unfortunately, light came back on whilst driving home last night. looks like its a costly one.. 

If tinkering with the fuse turns the light off, even temporarily, then you are on the right track. 

I'm thinking it's got to be a wiring issue, or quite possibly the aftermarket parts being poor 

Unfortunately, I have the same problem, I changed the pump with a commercial one, but the problem remains, fuse 29 seems good, how did you solve the problem?