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6Bucs, Ford Senior Master
Category: Mercury
Satisfied Customers: 872
Experience:  Ford Senior Master tech.
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I apologize in advance a novel, but it's an electrical

Customer Question

I apologize in advance for writing a novel, but it's an electrical issue, you know. I had a mechanic replace my alternator a year ago. My 99 V6 Cougar ran fine until about a month ago. One summer (hot) night, I was running with lights and AC on. I lost power on the road. Popped the hood and the positive terminal cable connector was glowing red. It had melted on the bottom side and dripped onto the battery, burning a hole into the battery.
I replaced the battery. Then I cut each of the positive and negative cables back a few inches (where they looked ok) and put on new set-screw dual lead connectors, not the temporary clamp-ons. I monitored the heat of the cable to see if it was working properly. No good.
I called a mechanic, told him the story, and he said replace the alternator. I called an auto electrician, told him the story, and he said it was def the alternator. I took the Cougar to an auto parts store and had them test the alternator on the car. When the headlights were on with the AC, it failed. Otherwise, it passed. He said to replace the alternator.
So I did the nasty business of replacing the alternator in a 99 v6. I had the old alternator tested again but off the car this time. It passed. I asked them to do it again. It passed. I took it to another shop. It passed there as well. Not knowing what else to do I replaced it with a new (not remanufactured) 130 amp alternator. And... no change.
I checked the continuity of the mega fuse and it's fine. I checked the continuity of the battery cable and it's fine. With the car off, I did a voltage drop test from the center of the positive battery post to 1) the new connector, 2) the new cable leading out of the connector, and 3) the set screw that joins the existing cable harness from the behind the engine to the new lead (where it gets hot). There was no drop at all. I repeated the same steps with the car and lights on. The cold cable set screw was too hot to touch within 2 minutes. The voltage drop between the post and the set screw was .4. I don't know if that reading is significant, fyi.
At the end of the day, I have a new battery, new alternator, new connectors, no more money, and still no way to get to work. Any ideas?
Submitted: 1 year ago.
Category: Mercury
Expert:  6Bucs replied 1 year ago.

Hello and thank you for your question. My name is James.

Can you try a voltage drop test from the center of the negative battery post to any of the body ground bolts that you can access in the engine compartment? Are you able to see the negative ground cable where it attaches to the body and the engine to check for corrosion? How about the positive cable at the starter? I'm guessing there's no corrosion or loose connection at the alternator, since you were in the area recently.


Customer: replied 1 year ago.
Hi James, I can't see where the ground connects to the engine. It's buried beneath a small belt/pulley on the top right of the engine as well as a radiator hose. However, a drop voltage test on the negative post and the engine itself reads 0.00, same as a test on the body and post. Continuity on both places reads .04. The ground to the body directly beneath the battery was clean but I cleaned it anyway. No sign of corrosion or burnt cables there.
Expert:  6Bucs replied 1 year ago.

Does the engine run now? If so, can you test voltage across the battery when it's running to see what the alternator output is?

Customer: replied 1 year ago.
With engine on, no accessories running, it's steady at 14.58v
Expert:  6Bucs replied 1 year ago.

Is it the same when the cables get hot? Is there any way you could upload a picture of the cable repair that you made?

Customer: replied 1 year ago.
Since I know it has the capacity to blow up, I don't run it hot. So I haven't tried to test it - that could be an expensive test. This photo shows what happened immediately after the cable repair when I ran the engine with lights on for about 4 minutes. It gets hottest around the set screw connection, although the entire cable gets hot.