The truck is a 1981 but you are missing a digit in the seriial #. There should be 6 numbers.

in the yale model coding system it goes like this

GLP030UAB085P

GL = Fuel Type LP
P = Tire Type Pneumatic
030 = Rated Capacity 3000lb
The group of letters after the capacity can vary depending on machine Designation, design series, manufacturing source, engine model, transmission and mast type.
U = Special Designation (engine type mazda? probably a UA?)
A = Design Series
B = Transmission Type (automatic 2 speed?)

085 = mast height in inches (collapsed)
P = ? year of mfg?

This was before yale started using thier new serial numbering system which they moved the year of mfg designation into the serial numbering in which the end letter on the serial number would be the year of mfg.

Also from looking at the serial number this lift is definitely old , I'd say built probably back in the late 80's early 90's. Someone else may be able to narrow this down better that has more familiarity with their model nomenclature.

As for this tank on the side.. can you elaborate in more detail what you mean? Is this tank part of the frame?(which in this case would be the fuel tank), or is it a component inside the engine compartment? Need more clarity on this part.

That explains a lot. Thanks for your help.

Mazda VA engine and probably a early '80s model year. Yes, GLP, the P means pneumatic tires, 030 means 3000 lbs. capacity, AB is the model number, 85 is how tall it is in inches in the lowered position.

any idea on the year? From what I have been able to find out, I think it is a mitsubishi engine? I'm guessing the GLP would mean gas or LP, the 030 means the 3000lbs limit, not sure what the uab085p means. somewhere it should tell me the year?

Sounds like the gas tank and the wire is to the fuel level sensor. Some of those machines were duel fuel, LP or gasoline. If yours is just LP then it's not used.