Over the years I've had about everything that could fail did on my 1990 Cab top many different times. It looks like your '88 is similar with a couple difference such as the location of the top control unit. But if you say that the lift motors work and only the lock motors don't I would first suggest you check all four micro switches. Yes there is 4 and the system requires all to be working. Look at this video I found on the internet that shows the control unit and checking the micro switch tests.
https://www.youtube.com/watch?v=jhrBzyk0LiY . Usually I found that the front top switch trip mechanism wire broke not the switch. If it's this let me know and I can tell you how I fixed mine or I may have a spare I might sell you but I will have to check if i still have one. Second it could be the lock motor gear box that plastic gears could be broken and jammed. URO has a brass steel replacement set for them. Easy to fix. Look at this video I found on the internet that shows its repair.
https://www.youtube.com/watch?v=VMnGfM3I-Xw Third it could be the control box with failed solder joints. Not so easy to re-flow the joints. Really need a qualified solderer. Currently I have mine set simi-mechanical using only the lock motors after lifting the top by hand. Much faster then using lifting motors. All still works if I want to put it back full automatic. At one point until I found out how to repair the controller I had a electrician friend wire in switches to control power to the lock motors. I since then removed them after I found the real problem.
Not to worry about opening it to test. You can always close it again mechanical if even the lift motors stop working too. Just loosen the center bolt on each side of both the rear side gearboxes and lift it by hand then use the screw driver to turn the lock motors to close.