Hopefully this can help others, i have had an electrical gremlin in my S250 for at least 12 months. It would work as normal an every so often shut down, key off then back on it would run. It got to the point that it stopped working all together.
I spent days fiddling, cleaning earth connections, inspected the fuse box, grabbed the main harness and gave it a shake, every so often it would light up. Start then run for a bit and stop...
Long story short, i had a mate come over 2 weeks ago with his power probe. He was looking at the right hand panel and noticed the panel came on for a moment. Voltage at the red wire on the key switch was 12v, battery voltage was 14, so 2v drop right there. Key on (bridging red and white wires), the 12v dropped to 5, no panel life. Using the power probe, he injected 12v into the red wire when key was on, the panel lit up. We ran two new grounds, one from each panel to the chassis, as the resistance was 40 ohms to ground, dropped to one after that.
The fix was to open the panel, bridge the connection from fused power to the panel to the red wire on the switch connection. This could have been done externally by tapping into two wires, but we wanted to be sure there wasn't an obvious burnt component or trace. It appeared the trace ran across a low resistance resistor between two pins, so figured it was fine to by-pass it.
Previously there was an issue with a high charge pressure warning, this appears to have been resolved (more testing needed though), possibly due to low voltage to the panel, i'm not sure, time will tell. Pressure was tested with a gauge and was within spec, a good sender was tested in it's place, same result before the fix.
I'm glad the service manuals still come with wiring diagrams, without it, it would have been a far harder job to trace.
I spent days fiddling, cleaning earth connections, inspected the fuse box, grabbed the main harness and gave it a shake, every so often it would light up. Start then run for a bit and stop...
Long story short, i had a mate come over 2 weeks ago with his power probe. He was looking at the right hand panel and noticed the panel came on for a moment. Voltage at the red wire on the key switch was 12v, battery voltage was 14, so 2v drop right there. Key on (bridging red and white wires), the 12v dropped to 5, no panel life. Using the power probe, he injected 12v into the red wire when key was on, the panel lit up. We ran two new grounds, one from each panel to the chassis, as the resistance was 40 ohms to ground, dropped to one after that.
The fix was to open the panel, bridge the connection from fused power to the panel to the red wire on the switch connection. This could have been done externally by tapping into two wires, but we wanted to be sure there wasn't an obvious burnt component or trace. It appeared the trace ran across a low resistance resistor between two pins, so figured it was fine to by-pass it.
Previously there was an issue with a high charge pressure warning, this appears to have been resolved (more testing needed though), possibly due to low voltage to the panel, i'm not sure, time will tell. Pressure was tested with a gauge and was within spec, a good sender was tested in it's place, same result before the fix.
I'm glad the service manuals still come with wiring diagrams, without it, it would have been a far harder job to trace.