Left low beam and both high beams dim with low beam selected

Hi,

Good lord, this is an interesting one.

I spent some time going through wiring schematics and was only able to find one correlation between the two components. There is one ground that seems like it could be related. I attached three pics below. The first two show grounding locations for the lighting. Pic 3 shows a ground location for the starter relay. (ground 104 lower left of the engine) If you notice, that is the same ground used by the left headlamp seen in pic 1. Do me a favor. Check the condition of that ground. I have a feeling (and this is a theory) that when the light is in, somehow the power is back feeding and causing the quick engagement. That is where I would start checking simply because of the correlation between the two components.

I have to be honest, the grounds on these vehicles are somewhat poorly designed. When checking it, confirm that it is in good condition. Move it around to see if the connector isn't half broken. Also, make sure there are no corrosion issues.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know what you find or if you have other questions.

Take care and Happy New Year.

Joe

Joe, I love your initial reaction lol. First of all thank you for taking the time to investigate this issue. it's much appreciated. The truck is at the home i am moving to out of state so I won't see it for for ten days yet but I will get back with what i find. I agree the ground system is a pain. I did find one ground on the right side of the block that just broke off when cleaning it. So the condition of the wires themselves not just the connection will be checked out. I also have new battery cables coming for both batteries. Ain't electrical gremlins fun. Thanks again, I will post my findings.

Hi,

It is certainly unique. LOL. Listen, when you have the chance, let me know. I hope you had a good new years day, and have safe travels.

Take care,
Joe

So the issue has been resolved. I attacked all the grounds on the engine block, G104 and the others. Replaced about 1 foot of G104 wire as it was corroded. Cleaned up the block connection points and ground leads, added star washers and dielectric grease. Along with replacing the battery leads which were showing some corrosion migration up from the terminal ends. Also cleaned up the positive leads to the fuse box as they were looking bad at the Mega fuse connections. So not positive which ground was the issue as I went after them all, but most likely it was G104 like you said. Thanks again Joe for your insight.

Hi,

I'm glad you got it fixed. In all honesty, a bad or weak ground can cause more issues than you may realize. If it is bad enough, power will seek a new ground. As a result, you could have lights turning on, turn signal lamps turn on, and anything you can imagine.

Many years ago my first shop teacher taught me when it's electrical, start at the battery. Then check the grounds. LOL I wish he was still around. He was very knowledgeable.

Listen, if you have questions or need anything in the future, let us know. You are always welcome here.

Take care,
Joe

Thanks Joe, 37 years working on Jet aircraft and I've seen a lot but this one was crazy.

You are very welcome. Trust me, you're not alone. It happens to the best of us.

Take care of yourself and feel free to come back anytime in the future. You're always welcome.

Joe