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:
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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?
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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?
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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?
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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
- Probably not
- No
- Yes
- I don’t know where the relay is. You’ll find it by following the tick-tick noise it makes when you hit the locks. Testing a relay is easily done with a voltmeter and a couple of feed wires… by why would you bother to test a 22 year old electrical part rather than just spend $5 on a new one?
Also. why are you only focusing on the electrical side of this? Have you considered that the latch mechanisms are both quite worn, likely filthy and in need of lubrication?
Thanks for your answers and comment Mustangman. Appreciate it. To answer your question on why test a 22 year old part… that’s half the fun of having a 22 year old vehicle. Learn something new and do it as cheap as you can. And all the door lock relays I’ve found for that vehicle are north of 20 bucks. Why spend 20 bucks on a gamble? 
Thanks again!
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I would remove both door panels to see what is going on in there.You could try spraying some lube at the actuator mechanism to free it…it works 80% of the time.
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Thanks for the input. Everyone seems to be pointing to mechanical failure over electrical failure. I’ll give it a shot and let you all know.
Thanks again,
DW
There is a YouTube video discussing a “cheap fix” for that door actuator. You sound like the perfect guy to give that a try, since you have had a fun game with doing repairs at the bare minimum.
Also, since the key fob and the interior switches behave differently, you may have a second weakness.
One question: what happens if you use the actual key to unlock the truck doors? That might be good diagnostic info.
Haha. Thanks for the encouragement! I’ll look for that video. As for the key, I don’t actually have a key for those locks. My key only works the ignition. If i ever get locked out, the back sliding window doesn’t lock, so I can just slide it open and send my kid through:)
Thanks for the reply!
You called this truck a beater . So why not just have 2 door keys made and be done with it . At least you can open the doors that way until you have the remote entry system repaired.
Then why worry fixing it? 
I noted a few other videos. I particularly liked one that “listened” to the relay clicks for lock vs unlock. That is such an easy test.