Relay Chatter When Wiring to Dome Light

You are sending a pulsed ground to a coil and magnetic switch. Capacitor should be on the 85 and 86 to smooth out the dome light circuit ground dimming pulse. A diode may also be needed to keep the capacitor from back feeding the dome light circuit ground. Band towards the vehicle side. If the lights stay on to long after the dome circuit goes off use a smaller value capacitor.

i am an idiot wrote: Capacitor across 85 and 86.

Agree. Changing the capacitor to be across the coil (85-86) should improve ir.