I've been sorting out electrical problems on my neighbor's Caterpillar E70B excavator (s/n 5TG00128). I was able to successfully replace the fuel level gauge and hydraulic temperature sending unit, but can't figure out the warning buzzer/idiot light arrangement. Here's what it's doing: -With key on/engine off, the charging light is on but no other lights/buzzers -With key on/engine running, the same charging light is on, but no other lights/buzzers The machine operates as though nothing is wrong. All the gauges are working. The charging system seems to be working fine (26+ V running). When the 'test' button on the dash is pressed, all the warning lights come on and the warning buzzer sounds. I've checked the circuit to each of the sensors and all are in working order. In fact, when I shunt the coolant temp sensor, the light comes on in the dash and the warning buzzer sounds (as it should). However, the oil pressure light does nothing and the charging light will not go away. I've even replaced the main circuit board under the gauges/lights with no change in symptoms. Stumped!! -Jake
Photo added -Bump- I'm also adding a photo of the panel in question. Also, the Caterpillar 307 SSR excavator has a very similar dashboard arrangement if anyone has experience with those? Could the engine speed sensor be bad? If it's no good, the panel would not know the engine was running. And the panel would not display the oil pressure light until the speed sensor saw motion? What do you all think? -Jake
Well I was able to test the engine speed sensor theory. I checked for voltage using my DMM across the two wires while the engine was running. At low idle it showed approximately 13.5 VAC. At about half throttle it showed approximately 18.8 VAC. Therefore the sensor seems to be working fine. Any other ideas? I'm really stumped on this one. Thanks, -Jake
The testing procedure is a little involved but in a nutshell; With the engine running, check for voltage at the white/yellow wire on the alternator. It should be 14v. (The manual doesn't specify it, but I'm guessing this might be ac.) That wire goes to the safety relay. Find it. I'm not sure where on the machine it is but in the picture it looks like an aluminium box with two hold down screws, heat-sink fins and a flying lead with maybe 5 wires. Check you're getting the same voltage at the relay. If all is good so far, unplug the relay. If the light goes out then the relay is faulty.