This is a pretty straight-forward fix and thankfully anyone can do FOR THE DRIVER'S SIDE FENDER INDICATOR, the passenger side I have not looked at but I assume it should be the same. Not sure if this will apply to the earlier model trucks (1976-1979) but for the later ones (1980-1983) this should work. Wish I took some pictures but my phone and camera needed to charge, and I'm tired so I'll describe how to do it and a word of caution. Some pictures for advice on replacing will be provided tomorrow! In my case, the way my indicator broke at such a way the front screw (the screw at the front-most section of the vehicle) and screw mount are no longer straight; anyhow here's how its done:

EQUIPMENT NEEDED:
Phillips Head Screwdriver of a small variety
Pliers (If you choose to remove & replace your plastic screw mounts)
Some time to kill

PROCEDURE:
1. Disconnect your battery!
2. Remove the lens (orange piece), bulb housing gasket (black piece), and screws [Plastic Screw mounts are up to you; I chose not too since my original ones are still good and I do not want to mess around with 40 year old plastic!]
3. Disconnect the female plug by gently prying up on the male plug's hold-down clip and pull it out
*3a. Clean the plugs if there is any dirt/foreign material/corrosion in them!*
4. Insert the new male plug into the female plug **[NOTE: From what I've seen, the prongs for both the male plug and bulb contacts are not too securely held in in the plug and bulb housing respectfully; when reconnecting a bulb or plugging it in, hold the wires when you're reconnecting anything! If not, you may only connect a single prong into the plug or bulb and have an improper connection!]**
5. If you have reconnected your plug and bulb and associated contacts/prongs successfully via reconnecting the battery and checking if the fender indicator turns on, re-assemble the light as you took it apart (gasket -> light housing -> screws, voila!)

If for whatever reason your DRIVER'S SIDE wire breaks/needs servicing, it is routed through the fender onto the other side next to the washer fluid/coolant reservoirs into a wiring harness.
Hope this helps!
-89p'up

 

Meant '83, darn brain keeps defaulting to '89 since I've had my Van longer than my truck right now!