Power Antenna with Mind of Its Own -- ECU or ?

[greentruck]

I haven't had a lick of trouble after installing my head unit in the 80. At the time, I was still new enough I R&Red the whole power antenna, when I could have probably just done the nylon cable. In any case, the power antenna has worked like it should for a 97, with manual control of height and memory so that it return to the preset height when swicthing to radio. So everything's been working OK, until an incident about a month ago...

I was driving along listening to the SAT radio on Aux when all of the sudden the head unit switched its source to the radio and up pops the antenna. Hmmm, I thought, then nothing more, thinking it was just some odd thing. I will note this was the ONLY time it actually switched sources while running.

Soon I started noticing that the radio would come on when I started up, when I swore I was listening to SAT or USB sources. I confirmed that as an issues simply by paying attention...


What's weird is that it doesn't always revert to the radio on restart. Sometimes it does, sometimes not. And it's never done it again driving along like the very first time, just at restart.

I read through the most seemingly relevant threads, but nothing like this. It's more in the realm of irritating than a big deal. Everything works except it loses its mind from time to time. Yeah, I'm getting old, too.



Since it's intermittent, I'm thinking maybe a sticking relay, but that's just a WAG. I'm thinking the failure is specific and limited enough that it might be easily diagnosed. Then again, it is an electrical gremlinAnyone have a suggestion?

 

[Eicca]

Haunted.















Do your radio presets get wiped when this happens?

 

[greentruck]

Nope, no standby power lost to the radio itself. The presets, etc all stay in place. Just the spooky antenna.

On the other hand, obviously powering up the operation side of the radio on restart might have something to do with it, since that does -- on its own schedule -- cause the change in source in the head unit.

 

[Eicca]

My limited experience points to either a short in the wiring somewhere (no actual idea where) or a defective head unit.

Wish I could be of more help, but hey, you get a thread bump

 

[greentruck]

Eicca,
Yeah, thought about a short. I usually do a pretty good job on wiring, but s# happens. I'd guess the blue wire or whatever it is that provides antenna sense. That was something apart from the other wiring. Hate to pull the dash apart to "visually inspect" something that I'll change by both taking it apart and putting it back together.

Unless something more obvious or hard to put up with happens, I'll just keep hitting the Source button as needed. Thing is I was saving wear and tear on the antenna, which I use a lot when I get to the woods on AM, by mostly using other sources around town. Oh well.

What I can't figure out is how it seemed like it was a short the first it happened going down the road, but now it just happens randomly at start-up. I would think almost like it might be that the two symptoms are for different fails. Weird.

Anyway, last bump in case anyone's back from the holidays who might have an idea.

 

[Hoosier Daddy]

Sounds like your head unit is going south to me. What's the background info on the head unit?

 

[greentruck]

The head unit is a Kenwood KPC-MP435U. Nothing fancy, but far from bargain basement. It was in my Isuzu Rodeo for the last year or so I owned it, then I swapped it into the 80 after I bought it (so just over 3 years in service.) Not a bit of trouble with it before this. Nothing else wrong AFAIK.

I have it wired through the stock amp. Everyone says the stock amp is cr@p, but my old abused ears don't notice. I dropped $100 on new Pioneer speakers recently for the doors, but only swapped them out, didn't touch the dash, so doubt that's relevant although this was a couple of weeks before the problem started with the antenna.

 

[ppc]

Get the stock amp out of the picture. Good chance that is your problem. The other choice would be to drive the antenna with a external relay.

 

[greentruck]

Phil,
I pulled out the manuals to see how the amp might figure in this, as I hadn't consider that as a possibility. The "motor antenna control relay" must see juice on the ACC circuit and that circuit does pass through the amp on it's way to the antenna ECU (not sure if the relay's in there or is separate).

Looking at things, it looks like I could just jump a wire for the ACC around the amp and onto the wire going to the relay. I'm really don't want to have to move anything else I don't have to.

Is there any way to confirm the amp is the issue? Heck, it might just be easiest to get another stock amp and keep things plug and play? Should be plenty of them around.

 

[Hoosier Daddy]

Help me understand your line of thought.

The head unit is switching to Radio and the antenna goes up like it is supposed to, right? That sounds like a head unit problem, not antenna. Are you thinking that the antenna is causing the head unit to switch over to Radio mode? Or what am I missing?

Unplugging the amp is a 3 minute job, so why not give it a quick try and see what happens?

 

[ppc]

Phil,
I pulled out the manuals to see how the amp might figure in this, as I hadn't consider that as a possibility. The "motor antenna control relay" must see juice on the ACC circuit and that circuit does pass through the amp on it's way to the antenna ECU (not sure if the relay's in there or is separate).

Looking at things, it looks like I could just jump a wire for the ACC around the amp and onto the wire going to the relay. I'm really don't want to have to move anything else I don't have to.

Is there any way to confirm the amp is the issue? Heck, it might just be easiest to get another stock amp and keep things plug and play? Should be plenty of them around.

With an aftermarket head unit you are going to have to figure out how it was wired. Are there two control wires coming from the Kenwood head unit, one for remote amp triggering and another for antenna control? The stock OEM amp is a completely different animal as compared to an aftermarket amp in the way the inputs and outputs are wired. The OEM amp quality wise is a piece of crap.