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New ChevyDuty harness, new 12v alt with external regulator, new battery with 1 ga. cables and new ground strap (I even exchanged the alt & reg.)and a new headlight and dimmer switch, also new coil with resistor. But...tail light fuse blows with truck running after time, sometimes lights die or dim at intersections, horn blows for no reason, battery won't start truck even though it reads 12v, alt won't charge battery and now it won't even jump start. What is going on here???????

buddha,

It sounds like you have more than one problem. The common denominator is that someone put in a wiring harness, and all these problems are common to the WIRES. If you checked the battery with a reliable volt meter, and it read 12v, it means that it is discharged and probably won't start the truck.

Try and take this in chunks..with your meter, verify that the charging system is actually charging. Take the battery somewhere and have a load test done on it, or just have it charged..prove it is good so you can take it off the list of problems. Modern day alternators cannot charge a discharged battery. Trying to do so can ruin the alternator.

After you have a good battery, a functioning charging system, then attack the harness madness. It sounds like wires are not where they
should be obviously. Do the starting/charging thing first, then inspect all your harness.


Stuart

Thanks for the advice. I forgot to mention that I put in the harness. Seemed idiot proof, but they never met me! Seriously though, the Chevy Duty harness is pretty straight forward. I called their tech dept. and they suggessted an internally regulated one wire alt. But wwhat do I do with the wires that go to the regulator? I've read several posts here that speak up for for both types of alternator.

buddha,

If you already have the charging system in, changing to the single wire would just be fluff...a personal preference. I would keep the one you have now, get it working properly. De-bug the harness and you are all set. Later, after you win the lottery and have money to burn, call Chevy Duty. Good luck.

Stuart

Why won't it crank even when I try to jump start it?

buddha,

I think, because the battery in the truck is dead...electrochemically dead. It cannot pass the the current from the donor battery through its cells. If you left the jumper battery on it awhile, it would probably start the truck. I have tried to jump start rigs that had a dead battery, and sometimes, it just doesn't work.

Right now, I wouldn't focus on the jump start question. Use that time to have the battery load tested and/or charged. If you want instant results, put a know good battery in and see what it does. Make sure as you explore your system that you have good strong grounds from batt to frame and engine. Keep going, you will win!

I didn't ask, but I assume you have actually started this truck several times before these problems occurred..you mentioned driving around and have fuses popping!

Stuart

I have driven her a good bit. Today I'll take the battery back to the auto store as it is new. It's a budget battery and that may be one of the problems. Let me ask you this,,,Could the ignition switch be bad????

If it is I know where you can find a new nos one that will fit 49 to 54, only been out of box just long enough to look at it, still in the gm box it came in,,, regards...Fred

buddha,

It shouldn't be a factor in this instance. I think we are talking about a '49 pickup, so it probably has a stomp starter. In regards to starting, the key only energizes the ignition, the action of the "stomp" drives in the bendix and completes the circuit from battery to starter. It is two different things..."the truck turns over, but won't start" as opposed to, "the
truck won't turn over".

If the truck won't turn over, it's because it
hasn't enough juice or it has a defective starter. Start at the beginning..get the truck to start first. Did you keep the 6v starter? Have you tried a donor battery yet?

Don't buy a new battery until you rule the old one out by testing and charging it. There is still the possibility that it could be the starter switch or the starter. We started at the battery because it is the "usual suspect". Be sure to check your cable connections. Both cables must be clean and attached firmly..very important.

Stuart

Buddy, Stuart is very correct to make sure you have a good battery,,, had trouble a few weeks ago with my 70 international halfton, could not get it to crank even with a boost,, but when I checked the old battery out it showed 12 volts with my meter,,took it out checked it out at local auto-store, it was bad,, bought new battery,,, started up right away, had another issue but you have to make sure the battery is good. somtimes they will fool you..best of luck,,,Fred

Just replacing the battery could make it start even if the original battery was good. The cables could be making poor connection even if new.

UPDATE: Battery WAS bad. Hooked up new battery and tail lights, Tail lights work but I haven't run them long enough to see if fuse blows. Horn went off when new battery was installed so it is now disconnected. I may use an add-on button; there is no horn relay. Truck fired up nicely but alternator is not charging (checked with volt meter). I will take the alternator back for bench testing. Could the horn problem be causing the tail light problem as there is no fuse for the horn?

budda,

Wonderful news..and so fast. Good for you. I would not think the horn problem would cause the tail light problem, but I think it indicates the harness install might not be glitch free.

Now that the rig starts, get the charging system working properly. If you can disconnect the taillights like you did the horn, I would do that. You want the charging system isolated so you can prove it works, without any questionable wiring influencing it.

Because you have an external regulator, your alternator might check OK on the bench, but not be wired correctly in the truck to charge.

