After running headlights for 15 to 30 minutes, my dash lights and parking lights begin to flash on and off in a steady and consistent pattern. If I power off the headlight switch for a few minutes, the flashing pattern does not return for approx. another 15 or so minutes. The headlights themselves do not flash, only the parking lights, tail lights and dash lights. Turn signals and 4 way flasher operate normally at all times regardless of status of this problem.

Other clues: At highway speeds, the problem may not not show up for an hour or so, or on rare occasions, even longer. When in stop and start traffic, the problem occurs sooner. It is happening more frequently now, whereas in the past, it was more intermittent.

When this occurs, I use the switch reostat to dim the dash lights to lowest setting - no effect on exterior lights.

I suspect it is heat related, as the problem goes away temporarily when powered down. I doubt it is a bad ground because once it starts, the flash pattern is too consistent, almost like it was regulated. It is not a flicker or of variable intensity.

I replaced the headlight switch last year as part of another troubleshooting activity, but anything/everything is possible now.

All other auxiliary lighting, both exterior and interior, is powered by individual circuits independent of the headlight switch or other factory source.

The headlights are sylvania 55 watt halogen upgrades over stock. Vehicle is a 1980 F-100 short box flare-side with 351M, C-6, 2WD, no a/c, Dura Spark 2 with all electrical system components new or upgraded within last 12 months.

I would appreciate any suggestions or comments. If more electrical system info is required, please advise. (No rush - I will be in hospital for next 2 days, so I won't be able to check for any replies or provide any more detail until I return home on Thursday (God willing))

Thanks in advance,
JT

 

Headlight switch or the plug that plugs into the headlight switch. Look for discoloring of the pins and their mates.

 

That is unusual that the headlights stay on, but the parking lights blink on and off. The circuit breaker that could make them blink is on the headlight circuit. The parking lights are on a fuse. Anyway, I would definitely do like subford said and check the switch and the plug out.