I messed up my OE power antenna (bent mast badly). Found a replacement on ebay. Looked perfect right number of sections, harada, same wire colors and bullet connectors to fit my 75. Works fine when powered up with outside source BUT does not use a center tap motor, so you have to reverse the polarity of the wires for up and down, there is NO center tap ground section. The stock radio up down is a SPDT sending B+ to one wire at a time, B- is thru the chassis ground. 

So it seems like the only solution is TWO SPDT (or more commonly avail DPDT) 12v relays. Each coil will get Ground and one of the existing wires from the harness so each relay will work independently of each other, depending on the up or down of the antenna switch. With that it should be simple run both a B+ and B- thru each of the switched sections of the relays, then connect up the antenna motor to both, one reversed from the other. Unless a relay gets stuck it seems this would work out fine. I dont know if there is such a thing as a dual coil relay that I could configure like a DPDT switch with a center off, like an old DPDT knife switch I used to mess with doing this reversal thing (in that case the antenna motor goes to the center off, then reverses power is provided to the two poles, pulling the center to one side or the other reverses the center polarity).  

maybe a solid state fix

 

came up with this

 

That circuit looks OK to me.

Have you considered using a microprocessor and pulse width modulated outputs instead of relays? Or little CAN bus receivers?

Or just go cheap with a DPDT switch...Yeah, I know. That's no fun.

1 hour ago, Captain Obvious said:

That circuit looks OK to me.

Have you considered using a microprocessor and pulse width modulated outputs instead of relays? Or little CAN bus receivers?

too many episodes of battle star galactica for me to do that.

1 hour ago, SteveJ said:

Or just go cheap with a DPDT switch...Yeah, I know. That's no fun.

Trying to stay with the OE installed antenna switch (SPDT center off). The antenna came with a pre wired center off DPDT X configured switch.

It took a while, but I found the relay that I removed from a parts car that had the same type of antenna. It is a simple single coil double set of contacts style relay.Here is how it was done. In the de- energized state the power comes in on the red and out on the green, ground is blue to jumper to top terminal on left contact, yellow has no connection . In the energized state the power comes in on the red and now comes out on the blue and the jumper to the top terminal on the left contact has no connection, yellow is ground and green has no connection. I did not look at it when it was wired up, but I think if you wire your “up” on the green after the relay and use the “down” to energize the relay it should work.The blue goes to one wire on the motor and the yellow and green go to the other wire.

Edited October 26, 20222 yr by 240dkw

roger that, I think my previous had an issue with the motor back feeding one of the coils anyway, making it a random event on which way it would go. Not sure but I like this setup better thanks for posting

 

the single DPDT relay did the trick. wired up 240dkw described, works great. I deleted the old video to avoid anyone following in my foot steps. will post a revised later.

video

 

last one

 

Edited October 26, 20222 yr by Dave WM