Do you have any LED lights? These can make a lot of radio frequency interference.
I found the original antenna connector that plugs into the stereo backside, to be poorly crimped and falling apart. It was an intermittent issue until I replaced the original antenna after I Snapped it off.
I'd also found the original antenna ground on the underside of the quarterpanel to look like someone covered it with superglue and baking soda. it gets its ground from there and it was gettnig a poor ground on mine.
As an experiment, try putting a wire from base of antenna to known grounded metal or the battery -, or perhaps even the ground below the van itself.
Could be the FM tuner in the radio smoked itself too.
Thanks for the suggestions!
I suspect that the tuner is smoked... it is 20+ yrs old. I will check out the ground on the antenna though.
Strangely, the "extra" radio that is for the rear and part of the customization works just fine. Does it use the same or a different antenna? (anyone know?)