.
If you look at schematics, you'll see that your instrument panel turns power on to second half of itself as well as vehicle and engine ECUs through a relay controlled by a resistor that acts as a delayed shutdown to allow computers to save information.
Good luck.
! The Volvo guys will be along shortly to help you out.
