Gen light stays on and kills the battery

[Rus-T65]

This is an issue I had a few months ago and resolved it by replacing the voltage regulator. A couple of weeks ago, it happened again. When the ing key is in the off position, the Gen light comes on. It is not on when the truck is running.
Today I replaced the 37amp alternator with external voltage regulator with a 60amp "one wire" alternator. I disconnected the VR and have only the "one wire" coming from the alt to the battery. The horn relay is in the middle and there is a heavy guage red wire leading to the dash.
I have been scratching my head over this issue and thought it was the VR, then I disconnect it, the issue came back.

What am I missing here?

Thanks for your help.

 

[drabo]

Check the alternator. Using the ohmmeter setting on a multimeter place on lead on the case of the alternator and the other lead on the terminal check reading. After that swap leads and check reading. If you had OL one direction and a reading in the other direction then the regulator is good. If you had a reading in both directions then the diode in the regulator is bad. When the diode fails it will allow continuity in both directions basically, it will work like normal and drain the battery when it is not running. You can get by with unplugging the one wire when you stop, but this will get old quick.

If the regulator is good then check the starter solenoid. Or you might have a short somewhere.

 

[Rus-T65]

The alternator I installed yesterday is new and this happened with the old one too. I had the starter tested yesterday and it was good.

Thanks for your help. I will try the testing you suggested later today.

 

[Rus-T65]

One more thing. At the horn relay, there are 3 10 guage wires that intersect there. One goes to the battery, one goes to the alternator and one goes to the dash. They are connected at the same place at the horn relay.

If I disconnect the wire going to the dash, the light goes out and nothing works inside the cab, lights, radio and cant start the engine.

Hope that helps.

 

[dvalentine]

When you first had this problem a few months ago, what had changed on the truck ?? Did you just do ANYTHING related to wiring before the first failure??

The wire coming off the horn relay supplys 12 volts to the fuse panel, that's why nothing works after you disconnect it.

Get your hands on the cab and frontend wiring diagrams and verify everything is where it belongs. Remove any creative wiring patchs done over the years and get it as close to factory as possible...

THEN see if you still have the problem. It's a pain, but it will make future electrical work less mysterious and a lot easier to deal with.

dv

 

[Rus-T65]

Nothing was changed on the truck before it happened the first time and I had the truck for at least 6 months before it happened. I think I posted on here back then. I replaced the voltage regualtor and the issue went away.

This truck has not been messed with as far as the wiring. Its fairly clean.

 

[Rus-T65]

drabo, I did the alternator checks you mentioned and it checks out fine.

On the left side of the fuse box, there are connections that items can be connected too. My air compessor is connected to one, and a horn is connected to another. I disconnected both of them and nothing changed. I was going to start removing one fuse at a time to see if anything changes. That may help nail down which circuit may have an issue.

 

[drabo]

Sorry I can't dive too deep into your wiring problems. My diagrams are in Florida and I'm in the Middle East.

It sounds like you have a short somewhere. Sometimes when you have this type of problem there is not enough continuity to blow the fuse. If your lucky it will get worse and you will be able to see it. Look for a group of wires that are taped together that is not factory and make sure the connections look good. Check components that are not supposed to have power for voltage (test light is the way to go for this).

You might look into replacing your harness if it is in bad shape. The wires should not have any cracking on the insulation, discoloration and should be flexable. If you have these signs it is time to swap it out. If you are handy with wire stripers and a crimping tool you can make your own harness. There are a couple places that sell replacement terminals that lock into our factory harness.

They way I did mine is I routed the wires one at a time and held them together with zip-ties. While it was zip-tied I used Black Scotch #33 (or #88)to tape it together and removed the ties as I went. Also tape your mounting taps back in as you tape. When you are done it should look factory, splice free and clean.

I also upsized most of the wires. Lights had #16 AWG and was replaced with #14 AWG. All of my lights are nice and bright.