Electrical Issues

[Robb]

My 7 has always had a wierd electrical issue with the manifold gauge and magnetic compass. When I key the mic the Vans manifold pressure gauge slowly drops to zero when transmitting. As soon as I release the mic button it goes back to normal. If I turn on any electrical components such as strobes or landing lights the compass turns around 40 degrees ? Any ideas before I try an avionics shop?

[RVDan]

Let me give this a try. The manifold pressure gage is likely being affected by RF from the com radio. First place to check: Either the manifold gage or sender has a bad ground or connection on the sender leads. Check these out. If that doesn?t solve it, there might be an antenna ground or cable problem. Do you have dual coms? Does it happen on either com?
On the compass, is it a wet compass or a compass with a magnetometer?

[Raymo]

When you key the mic (PTT), you are making a connection to ground via the PTT switch, which tells the radio you want to transmit.

I agree that this is likely an issue with grounding of your MP gauge and/or sensor.

The lights/radio issue is probably not related. You'll want to determine where the nav/strobe light wires are located in relation to your compass. If they are too close and not twisted (power and ground), you'll want to move them as far away as possible and put a twist in the wires (see Steinair videos) to help cancel out the interference/magnetic field being generated.