Classic Car Woes, 1965 Buick Skylark

I'm doing an install for a customer with an old 1965 Buick Skylark. Doing a new single din with a brick amp & mounting speakers under the dash. He wants to keep the old AM radio in the dash operational, so I'm hooking up both radios to a switch so he can switch between them. The only problem is I'm not sure what to do for the new radio's antenna. The factory antenna is hardwired into the old AM radio. My thought was to splice an adapter end into the factory wire so both radios could share the antenna.. I did some searching and this is a pretty specific situation so not a lot has come up. First time doing an old classic car like this. Just trying to see if anyone has tried to do something like this or if anyone foresees any issues with my idea. (My only thought would be to splice I'd have to break the shielding, I dunno.) Thanks.

Here's a potential solution from a company I worked with back in the 80s that specializes in audio for classic vehicles. https://customautosoundmfg.com/product/accessories/hideaway-antenna the12volt • Support the12volt.com

The original antenna end should plug into the back of the factory radio. It might be stuck in there so be careful pulling it out. It should be a standard for the time, Motorola end. One could try an antenna "Y" splitter with the factory antenna lead going into the one part of the Y and then one other end of the Y plugging back into the factory radio and the last part of the Y going into the aftermarket radio. What you are asking about switching reminds me of the days back in the 70's with adding a stand alone cassette player to a factory am or am/fm radio and one could go old school with a multipin slide switch or one could get a multipin relay to where when the new radio is turned on a relay throws over the speaker setup to the new radio and then when switched off connects the factory am radio to the speaker(s). Just a heads up but watch what get's hooked to the original am radio. Chances are it has to be an 8 ohm speaker. https://vetco.net/products/car-radio-antenna-motorola-connector-splitter-cable-1xf-2xm?gclid=Cj0KCQiAz53vBRCpARIsAPPsz8UeMHlS8zOv_gPLKKUutR9AGLfgH1hGglbMUv6t1JJU3o4dFEU7FNwaAk0mEALw_wcB Jim1968 Chevy II Nova Garage Find 2012

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I too am thinking the antenna is stuck in the socket. I have never seen a vehicle with a hardwired antenna. Wd-40 could be your friend.

I appreciate the input guys. I'll have to check back there again, fingers must have lied to me. Going to order a Y-splitter like was mentioned above.