I have a '66 F-100, we didn't drive the vehicle for several months, then the battery stopped holding a charge, once we jumped it the truck would be fine, but overnight the battery would drain. Recently the headlights were working intermittently. Then the alternator light came on. There were some loose connections at the alternator, and it was really old... I replaced the alt. The headlights still don't work, and the alt light is still on. What can I check? How can I check it?

Thanks,
Josh

 

Check the fire wall connections for a good contact and then make sure to put some dielectric grease on them. I found my bad connection after replacing half of the wiring in the engine compartment not to mention the battery and voltage regulator. Just a good place to start. Then after that maybe check the fuse block connection on the head light switch if your is like that. Mine has the fuse block clipped to the bottom of the head light switch.

 

Josh! Welcome to FTE! Most parts stores will test the alternator and regulator for you. They will test the battery as well. The starting point for this is a good fully charges battery. There is a device called a fuseable link between the battery and alternator. It us usually blue and looks like a fat wire. It will have a small square rubber tab on it. Most likely this is burned (it is supposed to) like a fuse. There are two flavors of voltage regulator, use the small flat silver one, it is an integrated circuit and is better than the old mechanical type. Battery cables should be replaced as well as the starter relay to starter cable. After this follow Air Harley's advice and clean and lube all the bulk head connectors. There is a better solution IMHO! I use a one wire GM alternator and toss the Ford wiring harness, alternator and regulator. I'll e-mail the instructions if you are interested.

 

William I would like to see those directions. Thanks for your help. Would that fusible link be the culprit in making the headlights not work?


Josh

 

Josh, The fuseable link disconnects the alternator and then the battery goes dead so in a way it will affect the lights. To trouble shoot any of this you must have a fully charged battery, good connections on all the cables and plug in connectors. Here are the instructions.
INSTRUCTIONS: What follows is a step by step installation process along with parts and tool requirements. Ford used two mount locations for alternators and generators on FE engines, one at cylinder head level, the other about 8 inches lower. I chose to use the lower location. Firstly the large 85 amp alternator didn't fit in the upper location (it is too long), and the upper location is to close to heat generating sources (against the head and above the exhaust manifold). The lower location is cooler. Delco alternators run a little hot anyway so I wanted to install it where it would be as cool as possible. Lastly, the lower location looks cleaner and provides a less cluttered appearance. The smaller 45 amp Delco alternator will fit easily on the upper location. The wiring connections are the same.
IMPORTANT NOTE: The pivoting mounting bolt for the Ford Alternator is 7/16 inches in diameter, the Delco is 1/2 inch. This necessitates drilling out the alternator mounting bolt hole to accept the larger 7/16 inch bolt. I performed this operation by putting the alternator in a vice and carefully running a 7/16 inch bit through the pivot bolt hole.
PARTS:
85 Amp Delco Alternator purchased without core at Napa for $91.00
42 inch fan belt purchased at Napa for $6.95
Delco GM alternator connector plug purchased at Napa for $6.89
Some red 10 gauge primary wire
Some green 18 gauge wire
GM Battery cable with extra 10 gage wire installed
Heat shrink
Aluminum alternator pivot bolt spacer with a 7/16 inch hole. The original steel spacer and some flat washers will also work
Miscellaneous solder less electrical connectors, wire ties and flexible wire cover
Lower mounting bracket from a 66 Galaxy with a 390
Late sixties/early seventies F100's with a 390 or 360 motor are also a good source for these brackets
TOOLS;
A small hand grinder to work on the engine block cast flashing and to grind a little off the alternator adjusting arm for clearance at the vibration damper.
Wire cutter.
Wire crimper.
3/8 drive socket set
REMOVE:
Place a piece of cardboard between the fan and radiator to protect the radiator from loose parts and wrenches. Pull the battery, positive battery cable, alternator, alternator to regulator wiring harness and the voltage regulator. Near the regulator is a connector with a 18 gage green wire with brown stripe paired with a yellow16 gage wire. The green/brown wire will connect to the alternator and operates the ALT light in the instrument cluster. I cut the Ford plug off and install a Weather Pack Connector on the green/brown wire. The yellow wire operates the horn and it is hot with the ignition on.
Loosen and remove accessory drive belts. Remove the fan and water pump pulley. Take off all the original alternator mount brackets and clean the area you will be working in. Now is a good time to grind off any cast flashing from the engine block near the timing chain cover and on the corner of the block below the exhaust manifold. Doing this will provide a little extra movement of the alternator when you install the belt and it makes things neater. Run a tap in threaded holes and use a little air or WD 40 to clean any debris out of these holes.
MECHANICAL INSTALL:
The mounting bracket, alternator, pivot bolt, spacer and the adjusting arm. The adjusting arm may require some grinding to provide clearance between it and the vibration damper. Use a bolt with metric thread to fasten the adjusting arm to the alternator and just for good measure put a nut on the end where it threads through the alternator. Trial fit everything, tighten the mounting bolts finger tight until you are sure everything fits nicely without binding. The alternator drive belt must ride straight over the alternator pulley, the water pump pulley and the vibration damper pulley. Use wire ties and a flexible wire cover for the wires and harness you built.
WIRING DIAGRAM:
Install a red 10 gauge wire with a crimp on ring connector from the battery post terminal on the alternator to the positive post on the battery. I used a new red GM Positive battery cable with an extra attached 10 gage wire. A 10 gage wire from the battery post terminal on the alternator to the positive battery cable side of the starter relay will also work. It's just that the GM battery cable has this extra wire and makes for a neater installation. I shortened the GM battery cable and soldered on a new end connector. Get a metric nut to attach the ring connector to the battery post on the alternator. I think next time I'll just run a 10 gage wire from the alternator battery post over to the starter relay.
The Delco GM alternator connector is keyed to fit and will only plug into the alternator one way (the right way). It has two 18 gage leads, a white one (blue on the wiring diagram), with solder less crimp connector installed and a red lead about three inches long with a ring connector. The red wire with ring connector connects to the battery post on the alternator, (same post as the 10 gage wire running to the positive battery post). The other wire (mine is white), connects to the ALT light. From the white lead on the alternator plug in connector, run a 18 gage wire under the battery box, up and across the radiator core support and crimp connect it to the 18 gage green with brown stripe alternator charging lamp indicator wire from the bulkhead connector. This circuit operates the alternator charging lamp indicator. The alternator will work fine with out the charging lamp connected. I prefer to connect this circuit and use an ALT light. The green wire with brown stripe is paired with an 18 gage yellow wire that connects to the horn relay. The yellow wire on the alternator diagram is not used in this application.
TEST: Turn on the key, the ALT light should come on. Start the engine, the ALT light goes out. Measure alternator voltage output, across the battery posts. The reading should be 13.5 to 14.5 volts with the engine running at idle. The same reading should be 12 volts with the engine off.
ACKNOWLEDGEMENTS:
Trail Rider, for advice and the wiring schematic.
Sparky, for lots of really good electrical information.
Use a keyed plug in connector for terminal one and two.
Yellow lead is not used.
Red lead (BATT) connects to the positive battery post.
Blue connects to the ALT light (green with brown stripe) on 66 F100s.

 

William thanks for that it is very detailed.

I believe i have found my immediate problem. The connector on the firewall closest to the fender is bad. It is corroded and the male plug coming from the cab is broken off in the female end of the engine compartment plug.

Do you have any idea where i can get a replacement plug? Can I replace just the plug or will I have to replace the whole wiring harness run?
Well, thanks again!

Josh

 

Most eletrical supply stores carry the connectors you need, if not try Radio Shack. Just cut the old on out and take it with you to match it to a new one.