06-27-2018, 05:59 PM
These problems can be really frustrating and challenge our sanity. It will all work out.
The light has power continually provided to it by a common power source used all over the dash, what causes the light to turn on and off is whether or not the ground side is connected to ground by a relay that is triggered by the Allison ECU. You had indicated earlier that there was no voltage at the light. Without voltage to the light there is nothing for the Allison ECU to turn on and off. The electrical supply to that light is supplied by the chassis electrical and does not involve any Allison stuff.
If I were in your situation I would follow the power side wire from the bulb, it's an orange wire (the ground side is purple) in my 93 coach, testing at connection points for voltage until I found the open in the circuit. You can test the ground side, in the absence of voltage on the power side, by checking continuity to ground during initial startup or by throwing the "check trans" switch.
I had an instance in which a "check" light never came on until I found the power to it had been disconnected. I hooked up the power and the light would never shut off (probably the reason for the power wire being pulled. It turned out that the relay grounding the light was welded. I replaced the relay and had to rehook up the power before the light finally behaved properly. The techs probably tested at the relay and using a test box triggered it on and off through the ECU and declared it working properly (after replacing the defective one) and assumed that was the problem and never looked at the light itself.
The light has power continually provided to it by a common power source used all over the dash, what causes the light to turn on and off is whether or not the ground side is connected to ground by a relay that is triggered by the Allison ECU. You had indicated earlier that there was no voltage at the light. Without voltage to the light there is nothing for the Allison ECU to turn on and off. The electrical supply to that light is supplied by the chassis electrical and does not involve any Allison stuff.
If I were in your situation I would follow the power side wire from the bulb, it's an orange wire (the ground side is purple) in my 93 coach, testing at connection points for voltage until I found the open in the circuit. You can test the ground side, in the absence of voltage on the power side, by checking continuity to ground during initial startup or by throwing the "check trans" switch.
I had an instance in which a "check" light never came on until I found the power to it had been disconnected. I hooked up the power and the light would never shut off (probably the reason for the power wire being pulled. It turned out that the relay grounding the light was welded. I replaced the relay and had to rehook up the power before the light finally behaved properly. The techs probably tested at the relay and using a test box triggered it on and off through the ECU and declared it working properly (after replacing the defective one) and assumed that was the problem and never looked at the light itself.
Jon Kabbe
1993 coach 337 with Civic towed
