I have a '98 f150 reg. cab xlt, flareside box with a 4.6 abd 5speed. I got in today and started it up and heard what sounded like a relay clicking. After looking around I noticed that the marker lights(not 4-ways or headlights) plus the dash lights were flashing. They would blink about once every 5-10 seconds. I pull all the relays on the inside and all the ones in the 2 boxes under the hood, none would stop it. It wouldnt start until I started the engine and if I shut the engine down it would take about a minute for the flashing to stop. If I turned the headlights and marker lights on there was no more flashing, but I can still hear the relay clicking. If anyone has any idea please let me know. I hope this is enough info, if you need more let me know. Thanks alot everyone.

Forgot to add, there were also flashing red and green lights next to the inside fuse box. Thanks again.

 

Sounds like you might be having some sort of problem with an alarm system. Is you truck equipped with an alarm? Is it factory or aftermarket? Some of the aftermarket alarms have relays that hang loose under the dash. Have you been able to find the relay that is making the noise?

 

I havent found the relay yet, but it did stop doing it now. There is an aftermarket remote start and keyless entry on it. Not so sure if it includes an alarm system. I'll have to ask the previous owner and see if they know of any relays under the dash from it. Thats a big help. Thanks alot.