nothin but the horn works

[boyle05]

need some help with a major screw up. don't ask how, the battery got hooked up backwards. it was just for a couple seconds and believe it or not the thing ran and worked great for about 24 hours after this happened. i had a feeling that we would not get away with it though. we were driving it today and it just quit, like my 1979 did a few years ago and it was the control module. this is a 71 f100 with a 351 from around 1985. it has the module with a 4 wire plug and a 2 wire plug, blue connector on the back side. i noticed when replacing it today that the yellowish wire on the truck side of the 2 wire plug is not hooked to anything and i did not find a loose wire in the area. so only one wire from the 2 wire plug is wired into the truck, not sure what the yellow one is. we also replaced coil, solenoid on the fender well by battery, regulator on front by radiator, and put a new ignition switch. none of this got me anywhere. i checked fuses, and wiring for burnt spots. so, right now i have nothin but the horn working, no lights, no starter, no hazards, not sure where to go next. the truck had manual transmission so nss wires are factory looped, even if these were burned into it would not make my headlights and interior lights not work, right? i will pull fuse block off tomorrow and check wires behind it. any suggestions would be appreciated.

[fordman]

the yellow wire if its the one i am thinking about goes to the battery side of the relay on the fender behind the battery. it goes to the battery side of the relay. not the starter side.

[boyle05]

i want to make sure i understand and that i was clear. the yellow is on the engine side of the 2 wire plug to the module mounted on driver side fender. you are saying that it may need to hook up on the solenoid by the battery on the passenger side , i am not sure what relay you mean. i am almost afraid to connect that wire to anything as i should be able to find a stray wire near it if it was connected before. we have had the truck for nearly a year and it has run fine until the battery deal. i pulled some tape off to check the wires from the module. the wire from the 2 wire connector that is hooked up ( i think it is red )
is spliced with two wires on the truck side. maybe the extra wire that is connected here is the yellows mate? i will be able to take a better look at it tomorrow i hope did not have much time to look at it today before it got dark. it sits in a church lot about a mile from the house. thanks for your help

[fordman]

sorry i was talkign abotu a different wire. i know nothing about module wiring. i would have to be there to help with it. i cant do it by memory.

[Dragon]

The starter would have spun backwards if the wiring had been backward. That is the rules for DC motors reverse the polarity to reverse the direction. What yellow wire? YOu could have fried the module by wiring it backwards but the rest of the truck except for the radio would not have cared.

Here is the wiring diagram for a blue connector (Duraspark II)

[Thunderfoot]

right now i have nothin but the horn working, no lights, no starter, no hazards

With you having NO power going into the cab of the truck, you need to use a Test Light and check the "Black/yellow striped" wire that is connected to the battery side of the starter solenoid for power, and keep checking it as it goes into the cab. This wire it the main power wire into the cab for everything... either the wire opened up somewhere or the connector where this wire plugs into the cab came unplugged or is not making connection for some reason...

The fuse block won't be your problem as the power to the lights doesn't go through the fuse box... (just points to no power in the cab with everything not working)
The horn works because it gets its power from the relay on the fender, this relay is a ground activated relay so the switch in the steering wheel for it just makes a ground connection to activate the horn relay... no power from the cab for this...

[fordman]

what about a bad ignition switch?

[Thunderfoot]

what about a bad ignition switch?

That won't effect the power to the lights (headlights/tail lights), with no power to the lights it is a problem with the main power wire into the cab...

[boyle05]

thanks for the info. i was not able to get to it today, it was dark by the time i got home. i will check the main hot wire. it just seemed strange for it to work for a day and then lay down. i took the module to auto zone and their machine said it was dead. it must have popped the wire almost into and when we were driving it went the rest of the way. we have replaced the module, coil, regulator by radiator, solenoid by battery and ignition switch since this happened. needed most of them anyway. after looking at some of the schematics on the site for the module last night i think the yellow wire i was referring to was actually the white wire that runs with the red wire in the 2 wire plug from the module, i guess the years had turned it a little. something i have noticed is that the starter relay in most of the diagrams has only one push on plug on front and mine has two with a wire attached to both. i notice in the diagram sent by dragon there are two posts. we did not actually try to crank it with it basackwards. it sparked and we pulled the wire off within a second or two. i feel you guys are correct about the main hot wire, it may be this weekend before i get a chance to get into it again. thanks for all your help.

[Dragon]

On the vehicles with a resistor ignition wire you get a 2 small post Solenoid On a straight wire to the coil you get a single post Solenoid. The second post provides full voltage to the coil bypassing all the stuff dragging down the available current at the ignition switch.

[fordman]

these truck originally had the two small posts in the center of the relay. the single post is for a electronics igntion equiped truck. 73=79 still used the same relay but they didnt have a wire on them i think. the 80's truck definetly had only one small post on the relay.

[boyle05]

well we went in the dark tonight and got it home. it was driving me nuts leaving it out there. i found the yellow/ black and traced it. it actually ran to the alternator and a red wire from the alternator came to the battery side relay post, instead of the y/b running straight from the cab to the post. some of the wiring was obviously rigged when the 351 was installed. also the stray wire i found from the 2 wire plug on the module had to be connected with some others i found in the bunch before it would start, it would crank but not fire. they have the 2 wires run together with their mates from the engine side into one tie. we still have some issues. no brake lights at all, not even with headlights on, left blinker won't work with the headlights on and barely works with them off. when i first started it the fuel gauge went to full and i know it only had 1/4. the oil pressure gauge went to the h. these two came back to where they should in about 3-4 min. of running. not sure what the deal is with all the light stuff but at least we have it home now. thanks for all your help.

[boyle05]

got into it yesterday and found that the weird light stuff was caused by the taillights. the driver side had exploded and the pass. side had blown. i replaced these and it seems to have cleared everything up. still looking over my shoulder though for other ghosts in the machine. thanks

[fordman]

crossed wires in the bulb. wierd that made it not want to start.

[Dragon]

Maybe just maybe too much current was going to ground as a resistive short to prevent the coil from getting enough current.