Radio/electric aerial not working!

[Ceejay 72]

Can any electrical geniuses out there help with this one?
The radio in my Mk 1 switches on and has a carrier wave, but the electric aerial is not working. I removed the backplate on the aerial to expose the connections and applied a multimeter. There are two input cables, brown and white. With the ignition on, there is no voltage across either terminal to earth (the brown actually shows -1 volt). With the radio then switched on, there is 11.5 volts to earth on the white terminal, but only 10.5 volts on the brown, falling steadily to below 5 volts if the connection is maintained.
As the earth connection I used was direct to chassis, not the aerial earth, it seems to me that this indicates a fault other than in the aerial itself, but I am totally mystified.
Any ideas?
Thanks,
Chris

[Phil S]

some electric aerials have a built in relay try an additional earth. you should have a constant live and a live when the radio is switched on. you could try jumping the constant live across so both have a constant live. if it still fails to operate its shot

[barkerwilliams]

On my aerial there is the earth connection and an always live feed, perhaps the brown on yours and a signal wire - perhaps your white. If the signal wire is earthed the aerial will lower, if the signal wire is +12v the aerial will raise. There is usually an internal limit switch that stops the motor top & bottom.

In my experience the aerial sections often bond together with either rust or filth and the motors lack the 'umph to raise / lower.

Alan

[trunt]

Maybe don’t do that yet, you would risk blowing the radio!

With the ignition on there should be 12v on one wire(brown?) from your description I would guess that a fuse for that supply is blown?

the 11v you get with radio on is probably the signal from the radio but without the supply it won’t work. Shorting it may overload the radio!

terry

[Ceejay 72]

Ah, it may be a little clearer, thanks! If the white is the signal wire, that would make sense. Perhaps I'll try a separate direct 12V feed to the brown terminal and see if the aerial raises. There appears to be a relay of some sort built into the aerial casing. Would it be possible to get the low and reducing voltage on the brown as a feedback through this?

[DZP]

Hi Chris,
It is quite a long time since I installed an electric aerial, but I think this is how most of them (with a built-in relay) work.
There should be 3 wires feeding the aerial.
Permanent 12v live: usually Red. This feed allows power to the aerial motor to extend and to continue to retract even when the radio (and or ignition) is switched off.
This is usually fed directly from the battery via a fuse, although I think sometimes fed from the ignition on relay.
Radio on: usually Blue or Green. This is the feed from the radio causing the aerial relay to switch motor direction and ultimately extend it.
Earth: usually Black. Connected to a chassis.
If you can find the name/manufacturer on the aerial, then I would try Googling it to find the wiring diagram.
I would work on the aerial completely separate to the car. e.g. disconnect it from the radio and even take it out of the car if you can.
Use a feed from the battery with a small amperage inline fuse.
From the information already supplied then it sounds like:-
Radio On = White
Brown = is probably connected across a capacitor somewhere and discharging through your meter, hence the diminishing voltage.
It could possibly be the negative side of the relay, but I would not expect that.
Logically it would be the "permanent 12v" feed, but I would prefer to be sure before directly feeding power to it.
It sounds like there is no separate earth wire for the aerial, so it will have to earth through physical connection with the chassis, which is never good, so are you sure it is earthing OK?
If you can see the internals of the aerial and can post a picture, I might be able to advise on how to wire it up.
Regards,
Dennis

[Ceejay 72]

Thanks Dennis, I'll see if I can find the manufacturer's name. There is black earth wire - I just didn't mention it.
I'm going to try to trace the white and brown cables back to the console, or wherever they terminate! I'll take a picture of the internal connections of the aerial too.
Regards,
Chris

[Ceejay 72]

No maker's name on the aerial, looks very like a "universal" one advertised on-line. Here's a picture of the electrical internals.

[DZP]

Hi Chris,
Yes there is a capacitor in there, that is the blue can next to the red wire.
I cannot quite see where all the wires go to and from
Do the White & Brown wires both go to the relay board?
Where do the 3 wires on the motor (on the left) go) e.g.Top, Middle, Lower connections? Do they all go to the relay board?
Are red and white connected together on the middle motor connection (on left).
I can see a set of contacts on the relay, that is probably a thermal cut-out so make sure the contacts are clean.
It is looking like this, but I am not sure yet.
Brown = Permanent live
White = Radion On
Black = Earth.