This is for a 1991 3.0 engine. The battery (Optima Red) and starter are both new, so they should not be the source of the problem.

Here is what is happening: I go to start the truck, and all electrical power is normal when the key is in the accessory or run position, but when I push it all the way to start all electrical power is lost. Moving the key back to run or accessory has no effect, no elctrical at all. If I jiggle the positive cable I can hear the starter relay click from the passenger side firewall area, then electrical power comes back, but more often than not, all power is lost again when I try to start it. If I can get it started, it runs fine, but if I shut it off, it won't start again without jiggling the the positive battery cables again.

Okay, I know, "check the postive cable connections, Scott!" I have done a quick check of them, and visually they look okay. Almost all of my tools are at another house right now, so I don't have a way to disconnect the cable and give it a good once-over, or even replace it. I'm just looking for other ideas from people who may have had similar problems. I know zippo about car electrical, but it just seems weird to me that the blackout doesn't happen until I turn the key all the way to start, I would think it might happen sooner than that??? AND, I can't imagine how a bad relay would cause it either, but again, I know almost nothing about car electrical.

Any help is much appreciated!

 

I had an '84 that about once a year it would totally lose power and die. The battery and cables weren't very old and they didn't look corroded at all. But, after disconnecting the cables, I saw a sticky,wet, clear film on the posts and inner part of the connectors on the cables. I cleaned them and sdanded them and didn't have any more problems. Just every other oil change I'd take them off and clean them just in case.

 

Likely is is the increased current draw when you try to start that causes the power (voltage) to drop. All you need is a crescent wrench to loosen the battery clamps for a check. I use one of those battery post/clamp brushes from an auto parts sotre to clean mine. Plastic tool with a hollow end and wire brush inside that you slip over the battery post and give it a few turns. On the other end is a round wire brush to clean the inside of the clamp. Slide it back on and tighten it up carefully. One thing to check is that the clamp is really tight and not just the clamping bolt bottoming out before getting the clamp tight. I had one clamp that was a bit deformed and the ends would come together and the bolt would get tight, but if you pulled on the cable, it was still loose on the clamp. Don't forget the ground cable as well. If that does not help, pull the cables off and inspect the ends where they meet the clamp. Sometimes, the conductors under the insulation can be partially corroded or broken and it'll still look OK with a quick look.

 

Yeah, I think it is where the starter cable clamps to to battery clamp. I jiggled it under the wingnut, and it fixed the problem for a bit, though the nut is tight. I still haven't taken it apart, but I'm thinking now I just need clean off the cable ends real good. We have also had a lot of freezing nights and days hear lately. I'm wondering if moisture from our foggy nights has crept in there, then frozen, causing trouble. I wouldn't think it would, since water is a conductor, but this just happened when it started getting really cold.

 

I ran into this a while back as well. Found bad connections at the pos. battery terminal. The wire that runs from the Pos. terminal to the fuse box is prone to corrode, eithor at the battery end or the fuse box. Check both sides of the connection. Hope that helps.