I have a 97 ford ranger 4.0 V6 that blows fuse # 19 when the ignition switch is turned on. I replaced the fuse, the truck ran for three weeks with no problem, and then while driving it blew the fuse and cut off. I replaced the fuses again drove for about 30 mins blew the fuse again. Finally this week I replaced fuse, went on a test drive, and again it blew the fuse, but this time it keep blowing the fuse and the truck had ro be towed home, From that point I found that the green/purple strip wire from the ignition switch when giving power does blow the fuse. People seem to think that on this #19 fuse you have the P.C.M relay, pcm diode, and ignition coil, but that is not the case. I have read the forum responses and nobody really ever solved the problem. It is a short , yes I know. But I have to assume this has happened to someone else in this forum and they found the problem. I have already run every test, but today I got the truck cranked .But this might sound strange... I have a very low level of ground running through the positive side of the #19 circuit, after gigling the wires in the engine bay and the fuse box inside the cab. The test light shows a very dim bulb on that circuit so I do not understand what might cause the ground to increase enough to blow the fuse again. I am thinking I could take the easy route and run my own positive from battery fused wire to the ignition coil, Pcm relay, iac control, purge valve and purge valve sensor to at least keep the truck running while I am driving , but I cannot find a single wiring diagram on the coil , or under hood fuse wire diagram for the PCM relay on the internet. I have ordered the manual for the truck meanwille Any suggestions would be appreciated.

thanks in advance

 

Please explain better

 

Sounds like you have a direct short, but the resistance of the ground side of the circuit is abnormally high but intermittently drops to a point the current flow can blow the fuse.

 

I attach a test light to the battery positive, take test light and place it on the fuse terminal without the fuse and the test light admitts a dim light. Not a very bright light. Its a low level ground to short. A very bright light from the circuit tester would be a normal short circuit and honestly would make more sense to me. How can it be a low level short, so low it does not blow the fuse and the vehicle runs just fine. I am going to trace the wire back to the inside the cab fuse box. I was thinking someone might have ha this problem before.

thanks

 

Yes,.. but why....? I was hoping someone might have experienced this before. I an going to figure it out!! thanks

 

What, exactly, on YOUR truck does this fuse supply power to?

 

So far I found that it supplies power to the pcm relay, purge valve, purge sensor, A /c high idle sensor, ignition coil, pcm diode. But the Ford diagram says PCM relay and ignition coil.? I have the Haynes manual on the way maybe it will shed some light on the problem.

 

I failed to mention the computer is reading a short circuit code in the purge valve unit. Which is on the same circuit as# 19. So you would think problem solved if you unplug the valve. Nope.

 

How are you verifying the change in ground resistance is what's causing the fuse to blow?

 

​​​​​​I am using a test light.. I imagine I can use a ohm meter to get specific numbers. The truck wouldn't crank and would immediately blow the #19 fuse when the ignition switch sends power from the green/purple stipe wire. Upon testing I pulled on the wires going to the pcm, underhood fuse panel, and inside fuse panel. Suddenly the test light went dim after pulling on the wires. I then replaced fuse and it did not blow cranked up truck has been running every since. However I can't call it fixed until I can fix the short. I have been reading about the short circuit detection devices they sell it might help. I bought the habit freight cable tracker but it didn't help much.

 

Using a test light. Originally the truck wouldn't crank, and would blow #19 fuse when the ignition switch was turned on and power was sent to the green/ purple wire. I removed the fused and used the test light to check for ground in the circuit .Test light lit up. For example take a test light attach the to the positive terminal and touch the ground. Very very bright bulb. After pulling on the wires to the pcm, in cab fuse box and under hood fuse box the test the light went from bright to dim. Then I replaced the fuse and the truck cranked up and is still running. So yes it's obvious it's a short in one of those three places. I was hoping someone would have had this problem and would know.

 

Positive terminal of what? Battery?

Test one at a time, not all at once.

 

I just wanted to give a quick update to help someone that might be experiencing the same problem. First, order your Haynes or Chilton manual for a good wiring diagram. As it turns out the only thing that was on that circuit 19 load was what is listed by Ford. Second , a fuse will blow because you have a positive connection with a ground, could be chasiss or wire ground. Wire finders/ short circuit finders will not help you so don't waste your money. You must locate the color wires that are listed in the wire diagram follow them and find the short to ground. In my case I could not physically see the wires as most of them run behind the engine block. It is very time consuming but you have to carefully follow the wire from the fuse panel inside the cab to you find the short. In my case I did not. I would not recommend doing what I did, but it works. You can rewire the load from the in cab-fuse box. But first you have to make sure the fuse box is not your problem by checking the wiring and connections Number #19 runs from fuse panel to front fuse panel to PCM relay and diode then to the ignition coil and radio suppressor. I cut the wire running from the in cab fuse box, and replaced it with another wire, ran that wire to those circuits and have not had a problem. I connected the wire to those loads directly to the closest visible connection point to make sure to avoid another short to ground. Keep in mind before you can rewire the circuit you must make sure the components on that circuit are not the problem first, by disconnecting them one at a time when you experience the fuse blowing. Once you determined it is not a component in the system , which would be( Pcm relay, Ignition coil, or Pcm diode, or radio supressor). Once those components are eliminated and it is determended that it is a problem in the wiring you could rewire the circuit, or do the right thing and take the time to trace the wire otherwise you would be wasting your time. I suspect the engine was changed on my truck and the wires from the harness were rubbing up against the rear firewall behind the block, but without pulling the motor out who knows? I hope this helps someone that might be experiencing this problem. Good Luck.