I have a 2006 Volvo EC290 excavator. It runs great, and recently had a new SinoCMP ECU installed (by me) a long with a wiring harness patch for the three hydraulic switches on the main block and new switches installed. So far the new ECU fixed the idling problems. I noticed that the lights are not working. Not the boom ones, and not the cab ones (the 'headlights'). I just got this maybe a month or two ago, and don't remember trying them. They may have worked on the book, but it may have been my other Volvo im thinking of. I swapped ECUs to the broken original Volvo. No change, no lights. I checked the fuses. All have continuity. I swapped all the relays behind the seat. No change. The bulbs in the lights are good. Not really sure what else to do... the parts catalog shows the partial wiring harness, and from what I can see, the only involved parts are lights, the relay(s), and rocker switch. And of course wiring. There is no evidence of mice or wiring back work. I also swapped the headlight switch with my other Volvo, no change. I also noticed that none of the rocker switch lights work. I pulled a switch, swapped the bulb with a. 12v version (I think these are supposed to use 24v bulbs??) And nothing. I checked the voltage to the bulb holder, nothing. Tried a few switches and none have power. Possibly related to no lights problem? These ARE supposed to work, right? It's the same switch used in older Volvo cars, the light goes on when the switch goes on. Also, the radio doesn't work. Fuse good. I have not checked voltage yet. Also possibly related? Tried with music switch on and off, no change. Any help would be appreciated. Volvo dealer/techs are an absolute rip off. Minimum $1k charge just to diagnose around my area. Unrelated question: I threw a new instrument panel lens cover on, and put the temperature needle back on (it was rattling around). I noticed the temperature shot to the red, but it is not overheating. It seems like the pin itself on the gauge must be almost spring loaded to calibrate it? So I need to twist the pin back, then put the needle on. I tried this and now the gauge reads a little less than 3/4, still high but again not overheating, I think it's the needle.
Specifically, what model and serial? For example the B series had 3 sub generations. It helps to know what you have.
Tag on cab is EC290V12492 Did some more testing. Radio has voltage so radio must just be bad. The light switch has 25 volts, so the switch has power.
So, for starters, the relays behind the seat or for HVAC. You want to look above the battery. A large plastic cover with 4 bolts, remove that. A smaller plastic housing with several connections hanging off it. Take that cover off, carefully. The guts have probably all fallen apart. Find relay 3501, for lights. If that's not the initial problem, look at the connectors beneath it. They're known to trap water and corrode. I also attached the diagram for your radio. Again the 24/12 is in the same area. Good luck.