I installed an old cobra 19 ultra in my ranger, with a magnetic antenna in the center of the roof. The wiring is all good and dandy but I went to calibrate the antenna and it's in the red, way above 3 on both 1 and 40. I have since disconnected power so I don't fry it but I don't know how to fix this. I've seen that I should extend the antenna. I've also read that I should shorten it. Can someone please help?
First, make sure your mount is getting good ground (this is why I don't like magnet mounts and why my Wilson 1000 is roof mounted). Bad connections/grounds (magnet not on enough metal, bad cable, etc.) will do that. Given how high your SWR is, I'd look there first. If that's good, then continue:
If this is a new antenna, depending on what type it is (C40? Wilson 1000/5000? Cobra "celluar style?), you may need to go shorter right off the bat; they are sold long as it is obviously easier to shorten an antenna rather than make it longer (just cut it with bolt cutters in 1/4" increments until it's there). IIRC wilson whips are sold that way (at least the short load that I have in mine).
Side note- speaking of short load whips, these need to be adjusted above the center element; adjusting the section below such can and will cause headaches. As will installing one upside down; the length of the whip section going to the base and possibly orientation of the element relative to the
base is important and pre-designed and made to the correct length.
Here's the trick (and why one should use a meter, not a cal light): you need to test it right in the middle (20) and see if it gets better at all going up or down. If its better going up from there, you need to go longer, if going down helps (quit laughing, you 2nd grader!), you need to shorten the antenna. Then, adjust until tuned.
Hope this helps. (FWIW, I'm an EET who both does CB (eventually Ham) and also took a couple of college classes in this sort of thing).