I know a lot of people will blow this off. But the grounds on the engine to the frame are espeacily important. Their is a lot electronics on top of that engine. WIthout the proper amount of grounds they tend to send dirty power back into the batter packs.
I work on the f16 avionics package as well as all of the com nav as well. A lot of our dirty signals on the radios tend to be a ground that is not working properly on that direct system or another system putting feedback into the power system due to bad wiring. for instance if your supposed to have certian wire type with a certian amount of impeadence and you just go to walmart and grab just regular old copper wire. That is probably your problem. the way to tell on that usualy is strand size and if color. If its silver you need to find out what it is and try to find some more of it. but coper is coper. as long as your not trying to use solid copper wire from a house.
One thing to check is make sure that your not running to many auxilry systems (cb, amp, inverter, things like this) off of the same ground or the same power source. I have a dp tuner as well with no issues. I didn't like the instructions on that harness. So I improvised. any time you take a wire and bend it beyound its limits its lifespan is shortened. So I took a 5/8 drill bit and made a hole on the end of the pcm housing(the black plastic that holds the pcm in place). Right were the harness would come out. this way It was a Direct shot to were ever I wanted to route the harnes, with no bad bends.
For all of my added electronic goodies I made sure and gave them their own power. (Not Tapping off of other Sources power). The only thing I tap off of is for a trigger wire to latch my realys to route the power where I need. The easy's way to do this is grab a driving light wiring kit. THeir about 15 dollars or so. The reasoning in doing this is it takes a small current to latch a realy so the system your stealing from doesn't notice it. As well as it still can supply a large amount of power to what ever you need. But if you have no extra stuff I would inspect all the grounds you can find. I know a lot of the stuff thats in the dash area has grounds behind the fuse panel cover. The big plastic piece you pull to find the fuse box. If you look to the right side of this you should see a cluster of grounds their.
Another thing is make sure that the wiring harnes that goes across the parking brake release handle is not chaffing and sending a signal into the chassy. I had to repair mine. This harnes comes in the cab just to the right of the pcm. It actuly has a couple of plastic clips to attach it to the computor mount. it then makes a turn up for the center of the dash. this is were it rubs on the parking brake handle. It was causing just well Odd and unexplained things to happen. I will try to get a picture posted later of what Im talking about.
I have a 1200 watt amp behind the seat, rear electric seat that turns into a bed, 148gtl cb, xm radio, and a auxilary battery in the bed for my trailer winch. all with no interfence. so I must have somthing going for me.
But every electric problem is different I just hope to shed some light on the worst problem to work, Radio INTERFENCE!