Antenna diagnosis... before I waste more time...

[cphilip]

A little help please.

Here is the situation as I found it. The PO has put in some sort of cheapish radio cassette. The original radio long gone. He has attached the keyed hot wire from the bundle under the HVAC controls and run aftermarket Speakers. Said the antenna worked for a while. And he didn't know why it was not working now. I don't see a constant hot to this radio nor is it the type that needs one. No storage or memory devices.

So I pop it out today and find that the blue wire (antenna signal has come out of where he had it and I know this because his connector was still in the plug but blue wire hanging loose).

So I say "AH HA"... could it be this easy?" well... um... no... I plug that back in and nothing changes really. No up nor down.

So I take out my Volt meter and I go to checking. There is a Two Wire Black plug there, appears old original plug he has the Blue wire into and I replaced into. Appears the old original power to radio? Anyway the left wire (the one not containing the blue wire) shows reverse polarity I think (not an electrician). By that I mean when I stick the Positive probe from my Volt Meter (set on DC 25V) and ground my Black probe I get a slight depression of the meter needle. Not a rise. Then when I reverse that, Poss + to ground and Neg - to the wire I get 12V!

Now is that supposed to be? So I go further and start testing the pins back at the Antenna and find two that give me the same thing! And no combination that gives me the opposite. Switch appears in proper orientation.

I take the radio out and open it up and clean it and take my 12V power supply and jump the two motor wires and I get motor spin. I see absolutely no burned up places nor wires lose or anything wrong with it. I clean it all with Electrical contact cleaner and re-grease the cam and put it all back together and after reinstall I plug it back in and I hear motor spin. I think then I got it.

I go up and turn key on and radio on and nothing. No up nor down even when I place it one way or another.

I take switch out and check continuity but I got no idea which pins should bridge in what position.

What is going on here? And what polarity is this thing in normal state?

Two wire plug normal for original radio plug. Reading reverse like a negative ground or something? Is something else supposed to be hooked up to function this thing? I know the blue wire is but is that the right place. Appears it is as putting it in the other of the two wires in the plug blows the radio fuse.

Not finding any other fuses blown and even replaced some that looked suspicious. Don't find a Fuse position listed on the fuse box cover specific for the Antenna either.

Help!!!!

1983 300D with probably original antenna and console switch.

[cphilip]

Ok... I am about to come to the conclusion that something from the original radio sent or changed the signal to the wire that is giving me Negative polarity (12V - ) now to somehow send a Positive signal to the Antenna for it to raise or that (more likely) this wire should not be giving me 12 V Negative and really should be 12V positive. Since the switch doesn't seem to do it and change that.... the Antenna seems to be getting a 12V neg feed but no signal to lower or raise it. It stays static.

So what could be constantly sending a 12 V Negative signal? Switch? Because the car is 12V Positive and the incoming power should be 12V + too as it all works off the same fuse. It could be that this wire comes from the switch? And the wrong signal is now coming from there? Since I don't have a wiring diagram I don't know.

Also complicating this is the fact that there is a circuit board in the Antenna that does some things I don't know exactly what they do. Its not as simple as just reversing polarity by wires which would be fairly simple to diagnose. I lose it when it gets into that board. Again... no logic diagram for that.

Is something supposed to be giving signal to this other wire? Not the radio on signal as it must sit in the other wire because attempting to put it into this 12 Neg wire blows its fuse. But that might be telling me something I don't know about the condition of the Antenna or Switch. What? ... I don't know. The problem is that I do not know what this other of the two wires does nor what its output should be. I know what it is now and that is a 12V Negative. If its supposed to be 12V positive then I could understand the set up... but I don't know what to be the case.