Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, bear with us; re-confirm and post back with the complete model number Uniden. Would this be a PRO520XL ?
Still, have you tried with:
Disconnect the PL-259 connector. In its place and for test purposes, carefully insert a length of wire to serve as test antenna (preferably 9' long). Determine if the S/RF would show incoming signals. DO NOT TX / press PTT.
The above would determine if it is internal to the Uniden or an antenna issue.
Loosen fully the outer/threaded part of the PL-259. Slightly pull back so that (only) the center/male part of the PL-259 is in contact with the middle portion of the antenna connector.
Might not be as effective as just a length of wire but, it should receive near / strong signals.
Negative, no TX. This is a test for the receive part only as above "...receive no transmissions..."
And how many volts is the truck please?
Is the CD directly wired to a 12V battery?
Consider making another ground connection to the metal body of the truck from the rear/body of the CB radio.
Also, please provide a clear picture of the "... plastic washer...between the antenna and the base..." Click HERE.
Normally should not cause a change in the SWR as it is meant more for mechanical function rather an electrical. It ensures that the antenna is lock tight to the magnetic base with no free play just like a lock washer.
...hence my request for pictures.
The "...plugged into the cigarette lighter..." would account for the "...lot of engine interference..."
Consider the earlier suggestion of hardwiring a ground strap from the rear of the Uniden (preferably a screw near the antenna connector) to a close metal part, bracket / part of the truck's body. This would serve to improve the ground plane (virtual RF ground).
Is the bottom /whip holder threaded all the way down?
Apologies; Internet was sluggish if at all.
Yes please for test purposes; K30 -> magnetic mount -> coaxial cable -> PL259 (male only) -> CB's antenna connector (center hole only).
The radio should be receiving:
Others to consider are noise filter similar to the product shown HERE (not as an alternate to the direct battery connection but) for further help.
Still, great! Good to hear that the issue has been resolved, congratulations.
Sorry but my participation is strictly limited to technical, repair and/or installation issues.
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