1990 Wiring Question
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From: las vegas, nv
1990 Wiring Question
On a 1990 F-350 Crewcab XLT Lariat an 8 amp fuselink fried the other day and the truck would not start. On start up was when the link failed. After bypass it would only crank. There is no 8 amp fuse link in any of the schematics I can find. They show the other 3 on the vehicle but not that one. Any ideas on where to start would be greatly appreciated. 
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From: las vegas, nv
It is a gasoline engine, the wire color on either side of the link is yellow and it attaches to the starter relay on the right fender on the same terminal as the battery cable and therefore hot constantly.
Thanks for any advice.
Thanks for any advice.
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From: Virginia
The fusible link you are talking about is the main one that feeds everything on the truck except the starter. I think it would be a "8 gauge" not 8 amp. It's more like a 75-90amp fuse.
Anyway, for that to burn out you would have had a serious problem with the wiring somewhere, or you were working on something with the battery connected, and had a little accident with the wiring. Follow the yellow wire from the fusible link and you should run into some splices and some more fusible links. If part of the truck is still dead, then I would check all the other fusible links, since it may have taken another one out, and that part of the circuit would be dead. Also check all the fuses, since some of them could be blown too.
Anyway, for that to burn out you would have had a serious problem with the wiring somewhere, or you were working on something with the battery connected, and had a little accident with the wiring. Follow the yellow wire from the fusible link and you should run into some splices and some more fusible links. If part of the truck is still dead, then I would check all the other fusible links, since it may have taken another one out, and that part of the circuit would be dead. Also check all the fuses, since some of them could be blown too.
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Sorry it was an 18 ga fusible link. Discovered no power to pin 3 on the ignition module. Then found no power at one of the terminals on the ignition switch. Replace it. Still no power to the pin 3 on the ignition module. Discoveered that the fuel pump relay was melted to the pig tail. The pump woul run so didnt start there. The relay and pigtail in the vehicle was a bosch and not original. Went to Ford to get a new relay and pigtail but was informed all the colors had changed. Need to figure out which goes where on this new set up. Ford could not say as which lead was which on the relay and it is not labled. Going to make a trek to the junk yard this morning to see if I can get my hands on the original pigtail.
Not sure if this will solve the problem but needs to be addressed. How does the relay comunicate with the rest of the system so as not to sent voltage to the ignition module?
Wasn't working on the vehicle at the time of failure, it occurred upon start up when leaving work last Mondday. Got in cranked and that was when it went kaput.
Not sure if this will solve the problem but needs to be addressed. How does the relay comunicate with the rest of the system so as not to sent voltage to the ignition module?
Wasn't working on the vehicle at the time of failure, it occurred upon start up when leaving work last Mondday. Got in cranked and that was when it went kaput.
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From: Virginia
The fuel pump relay wiring problem may have started the whole thing. In this diagram
http://www.autozone.com/images/cds/g...3d800a3a4d.gif
I would think it would have at least took out fusible link "w" and we know it took out the main fusible link. They wrap all these wires together for neatness, but if one circuit melts, it can take out some of the others that are wound with it. I wish I had a factory diagram that showed the power distribution with all the fusible links, but I don't. I think you still have a major part of the truck that doesn't have power. If you look at the diagram above, you will notice the red/green that sends power to the ignition module, also sends power to the EEC relay which powers most of the engine controls. If that fusible link is out, or the red/green does not have voltage, that would kill the engine electronics.
I believe the EEC relay is over next to the fuel pump relay, so maybe it took it out too.
http://www.autozone.com/images/cds/g...3d800a3a4d.gif
I would think it would have at least took out fusible link "w" and we know it took out the main fusible link. They wrap all these wires together for neatness, but if one circuit melts, it can take out some of the others that are wound with it. I wish I had a factory diagram that showed the power distribution with all the fusible links, but I don't. I think you still have a major part of the truck that doesn't have power. If you look at the diagram above, you will notice the red/green that sends power to the ignition module, also sends power to the EEC relay which powers most of the engine controls. If that fusible link is out, or the red/green does not have voltage, that would kill the engine electronics.
I believe the EEC relay is over next to the fuel pump relay, so maybe it took it out too.
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Been working on it most of the day. You are right red/green no power. Started hunting in one of the connectors on the drivers fender found power in and non out. Repaired checked coil and distributor and had voltage. Crossed my fingers and turned the key and voila. The day it failed, it had rained that morning don't know if water was sitting there and that shorted it or what but all is good now.
Thanks for your input. Best wiring diagram I was able to find was by
Thanks for your input. Best wiring diagram I was able to find was by
DATA RESEARCH BY AUTOMOTIVE HOBBYISTS.; Found them on-line and cost $11.99. You can download a pdf of whatever you order and honestly it was better than what the parts counter @ Ford had.
