Gas Recirculation Valve (egr Valve) problems of the 1999 Mercury Grand Marquis

Intake manifold failed (burned and disintegrated in the area of the thermostat ) and had to be replaced at considerable expense . Presently the speedometer fails intermittently dropping to zero at random moments. Most importantly the lights cut out intermittently usually when the heat is on and on longer trips. Also, most times it has happened when it has been raining and colder. Drove upwards of 40 miles with the headlights cutting out intermittently in the rain and cold, problem has continued to recur but seems to be related possibly to having the heat on. I believe the lighting control module is located near a heating outlet and may be suffering a failure as a result but this is just speculation. Also, previously when I had pulled into a rest area for awhile, after cooling down, the problem went away for a little while then resumed after about ten miles with the heat on. I believe it is being caused by the excessive heat the lcm is subjected to by virtue of the area in which it is installed. The lighting control module is of motorola manufacture with siemans relays inside. The part has numerous numbers on it , most prominently: xw7t-13c788-aa , 6mx2794a01, 990429a, and lighting control 95m . Others online with similar vehicles (crown victorias) and of other model years manufactured by Ford have reported similar problems and that replacing the relays has resolved the issue. I do not know that this part is the source of the problem but suspect it as many others online have reported that this part was the source of their problems.