Usually cause the power surge protect diode has been destroyed. That's it's job. Sometimes the reverse power problem will travel beyond the diode and burn up a trace on the solder side of the board.
Solder a bit of wire to bridge the burnt spot. Rosin core solder. Replace the diode using a suitable size / make of diode. Make a drawing of the location of the silver band on the diode. Called the cathode side. Usually on the board drawn as line, l next to a triangle -l< Scrap electronics should have some you can use. Diode is close to where the power is entering the radio by a largish capicator.
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It would help us diagnose this if you could share a photo or a wiring diagram of what you're trying.
crwdns2934271:0crwdnd2934271:0 Kyle Wiens crwdne2934271:0
I hook up my cobra 29 classic with a 3 prong in line fuse to my Volvo semi truck and it keeps blowing fuses the diode is just fine
crwdns2934271:0crwdnd2934271:0 Adam Post crwdne2934271:0