See what develops on the alternator test, and be sure to disconnect the battery until you resolve more of the problems.

Stuart

Your horn problem could be as simple as the horn button stuck or the wire grounded where it connects under the horn button....Did you replace the wire that runs up through the column to the horn button....Ronnie

Today I replaced the alternator as it was defective, however the new one is doing the same thing. It showed a slight charge then nothing. With engine running battery showed 12.29 volts. Meter read zero when battery post was grounded to fender. Alternator is grounded with front lights circuit on fender. All circuits work, but I have not replaced the horn wire in the column. Will leave it disconnected and wait until this bigger problem gets solved. I got three questions: 1). will taking out all the fuses help? 2). How can I safely jumper this Alt. to test it. 3). What pros and cons are there for internally vs. externally regulated alternators?

buddha,

Were you able to get someone to tell you what was wrong with the old alternator? Taking the fuses out sure wouldn't hurt. You can test the alternator on the truck by temporarily touching a jumper from the battery, or a battery source to the "F" (1) terminal on the regulator. You need a meter on the system when you do this. This test will energize the alternator field and make it charge its max. If you do this, and the alternator is good, the meter should jump to 14 + volts.

If some wiring glitch toasted the previous alternator, you don't want a repeat performance. I don't really understand what you meant about the battery post grounded to the fender. You don't want to pull cables when the truck is running.

A internally regulated alternator would have been a better choice from a simplicity standpoint. Study the directions that came with the harness. Verify all your regulator connections. #2 terminal should be switched with the key..key off, no juice.

Jumping 12 volts to the field terminal will tell you if the alternator works.

Removing the fuses can't hurt

Internally regulated gets rid of the troublesome regulator.

Sit down with a cup of coffee and study those instructions for the harness. The horn wire and taillight issues are minor. It is starts, which it does, and if it charges, which it WILL, the other things on the list will soon be solved.

Stuart

Thanks Stuart. I'll check this out tomorrow.

Before I go, the way I tested the alternator was to run the positive probe of the voltmeter from the battery post on the back of the alternator to the fender using the negative probe on the voltmeter.

buddha,

That would probably do it. I usually stuff my probes right into the battery where the cables clamp on. Of course on these rigs, the battery is in a remote location. Using my meter at the battery, I will set it on DC volts, read the battery at rest, then without disturbing anything, start the truck and read again. You should see an appreciable increase in voltage, somewhere in the 14.5 range.

You might get a helper and try it again using the battery posts. The fender might have been a poor ground. Be sure to run the RPM up to get your alternator cooking.


With the truck stopped, putting the negative cable on first, then the positive cable, you might see a very very small arc..if you see a big zap you have something shorting to ground.

If the battery was new yesterday, it sure doesn't seem like it should be that low now. 12.6 volts equals 100% battery charge, and, hard as it is to believe, 12.3 volts is only a little over 50% charge. I knew this was going to come up, so I did some "battery basics". We both get to learn!


Stuart

Sorry it took so long to get back here. I have replaced the alt., reg and battery and the charging system is NOW working. I have also installed new tailights, but haven't had time to road test them yet to see if the fuse will blow. I think the problem may still be with the horn. I have disconnected it. I was going to buy one of those push button add-ons that stap to the column but it had is an open switch design where the hot wire comes in one side and out the other. Push the button and you complete the circuit. Problem is there is only one wire running up the inside of the column and I think the short is there since the horn would come on for no reason.

Connect the one horn wire to the switch & ground the other term.

Took the truck out today to buy a Christmas tree. Drove with the lights on. Got to where I was going and the tail light fuse was blown. Put in new fuse, returned home at sunset. When I started the truck, all the lights flickered until I drove out of the parking lot then the headlights and dash lights worked fine but tail lights were out before I hit the highway. I drove home with the flashers on.. I had after-market turn signals installed and they work without the key. Could this be the problem? Could the brake light switch be the problem? Rear turn signals and brake lights work fine and aren't effected.

Hy buddha, Its always interesting trying to do diagnosis by braille and long distance. Flickering lights, bad power connection at light switch or at feed source to light switch. Tail lights burning out fuse, I assume the fuse is adequate for the circuit, are there any other lights that are on with the tail lights, parking lights? We must isolate the circuit in question, Obviously the tailights are not shorted to ground at the bulb holders because your brake lights/turn signals work okay. How old is your light switch, the flickering could be a bad connection to the switch,or a bad connection through the switch, bad connections cause heat which causes resistance which raises amperage which may cause your fuse to blow, other than that the tail light wire may haved chaffed through somewhere on the way to the tail lights

The headlight switch is a new after market one. The fuse is 20A. I think the park lights (front) have their own circuit. I'll check that today and back with you. Buy the way, as always THANK YOU to all who give me info on this forum.