I've got an 87 Toyota pickup and the stock radio and speakers don't work. before I spend some money and upgrade the radio and speakers how do I diagnosis the actual wiring harness to make sure it's not the problem???

 

has the harness been messed with at all?

 

Make sure you have voltage to the receiver. If you have power at the receiver that means that the problem is signal related. It is either your signal at the receiver or your speakers at that point. Replace one or the other maybe by borrowing one before you have to buy one.