Truck electricity problem

[gordie4659]

I pulled a real smooth move on my 1970 F-250. My horn was not working so I wanted to test it by jumping to the battery to see if it was the horn or the relay or something else. I reversed the polarity by mistake and back fed 12 v to the system. Now the truck is dead. It is like the battery is disconnected. I checked the back of the fusebox and there was no blue or black discoloration so I don't think it got to the box. My question is, would this have blown the resistance wire in the ignition and would that break cause the loss of all power? I have a factory manual from ford but there is no troubleshooting. It tells you how to bypass the original resistance wire for the ignition in the wiring harness but not where it is. Could anybody help me out with this.

[fordman]

Before you cut any wires. Remember the resistor wire gets power through the ignitiin switch. If there is norhing when you turn the key it may be the wire between starter relay and ignition switch. See where u have power to and where you dont. The reaistor wire only gives power to the coil after the ignition switch is turned on. The resistor wire usually green goes up toward the upper center firewall. Then a shirt section of pink reaistor wire. Then green goes to the plug and wires that go out through the firewall to the engine in a group of 3 wires. You could have fried the starter relay too. I did it once myself. I got it too hot. Melted it.

[gordie4659]

Well, I did a voltage test on the starter relay and it was bad. When I took it off it was scorched on the bottom. I disconnected both battery cables and then replaced the starter relay with a new one. I reconnect the positive first and when I connected the negative cable the engine turned over for just a second and stopped. The key was not even in the ignition. It was like there was a charge built up and then discharged. So then I go to the cab and try to start the engine and there is nothing. I mean no clicking in the starter relay. But this time I turned on the lights and there is a very faint glow in the filament of the bulbs. Before I replaced the starter relay there was nothing anywhere. No lights, nothing. The fuse box is ok and all fuses good. I'm going to continue testing but something else was damaged and now there is not enough power getting through to even energize the starter relay when I turn the key. Thanks so much for your help and it allowed me to find the fried starter relay immediately. I will continue to work through the charging system and see if I can narrow the other problem down. Any other help would be wonderful.

[fordman]

Charge up the battery and have it tested if u dont get any more power out of it.

[gordie4659]

Yep, did all that and the old battery was not that great but the battery that I swapped in had all good cells and had a 12.44 volt test reading. Still the same thing. After finding the fried starter relay I thought for sure the problem was the battery but I got the same results, just a small glow in the headlights and it will not start. I'm putting a charger on the fresher battery. Make sure it's topped off. I'm trying to figure out how to test the wire from the ignition to the starter relay. It would be a resistance test, right? What should the reading be? I got to looking closer and someone before I bought the truck put a red battery cable on the ground to the engine and the positive cable was black, no wonder I reversed the polarity, I was looking at colors. Any more ideas would be welcome. Thanks for your help.

[gordie4659]

I was able to jump the starter relay and the truck started. When I tried to turn off the truck it didn't shut down. The ignition has no effect. All the lights work when I started it except the turn signals, the blower motor for the heater and the dome light. All fuses OK. Did a test of the battery and it was 12.20 when the truck was off and 12.35 when running. I think it could be the alternator not putting out enough. Might have blown the blower motor and the flasher when I reversed polarity. Have the alt checked tomorrow.

[fordman]

The dome should work with keep off. Blower only works with key on. On the starter relay the red wire goes on the front small terminal. The brown on the back small push on terminal.

I think 12 volts should be at the ignition switch from the relay.

If truck wont start or shut off with key. I think the small terminal wires are mixed up. Or the wires to switch could be bad. Or maybe the switch. Or the relay you put on is no good. Or possibly the wrong one.

Check what u can. Let us know.

[gordie4659]

I had the alternator checked and it was fine but it wasn't charging the battery. I tracked down the battery wire coming from the alternator to the battery and it was burnt out. I repaired that and checked the other wires from the alternator to the voltage regulator to the starter solenoid. I very carefully unwrapped the wiring harness and kept it together with zip ties so I could see what was going on. I didn't mix up any wires. I'm sure of it. All Ok and good continuity. I did everything correct and the terminal wires were not switched because I took pictures and labeled everything with tape. Now when I put the battery cables back on the battery the starter turned over and the truck started. Again, the ignition switch had no effect. I am going to get another solenoid and a new ignition switch. Why would the starter turn over when I put the battery cables back on unless the solenoid was fused with a closed circuit? Any ideas?

[fordman]

Have you ever seen a rebuildable gm starter relay? Inside of them look just like our relays. They are basically a electromagnet at the bottom is a disc. On each side the bolts the bat and starter wire. When auctuatwd the disk moves up and down and makes contact with all four bolts. Making the circut. If you could take apart our relays you could flip the bolts over if they had gotten melted on one side. So if you hace melted bolts inside the relay it could either not work. Or work all the time.

[gordie4659]

How would I do a bench test on that solenoid? I'm going to continue to track down the wiring in the entire harness and see if I can find the problem. I'm keeping all the wires in the same shape of the original harness and putting zip ties where it branches etc... looking for scorched wires, breaks and checking continuity. I'm putting in a new ignition switch and running down every wire I in the ignition and charging system. I'm doing all the tests like from coil to battery and ignition to coil etc...Have any suggestions or short cuts? I'll keep going. Thanks

[fordman]

To test the starter relay remove the cable to starter. Jump relay from large front plug to small front plug. It should give power to the rear two bolts / lugs small and large. That means it is enguaging. If you stop jumping it and still have power to rear plugs then it is stuck on.

[fordman]

I got a pic for you. I posted it on craigslist. So it will expire in 45 days unless some idiot flags it. http://lawrence.craigslist.org/vol/4893496314.html

[Nitekruizer]

The pink "Resistor Wire" doesn't do anything except reduce the voltage to the ignition coil to protect the coil and the points. It has no effect on the rest of the electrical system.

I doubt if you could have blown your heater blower motor. If anything, the motor should just have run backwards temporarily. The motor is made to run on 12 volts and you couldn't have exceeded 12 volts, even if you caused a dead short.

[gordie4659]

sounds good, thanks for the pic. I tested the new (cheap china crap) starter relay and it had fused shut so the starter engaged when I connected the positive cable to the front side of relay. I got a made in USA lifetime warranty one. I got a master wiring diagram and blew it up really large and that helped track things. I did a complete continuity test on the ignition switch according to the manual and everything checked out. I also make sure the ignition switch was grounded better to the dash. There's a backing plate that the front bezel screws into and makes everything tight and that was loose and I fixed it. I'm continuing to check continuity on every wire I can think of that would have anything to do with the problem before I put the battery in. Then I'm going to do all the voltage checks etc. according to the factory manual before I fire it up. I have enclosed the master wiring diagram if anyone is interested.

[gordie4659]

I tested the coil. Good resistance. Used a good relay and everything worked. I did put an electronic ignition module in the distributor cap and it was running great before the problem but now it wont start. I think I blew the electronic module during all this rigmarole. I was reading some other guy who loved the electronics until it broke and it stranded him. He went back to points. I might if I can't get my $70.00 back or a replacement. All the lights, turn signals and blower motor are working. I think the problem was between a bad ground in the ignition switch and a piece of crap Chinese starter relay. You have been a great help. I'm learning so much through this process and I hope I can help somebody in the future. I have a Ford factory manual for 1970 trucks volume 1 thru 5 so ask away.