no pilot meaasge

Hi, My S1 cc was again dead with a sea talk fail message and .4V on the yellow wire. S1 and 6002 alone. I know Raymarine will not even look at it. I found a used S3 on ebay. Now I get a No pilot message. S3 and 6002 alone. But the voltage is between 7.5 and 10.8 on the yellow wire. Would someone...