I've heard of a way of using two jumper cables (wires with alligator clips on each end) to enable the computer and reset the light with 2 taps on the connector where a code reader goes. I would not trust that.
The way I solved the problem was to get a code reader from Auto Xray (www.autoxray.com). I bought mine on sale at Kragen Auto, so I know they are available in that kind of store. The cost of mine was about $200.00 which is steep for just re-setting a light. It is a very nice tool to have if you do a lot of work on your vehicle. Mine came with adaptors for all the domestic and foreign interfaces, so it is a very good tool for the serious hobbyist or week-end mechanic.
The third way is to take the vehicle to AutoZone, if you have one locally. I hear they will loan you a reader which can be used to reset the light, or they will do it for you. You might want to ask around.
The fourth option is to drive around with the light on. I've been known to do that for times too. Not the best solution to the problem.
By the way, to just read the codes, you can use the ignition switch and the check engine light. From a complete off position, cycle the ignition switch through on and off 5 complete times. Then count the number of blinks you get. You will get a group, a pause, then another group. count the first group, then the second group. If you get 5 blinks, pause, and 5 blinks, that is 5 5, and means there are no errors stored.
Best of success with your truck. My 1989 is still on the road very nicely, and I'm sure yours can be too.
Rick/
MY 1988 has a small blue box locate just above the emergency brake you will have to remove the lower cover on the dash inside the blue box you can just see a small white button i used a small probe to push it in and the maint light goes off. P.s. the truck was running at the time i reset .