When you are starting the ignition switch bypasses the relay allowing it to start when you release the key back to the on position the relay is suppose to take over,and keep the motor running.

 

You should have 12V on the battery side and roughly 10V on the fuel pump side, measured to ground.
If there's no voltage to the ballast resistor, the fuel pump will run with the key in "start", but not when it's "on". (there is a relay up front that powers the fuel pump directly to start the motor)
If you are certain there is only 0.03V at the resistor with the key on, follow the wiring from the resistor back to the ignition switch. Particularly any plugs/connectors that pass through the firewall.

 

Its simple just swap relay the 4 square ones in a row by the battery,with one another and see if it starts I know it will I'VE BEEN THERE!

 

so i went out today and looked at it and while i was looking around the relays i saw an orange wire by the ignition relay that looked burned. Sure enough it burned through and was disconnected so i temporarely connected it and tried to start my jeep and it worked!!! it stayed running. I then cut the wire off my parts xj and cut the old wire off of mine and spliced them together perminantly. Just another reason why its good having a parts jeep sitting in the yard. Thanks for all the help getting it running. I dont think i would have looked in that area had my attention not been drawn to the relays. Its great having my xj back! ill post a few pictures of exactly what im talking about when i get to it if anyone is inerested.

 

fuse able link burnt?

 

Always gives me a a good feeling knowing an xj is back on the road

 

the one on the right is the old one that burned through and the one on the left is the one i replaced it with from my parts jeep. The wire connects to the ignition replay where the smaller positive terminal of the battery connects and many other things. Hopefully the attachment works

 

Those are the fusible links. They are just a short section of thinner wire that protects the harness they feed, designed to burn open if there is a short.

Nice detective work!

 

Couldn't the fuel pump resister/relay unless its bypassed once you turn the key to the start position .....

 

there are reasons those burned out click the link in my sig and do a ground refreshing and read though the Renix tips for cheap insurance...
hopes this helps you

 

Thank you for this thread. I was completely stumped and ready to give up. Then I found this thread. Saved my life. I had the exact same burnt fuseable link. Fixed the problem.