74 mercruiser 120hp trim issue

I have a 3 button dash control

I have a 3 button dash control and my trim will go down but not go up. When I bought it the guy told me it didnt work but he shorted something back by the engine to get it to come up (of course I wasn't watching close enough) and now I cant get it to trim UP and now it's all the way down. My gauge doesnt seem to be working either. My cylinders each have 2 hoses attached outside boat and I can physically move the the trim all the way up but then it drops back down under no resistance. Any advice or info on what to look for would be MUCH appreciated. Itching to get this boat in the water. Newbie in need

"David:

Do you understand D

"David:

Do you understand DC voltage circuitry used in boats? You will need a manual w/a wiring diagram and DVM or test light. The wiring in your boat is 35 yrs. old and most likely has numerous problem areas; corroded wires and connections, worn switches and solenoids, etc.

Test the switches for operation. Test the wires from them to their end points. Look for broken and corroded connnections. Use jumper wires to temp. replace a wire for testing."