I have been having some electrical problems with my 79 f150 lately. There are multiple problems so i figure ill tell ya everything i know about each and see what you guys think. I think i may know a few of the problems and will mess with it tomorrow after i get off work (messing with wiring in the dark is usually fun). 1st of all i replaced the lock cylinder in the ignition switch and the 2 door locks to be the same. I needed a new door lock so i got new locks for both doors and a lock barrel (not the whole ignition switch). The problem is that there seems to be an inbetween position between run and start on the switch. Sometimes it sticks between them and the cd player and heater/as will not run when it is like that but motor runs fine. I can jiggle it between the 2 positions and with my original it would do this. Also sometimes if i have to crank the motor for a little longer it sticks past the start position so i have to turn it back to run and it is fine. 2nd thing i just noticed tonight was my headlights. I was sitting idling then i reved the motor and the headlights got brighter. they were on low beams and i noticed this repeatedly on the way home. is this normal and i just have never noticed it? (wouldnt suprise me lol). 3rd is cd player problems. i think it may just be a loose wire to the cd player or maybe even the loose ignition switch cause this. it will switch on and off (generally when hitting bumps) and one night i turned my headlights on and it would shut on and off then i turn the lights off and it was fine. next morning this did not happen though just that one time. today i was leaving this morning and i was going along pulling out of my yard and the cd player died while i was pulling out, the aftermarket tach acted funny and the shift light came on and the motor started to bog so i pushed in the clutch and the motor came back to life (may of also jiggled the key not sure i was tired lol). Then when i left for lunch the cd player was shutting on and off so i smacked the dash and the whole pickup die and would not restart. the starter solonoid wouldnt click and nothing would work, but i could turn the key to acc position and the cd player turned on. so i pissed with the switch and nothing worked got out jiggled cables (power cable is new but i am going to replace it as i had someone pick one up for me and got one way longer than i needed.) did i just hurt my pickups feelings? what i think i am going to do is get new power and ground cables and check the connections for my cd player. anyone got and suggestions or anything? Also one thing i forgot is the blinkers act up. they blink slowly and sometimes they do not work and the light stays on the dash. usually though once i got for awhile they start working. i had problems just with the left blinker so i put a new socket in and that fixed it for quite a while actually. I figure this is pry turn signal switch and will replace it eventually if nothing else works. sorry for the long posts guys. hopefully i wont put ya to sleep. just figured id tell ya everything to make it easier to diagnose (if ya can stand reading the whole thing lol)

 

LOL, it's bedtime anyway.
1. Replace the ignition switch. I figured mine out in the driveway with the keys swinging right and left, motor kept time with the keys. :-P

2. Check the alternater belt. You should have a constant 13.5 volts (minimum) at idle.

Start here and let us know, Mike

 

Like hypoid said,

1. Replace ignition switch, go to blueovalparts.com and search 78-79 Switch - Ignition
Part # SW-0057, much of the electical problem is at the ignition switch.

"they blink slowly and sometimes they do not work and the light stays on the dash."
This could and is usually related to fixing a bad bulb or checking for a bad electrical connections at the sockets or a bad ground wire running from the electrical sockets.

 

well i got a new power cable and am going to put it on in the morning. Also i figured something out with the blinkers. i know this sounds weird but if it idles it either stays on (doesnt blink just stays on solid) or blinks very slowly. If i have the rpms up it blinks faster (like normal i think). I am wondering if enough power isnt going through the cable coming off the battery? Guess ill find out after putting a new one on. I think my electric choke is acting up. Damn electrical **** anyways. I will also probably order a whole new switch. I may keep my doors one key and switch another. ill decide later i guess.

 

WOAH!!! Slow down Josh.

I caught the diff between idle and above. Blinkers, headlights; what you describe is typical for low voltage. The battery is supplying power when the alternator should. If a wire is ratted out, go ahead and replace it. Typically, terminations are the biggest culprit for increased resistance.

Start with the simple and cheap before you spend a dime:
1) Is the belt in good condition, and tight?
2) Are the charging circuit connections (including regulater case to ground) clean and tight?
3) What is the Voltage output at idle, above idle?

If #s 1 & 2 don't straighten out #3, it's time to look at the alternator.

The ignition switch is changed separate from the lock, you can keep the matching key. Most any auto parts should have the switch for under $20. The switch problems you describe are classic wear. I've had a few fall apart in my hand after I took them out.

BTW, NICE TRUCK!

 

The alternator is only around a year old so it should be alright. I am going to check the belt and voltage output. I know i replaced a belt but i cant remember which one exactly. I am pretty sure that there is a lower voltage at idle compared to above idle. hopefully ill have time to figure it out tomorrow if not i know i will thursday i guess.

 

Just be cause it's been replaced doesn't mean it works... I've been there. My '73 has low voltage at idle too. At idle the headlights are dimmer and heater fan is slower, but as soon as I rev it up a little the lights brighten and fan speeds up. I've replaced the alternator, regulator, wiring harness, battery cables and added extra grounds with no change. I've just gotten used to it - it's been this way for 10 years now with no problems (other than annoying me...)

Marty

 

Check the fusable link from the starter solenoid bolt, the one nearest the battery. Check the connection where this fusable link, joins up with the wire coming from the alternator and voltage regulator (will need to cut into the wire harness to expose wires). Usually at this junction is a place where wires come loose or sometimes not a good connection.

Check the ground at the voltage requlator,
Check the negative ground cable coming from the battery to the engine. Make sure the connection are cleaned and tight.
Check the connection at the starter solenoid.