Customer had a stacked sat system. It was an old system that had 16 receivers and I guess at the time there weren't any multiswitches? Anyway I had never even heard of a stacked sat system. But he know wants locals so he needs the oval dish. So we install oval and multiswitch. 1 of the 16 rooms that have receivers has no odd transponders. But only when the lights in the room are on. Turn lights off and all channels and odd transponders work. Tried pulling extension cord around and plugging receiver into different outlets with no luck. Changed receiver, no luck. So it must be in the coax. Went in attic to make sure wire was not laying on top of light can, but our wireing is up and out of the way of all electrical. Is there any kind of ground isolation for coax that might help.

Anyone have any ideas?

Light bulb looking to the wrong satellite. LOL
Did you try swapping the receiver to see if the problem is with the receiver or the wiring?. Is the receiver an old Sony receiver?.

Is the coax grounded? What type of lights? If there is a ballast, It could cause larger magnetic fields. You could be getting induced voltage on the coax.

Swap recievers first to determine if it is the rcvr or the cable.

If the power cord uses a ground try lifting it to see if it solves the problem.

Regular light cans.
old sony receiver.
coax is not grounded.
3 prong cord.

yes we did swap receivers

Charlie did you measure the voltage on the coax? almost sounds to me like a nail partially through the romex and coax.

I assume you switched the coax to a different port on the multiswitch? Just to rule out the new switch. I just replaced a switch for one port with this exact problem, minus the light switch, devil, posessed factor.

You swap the receiver and still have the same problem right?
Did you swap the receiver that was in that room with another and the receiver works fine in the other room?
If Yes then it is no the receiver.
The new receiver that you put in that room was working in the other room?
If yes change to another port in the multiwsitch.
Did that solved the problem?
If not. Bypass the MS and connect the receiver direct to the LNB
Do you have signal now?
If not. change to another port in the LNB.
Do you have signal now?
If not replace the cable. You should have signal now?
Some older Sony receivers had a hidden menu to allow them to be configured to work in stack mode. Before you lose more time troubleshooting be sure that you have a new receiver and that receiver is configured properly.