This 2000 Ford Escort was towed in, unable to start. Piece of cake, I thought, as I walked out to the car, jump box in hand. The first symptom I noticed was unusual though...the MIL was on, dimly, even with the key in my hand.
I verifed the complaint by attempting to start the engine. Nothing...no power to any system in the car that I could see. I popped the hood and hooked up the jumper, and tried again.
Still nothing.
OK, not likely just a battery issue. I gathered up some help, and pushed the car into the shop for a closer look.
The dim MIL, even with the key out of the car, bugged me. I tested the battery and it passed with flying colors. Next step was to check the fuses since the main junction box is right next door. The next clue was power at both headlight fuses...12.6 volts on one side of each fuse, and 11.6 volts on the other side. Actually, in hindsight, this was two clues. A 1.0 volt difference from side to side, and power on a fuse that is only "on" when the headlights are on. And they weren't.
With the key on, the MIL regained its normal illumination. But that was it. No dash lights, no instrument function, no radio, power windows, nothing.
OK, so why was there power at the headlight fuses? I must be dealing with a problem in the main power feed to the car...between the battery and the ignition maybe. Let's unplug the ignition and see what happens.
Still have power at the headlight fuses.
Now I'm getting a case of "tunnel vision" and start unplugging connectors from the fuse box thinking there is some type of short to power there. From the schematics, I thought that was the only common link left. First, I removed the headlight relay...the source of power to the fuses...and the fuses were still hot. I opened up the fuse block to look for visual damage and found none. Time to walk away for awhile and rethink things.
My decision? Get back to basics. It was in for a "no start" complaint, and that means starting with the battery. I had already tested the battery itself, and found it fully functional. Next step was to test for voltage drop, and considering I saw this:
checking the ground side first sounded like a reasonable next step. I turned the headlights on to get current flowing, and measured 2.65v drop between the negative battery post and the cable just behind this "universal" clamp! Removing the cable from the clamp it was easy to see the reason for the replacement terminal...corrosion on the wiring was obvious. I trimmed some back, and reconnected to see if I was on the right track. With the headlights on, there was no more drop across the terminal, but the problem remained.
OK, let's go all the way to the load and check again. Using the left side headlight as my test point, I measured 1.54v drop between the headlight ground pin and the battery post. Tracing back, I continued to measure this drop all the way up to the battery ground cable attachment point just at the firewall on the left side of the engine compartment. The ground cable on the Escort actually attaches to ground at two points on the one cable, with these two contacts in series with each other.
Looking closely, I could see a deformation in the insulation between this point and the battery terminal. Just past this point, on the battery side, drop returned to 0.0v. For testing, I cut the cable past this point and retested. No more drop. Now for the real test.
The dim MIL was gone. I was rewarded with full power when I turned the key on, and the car started normally and ran smooth. For giggles, I cut back the insulation at the deformation and saw this:
This photo is of exactly what I saw. The corrosion that caused the failed terminal traveled well up the cable and actually chewed through most of the strands.
A new ground cable was installed...