Allison 4th gear lock up issues

[Gflanagan]

Pump is air shift. One light in cab for ok to pump. This light comes on when placed in pump gear. Have not checked the trans' shifter switch. Is this a neutral saftey switch or a 4th gear switch, I don't know how this switch is suposed to work if it has one. I'm going to work on it on monday, hopefully I can answer more detailed questions. Any advise on things to look for would be helpful. I've read that all these swiches and safty devices go to a relay, then to the transmission solinoids. I dont know what this relay looks like, where it is lokated or how to test it.