Speaker question
 

Perhaps a dumb question, but can I use the same speakers for two systems? I’d like to I install a dual cone ( 2 channels ) speaker in the dash of my 72 to facilitate an underdash 8 track player. Can I use one of the channels to serve my factory Am radio ? Maybe use diodes on the to prevent back feed?

Re: Speaker question
 

I believe you can't easily use the same speakers for 2 systems. From what I've read the factory radio requires an 8 to 10 ohm speaker and you would best not deviate from that because you can supposedly burn out the radio's amp. It would be easiest to put stereo speakers under the seat and use those for the 8-track, and leave the AM radio and its speaker alone.

But, an idea would be to energize a relay or relays from the 8-track player coming on, and the relays disconnect power from the AM radio and connects the stereo speakers separately to the stereo outputs of the 8-track player. With the 8-track player off and relays de-energized, the radio gets power and speakers get connected in series to the AM radio output. Alter the 8-track player to tap into it's on-off switch to power the relays, and locate the relays under the dash somewhere.

Re: Speaker question
 

Yeah, my thought was similar. A single throw, double pole Toggle switch (basically a three-way ) under the dash, With 6 diodes on the speaker outputs, 4 on the eight track and 2 on the am radio. Technically, only two on the eight track as it would only share one channel with the original mono radio. If it works, it would far cheaper and easier than a separate set of speakers installed somewhere else.

I guess as your train of thought would be, I could tap the load side of the radio’s on/off switch to control a small ice cube relay to control the power to the eight track. Would still need the diodes to prevent increasing the speaker resistance load.

Re: Speaker question
 

No diodes, use relays that you can cleanly and completely connect/disconnect from the player or radio. Speaker signals are AC current, not DC such that you can direct with diodes.
Regarding power, my thought is to cut power to the AM radio when the relays give the speaker to the 8-track player, because you are not supposed to power up the AM radio without speaker attached.
It would probably take several relays because when connected to the AM radio the speakers should be connected in series with each other to add up the impedances (4 + 4 =8 ohms) that the AM radio needs.