See Figures 1, 2, 3 and 4
There is only one fusible link used on all 1972-86 pickups (620 and 720D series) and that is the thinner of the two wires connected to the positive battery terminal. On 1986-88 D21D series trucks there is also a brown one used in the headlight circuit, brown one used in the ignition switch, green one used in the power windows, brown one used in the EFI control unit and a brown one used with the EFI injector. Replacements are simply plugged into the connectors in this wire.
1970-71 trucks (521 series) do not have a fusible link.
The fuse link is a short length of special, Hypalon (high temperature) insulated wire, integral with the engine compartment wiring harness and should not be confused with standard wire. It is several wire gauges smaller than the circuit which protects. Under no circumstances should a fuse link replacement repair be made using a length of standard wire out from bulk stock or from another wiring harness.
To repair any blown fuse link use the following procedure:
- Determine which circuit is damaged, its location and the cause of the open fuse link. If the damaged fuse link is one of three fed by a common No. 10 or 12 gauge feed wire, determine the specific affected circuit.
- Disconnect the negative battery cable.
- Cut the damaged fuse link from the wiring harness and discard it. If the fuse link is one of three circuits fed by a single feed wire, cut it out of the harness at each splice end and discard it.
- Identify and procure the proper fuse link and butt connectors for attaching the fuse link to the harness.
To repair any fuse link in a 3-link ground with one feed:
- After cutting the open link out of the harness, cut each of the remaining undamaged fuse links closed to the feed wire weld.
- Strip approximately 1 / 2 in. of insulation from the detached ends of the two good fuse links. Then insert two wire ends into one end of a butt connector and carefully push one strip end of the replacement fuse link into the same end of the butt connector and crimp all three firmly together. Care must be taken when fitting the three fuse links into the butt connector as the internal diameter is a snug fit for three wires. Make sure to use a proper crimping tool. Pliers, side cutters, etc., will not apply the proper crimp to retain the wires and withstand a pull test.
- After crimping the butt connector to the three fuse links, cut the weld portion from the feed wire and strip approximately 1 / 2 inch of insulation from the end cut. Insert the stripped end into the open end of the butt connector and crimp very firmly.
- To attach the remaining end of the replacement fuse link, strip approximately 1 / 2 in. of insulation from the wire end of the circuit from which the blown fuse link was removed, and firmly crimp a butt connector or equivalent to the stripped wire. Then, insert the end of the replacement link into the other end of the butt connector and crimp firmly.
- Using resin core solder with a consistency of 60 percent tin and 40 percent lead, solder the connectors and the wires at the repairs and insulate with electrical tape.
- To replace any fuse link on a single circuit in a harness, cut out the damaged portion, strip approximately 1 / 2 in. of insulation from the two wire ends and attach the appropriate replacement fuse link to the stripped wire ends with two proper size butt connectors. Solder the connectors and wires and insulate with tape.
- To repair any fuse link which has an eyelet terminal on one end of such as the charging circuit, cut off the open fuse link behind the weld, strip approximately 1 / 2 in. of insulation from the cut end and attach the appropriate new eyelet fuse link to the cut stripped wire with an appropriate size butt connector. Solder the connectors and wires at the repair and insulate with tape.
- Connect the negative battery cable to the battery and test the system for proper operation.
Do not mistake a resistor wire for a fuse link. The resistor wire is generally longer and has print stating, resistor-don't cut or splice. When attaching a single No. 16, 17, 18, or 20 gauge fuse link to a heavy gauge wire, always double the stripped wire end of the fuse link before inserting and crimping it into the butt connector for positive wire retention.