Ford doesn`t have a lock on better ideas. Chrysler came up with one of its own-transforming the Dodge Dakota pickup truck into a convertible.

Weird? To be sure. Fun? No doubt about it.

We`ve always enjoyed the midsize Dakota truck. It`s larger, roomier and can handle more cargo than a compact Ford Ranger or Chevy S-10. Yet it`s smaller than a full-size Ford F-series or Chevrolet C/K pickup and therefore more fuel efficient and more manageable in such situations as backing into that one vacant parking spot.

But a convertible top adds a new dimension. If the truck owner can expose the cargo in the rear bed, why not expose his or her dome in the passenger compartment.

We test drove the Dakota truck and, despite temperatures in the mid-40s, we set out to remove the canvass and enjoy a fall cruise.

The top is easily removed. Lower the side windows, open the snaps above the sun visors and grab the top and lower it onto the bed in back of the driver`s seat. But beware the roll bar over driver and passenger head when lowering the top so you don`t bang it with your forearm.

The top rests against the rear truck bed and doesn`t fold down into it. So you have to ensure there`s no cargo in back that the top might hit and damage the plastic window or rip the canvass covering.

A boot covers the top to keep it fashionable. The problem is that the boot fits in a large duffle bag and finding room to store the bag in the passenger compartment is a chore. The top also can be completely removed.

It would be nice if Chrysler came up with a removable hardtop cover over the canvas so you`d have a choice of soft or hardtop motoring as in the TC by Maserati. Such a top was considered but the idea was shelved for 1990 based on cost. A removable hardtop is back under study for 1991, providing Chrysler can get the cost down.

Once the top was down, we followed the standard operating procedure for drivinga convertible when the temperature is in the mid-40s. We pushed the heater lever to the farthest most point in red, turned the fan to high and took off.

Odd how fellow motorists took to the experience. Several of them must have been colder than we were because so many glanced at us and started shaking their heads from side to side. A couple walking huddled together along the lakefront in thin sweaters whose complexions were taking on the same hue as the water giggled at the fool in the ragtop truck with the top down.

Luckily the 3.9-liter V-6 that powered the truck was performing at optimum and after a few laps away from Tribune Tower it quickly brought us back. Fun and invigorating, but we don`t recommend a convertible test drive when it`s that chilly and the wind`s blowing in off the lake.

The vehicle carries a few words of caution. Don`t lower the top when the temperature is below 41 degrees or you risk cracking the plastic. And the manual warns not to visit an automatic car wash, risking damage to the top and window.

We experienced only one annoyance. Because the convertible top rests against the rear bed sides, it doesn`t lower flat. Part of the top sticks up and interferes with rear vision in the mirror. You have to use the side mirrors for optimum vision.

The Dakota truck offers a convertible version in the base two-wheel-drive model starting at $13,345, in upgraded two-wheel-drive Sport version for $15,500 and in the four-wheel-drive Sport version we drove starting at $17,650.

Standard equipment in the four-wheel-drive Sport includes the 3.9-liter V-6teamed with a 5-speed manual, power brakes and steering, power windows and door locks, tinted glass, dual remote mirrors, sports styled steel wheels, AM- FM stereo with cassette and clock and leather wrapped steering wheel.

A 4-speed automatic transmission runs $819; air conditioning, $804; a 22- gallon fuel tank, upgraded from the st ndard 15 gallons, runs $53; and upgraded radio, $125.

>> Dakota 4WD Sport ragtop
Wheelbase: 112 inches Length: 185.9 inches Engine:3.9 liter, 125 h.p., V-6 Transmission: 5-speed manual; 4-speed automatic optional Fuel economy: 15/19 m.p.g. manual; 15/20 m.p.g. automatic Base price: $17,650 Strong point: Top down motoring in a truck Weak point: Rear visibility because the top doesn`t fold into the cargo bed >>