Fusible link from the starter

Check fusible links.

BOTH ANSWERS ARE GOOD BUT THERE IS A FUSIBLE LINK WIRE ON THE STATER SOLINIOD THAT MAY BE BURNED OUT LOCATE THE FUSIBLE WIRE AND GIVE IT A LITTLE TUG, IF IT STRECHES IT IS BAD MAKE SURE YOU REPLACE IT WITH ONLY FUSIBLE LINK WIRE

Sounds like he caused a wiring short and blew maybe a fusible link. This was I think before maxi-fuses, so fusible links were used to distribute power from the battery.
You get nothing by turning the key to ON? No warning lights on the dash, no gauges, no starter action? If so, follow your positive battery cable to find the location of these fusible links. Sometimes connected to the cable at the starter motor, sometimes off a pigtail from the positive cable. Could be 4 or 5 links, one for lights, one or two for ignition switch, one for wipers, etc. When a link blows out, you just cut it out and replace with the same rated fusible link. A bad fusible link will show signs of having blown. The wire my be burned looking, or may have a rough feel, like bubbles in the wire insulation. What happens is the smaller gauge wire in the link has burned through and saved the wiring harness from burning up.

On the positive side of battery Julie is where your fusible links are,you say it's getting hot,I would follow all wires,look for burnt or swollen wires,they go to starter.Here's a wiring diagram,it shows that you have 3 fusible links leaving your positive battery,they need looking at,check all wiring in line with positive battery cable.Look at diagram number 25,enlarge to see.

Hi Julie.I have a 85 nissan truck too,it's silver,go to your positive battery cable,you have a fusible link tied in,about 5 wires,check them for burnt or swollen wires,won't start if burn't,here's a link to my fusible link,will be different than yours cause I changed mine a while back,the fusible link is 22.00 at dealer,can use same gauge wire to fix.Here's a video of my truck.

Sounds like a fusible link burned out. Check the wires at the battery cable post of the starter. The smaller wires connected here are the fusible links if equipped. If not then check where the smaller positive cable off the battery goes to the fuse box. It will be connected to fuses there which could be burned out.

The first thing to check, is that you didn't accidentally leave one or more of the fusible links off of the main power post of the starter.

Fusible Links

The engine compartment wiring harness has several fusible links. The same size wire with a special hypalon insulation must be used when replacing a fusible link.
The links are located in the following areas:

1. A molded splice at the starter solenoid Bat terminal, a 14 gauge red wire.
   
2. A 16 gauge red fusible link at the junction block to protect the unfused wiring of 12 gauge or larger wire. This link stops at the bulkhead connector.
   
3. The alternator warning light and field circuitry is protected by a 20 gauge red wire fusible link used in the battery feed to voltage regular #3 terminal. The link is installed as a molded splice in the circuit at the junction block.
   
4. The ammeter circuit is protected by two 20 gauge fusible links installed as molded splices in the circuit at the junction block and battery to starter circuit.
   

Other things it MIGHT be are the ignition switch, located on top of the steering column:


The other thing it MIGHT be is a faulty ignition cylinder (where your key goes into to start the K10).

Check the wire harness on the steering column also.

Turn the headlights on. Headlights don't come on? Bad Positive cable to the battery. Fusible link has blown. (Fusible links are in cables themselves. They usually resemble a rectangular flat spot in the cable. They can also be rounded. When you see them, you'll know that is it) There may be one or two cables coming from the starter, that are small Positive wires. Sometimes the blown fusible link melts through it's insulation, and the damage is obvious. Sometimes it's Not. Isn't wiring fun(?)

Going to sound like a dumb answer but try removing the spark plugs and then see if it turns, or if water comes out of any plug hole. disable your ignition so spark can't cause a fire. Then tell me what you find...