Hi: I'd appreciate any words of wisdom to diagnose the power locks on my 1998 F-150 with 4.6 liter engine. It's got over 200k miles. It's a beater in the true sense of the word.

Symptoms:

-The key fob works to lock and unlock both doors (it will make the clicking sound ALWAYS and send current to the actuators, however about 1/4 the time the passenger door doesn't seem to push the lock up fully. In those cases, a few more hits on the key fob will make it unlock).

-The door switches on both doors will always engage the actuators to lock, but neither switch will unlock the doors -- when I push the unlock switch on either door, 99% of the time nothing happens. I have had random success holding the switch on the driver side down for 10-15 seconds and then pushing it down again repeatedly and it will unlock both doors. However, that is not consistent and not reliable.

Questions:

1. Could a weak actuator on the passenger door cause the door switches on both doors to fail only on the unlock selection, even though the key fob always sends current to the actuators?

2. It does seem that I have a weak actuator on my passenger door due to it not pushing up fully much of the time, but does that have anything to do with both my door switches not making any sound or doing anything only on the unlock selection?

3. If one time out of a hundred the door (unlock) switches do engage the actuators and make it unlock, can I rule out the switches being bad?

4. I've seen some forum posts that make me think it might be a bad relay under the dash somewhere. Any thoughts on where it is located on my truck and how can I test it without having a fancy circuit tester?

Any words of wisdom to help pinpoint where the issue may be would be most appreciated.

Thanks much,
DW