2005 Ford F-150, Starts with Viper 160XV, But Not Just Using Key In Ignition

2005 Ford F150 5.4 XLT. Viper model 160XV. I also have a DEI 556U immobilizer interface and a XCRS relay satellite box. Intermittently key will start truck but other times only using the aftermarket remote start key fob will start it. When trying with the key if it won't start all kinds of stuff in the truck start clicking on and off. Some reason the flashers go on and off although the flasher lights on the dash never come on. Also never seems to make any sound that the starters trying to turn over when the key won't start it. But I can sit in the cab and lock all the doors and actuate the remote start fob and it will start right up like no issue. I can then turn the key on and the truck will run although the flashers keep flashing on and off for another minute or so. So I just bought the truck and I knew it had this issue so I don't have much history on it. Other than supposedly most of time it used to work just fine off the key and in fact I drove it home and it started quite a few times with the key. But now once again it seems the only start with the remote fob. The remote starter is an aftermarket add-on, so I'm thinking there could be some kind of wiring issue with it. Hoping maybe somebody's had experience with this in the past and can direct me on what to look for. Thanks! Update 1: Forgot to mention the horn also goes off during this time I forgot I unhooked it cuz I got tired of hearing it. After realizing that it got me thinking this actually matches what happens when the panic alarm button is pressed not sure why that would be going off. Just putting the key in and turning on the ignition. Maybe this will help with the diagnosis.p Update 2: so yesterday I decided to check the anti-theft light on top of my dash I noticed it flashes red all the time with the vehicles turned off . When I turn the key on, it goes solid red for second or two and then goes out. I'm assuming this means my Pats security system is working correctly. Truck is still not starting with the key However also observed that when I turn the key on and the flashers start going off and I suppose a horn would be honking but I have it disconnected that the buttons on my viper key fob will shut it off using the lock button. Maybe even the unlock button anyhow buttons on it work but the lock and unlocked on the factory Ford key fob does not seem to affect it at all. So I'm assuming that means that the viper alarm system is the one generating this panic alarm. I finally figured out all the model numbers of my aftermarket alarm system it's a viper model 160XV. I also have a DEI 556U immobilizer interface and a XCRS relay satellite box. The good news is the immobilizer probably has another key that fits my truck as I only got one with it. So maybe now I have two. If I ever get the truck to start with just the key I can program another key. So my Hypothesis is right now that the remote starter box must somehow be interrupting the circuit to keep my starter from engaging. I know the starter wire has been cut to install the remote starter system, but I don't understand how it works fine with the remote but apparently it's not passing through the signal when not using the remote.2005 f150

Seems like the Viper is triggered which is causing all the lights and horn to go off. Viper would most likely prevent key from starting especially while it's actively going off. The Viper injects the starter power from the starter side of the cut key start wire so that makes sense that it can remote start while the key can't. If the Viper remote is not disarming when you press unlock it's FOB then that may be your issue. Do the doors unlock from the Viper remote?Steve G

I'm at work right now so I can't check it but I have noticed that at times it seems like it doesn't do anything. I also noticed yesterday when it wasn't working that sometimes even the horn and lights are not flashing but still did not to work. Also, is there anyway to disarm the viper so that it would not interfere with normal starting procedure?2005 f150

Well when it doesn’t unlock via the viper remote then you aren’t disarming the viper alarm. Usually there is a small push button either mounted somewhere near the viper brain to manually disarm. If you gain entry to the truck though without disarming then the alarm will trigger when you either open the door or you turn the ignition key. But the start wire for your key will be interrupted while armed or triggered. When the viper unlock/disarm doesn’t work, what do you do to enter the truck? Do you unlock from the cylinder or use a factory fob remote?Steve G

Well that's a good question. Maybe it's all operator error since I've never had this system before. Sometimes I think I've used the viper key fob and other times I've used the Ford key fob as I got both of them on my key ring. I have another vehicle with remote start. I guess maybe it's never had an alarm. I've never really paid that much attention. I've always used different key fobs for it and never had an issue, but that could be the whole issue here.2005 f150

Perhaps the Ford key fob should remain off your key ring for a bit and try just using the Viper one for a while to see if the issue stops. If installed properly the door key should also disarm the Viper alarm. If you decide you don’t want the Viper you could pull the fuse for the viper brain but you will need to reconnect the starter wire so you can restore full time function to the key starter wire.Steve G

Yeah, sounds like I need to do some investigating. Thanks for all your replies. I appreciate it.2005 f150

When about 3 days Just using the Ford fob It seemed to work and then it quit again. Today it started working again. I swapped back and forth between the viper key fob and the Ford key fob. Both of them seem to work every time. I then noticed something odd. The viper key fob didn't seem to want to lock the doors. You could push lock in the first time. It made kind of a relay noise but nothing locked. You could keep pushing lock but nothing ever happened but then you could push unlock and it would try to unlock it and then you could push lock and then it would start working again.2005 f150