Chevy truck loses voltage at 50mph when towing boat

[truckermatt]

Hello,

My 98 Chevy k1500 has a weird problem,

When I am towing the boat (4 way flat connection with surge brakes)... My volt gauge fluctuates from 14 (normal) to 11.5 about every 10 seconds in each location, and the battery light comes on (only at 11.5 volts), but only at 50 mph and above. Nothing happens below 45mph, it stays at 14 volts.

It started about 2 weeks ago when towing the boat home. But since then I have not noticed it happening without the boat at any speed.

Any ideas what is happening. The battery is 7 years old. and the lights on the trailer all work fine. (they are off when this happens)

 

[smoedog]

Re: Chevy truck loses voltage at 50mph when towing boat

how many rpm's are you turning at 50? sounds like a bad regulator

 

[T_Herrod]

Re: Chevy truck loses voltage at 50mph when towing boat

Remove the alternator and take it to your local parts store to be tested. If it checks out ok start looking for a defective ground wire on the vehicle.

 

[truckermatt]

Re: Chevy truck loses voltage at 50mph when towing boat

at 50 mph in 3rd gear i am at about 1800-2000 rpms What regulator might you be referring to?

I will try testing the alternator.

The weird thing is that it only happens when the boat is being towed.

also the alternator is 3 or 4 years old

 

[LippCJ7]

Re: Chevy truck loses voltage at 50mph when towing boat

The first thing you need to do is take your battery and get it checked if you don't know how, then get your alternator checked, then your connections, I don't mean this to sound as though you check the battery and if need be replace and see if you have a problem etc etc I mean check each of them out regardless of what you may have found to be the problem.

Your alternator probably has an internal regulator anyway so simply getting it checked properly should be enough.

If you have a Digital Volt Ohm Meter and know the basics I can tell you a few places I would check if I were having the same problem.

Also do you drive your truck at night and do you have the same problem with the headlights on? That would answer alot about the charging systems health.

If everything checks out I would check for a fairly substantial short on the boat trailer on an unprotected line(no fuse).

 

[UncleWillie]

Re: Chevy truck loses voltage at 50mph when towing boat

Even if the Alternator/Regulator were to suddenly stop, a battery that could go from 14 to 11.5 volts in a second would never be strong enough to start the vehicle.

I would suspect a bad connection to the battery.

 

[JEBar]

Re: Chevy truck loses voltage at 50mph when towing boat

as one who makes absolutely no claim to being a mechanic, wouldn't the boat wiring be a good place to place to check first if the only time the problem happens is when the boat is being towed

Jim

 

[truckermatt]

Re: Chevy truck loses voltage at 50mph when towing boat

thanks for the replies guys so far. As for driving with the headlights on, I dont notice any dimming or voltages changes.

I will look closely over the trailer to find a short, but I still find it weird that nothing happens below 50 mph WITH the boat being towed.

 

[oregoncruiser]

Re: Chevy truck loses voltage at 50mph when towing boat

thanks for the replies guys so far. As for driving with the headlights on, I dont notice any dimming or voltages changes.

I will look closely over the trailer to find a short, but I still find it weird that nothing happens below 50 mph WITH the boat being towed.

The faster you drive, the more voltage the vehicle reqires in order for the engine to fire. Over 50 with a load will require more power (Electrical power) to run.

I'm in agreement that the internal regulator could have a problem. Around here you can take the whole rig to autozone, or Knechts etc.. and they'll test the entire system without removing anything. I'd start there

 

[Chip Chester]

Re: Chevy truck loses voltage at 50mph when towing boat

Go out with a buddy in another car, get your rig to exhibit problem, then unplug the trailer and try it again. (Buddy drives behind you as buffer from other traffic during test.) See if it's trailer electric, or just presence of trailer.

My first thought was trailer license plate bracket causing short to ground at speed. Ground only being made when wind resistance on boat develops sufficient force on hitch ball to make contact thru grease. But that would be nuts.

 

[EddiePetty]

Re: Chevy truck loses voltage at 50mph when towing boat

......... Ground only being made when wind resistance on boat develops sufficient force ..... But that would be nuts.

Not so fast there Chester!!!

From the OP's discription, I kinda suspect a shorting condition on the trailer or at the flat-four connector at speeds above 50 due to ill fitted lights or wiring flappin' in the breeze!!!

 

[LippCJ7]

Re: Chevy truck loses voltage at 50mph when towing boat

Not so fast there Chester!!!

From the OP's discription, I kinda suspect a shorting condition on the trailer or at the flat-four connector at speeds above 50 due to ill fitted lights or wiring flappin' in the breeze!!!

My sentiments exactly however he also said his battery is 7 years old.

First thing you do when looking into electrical problems is checking that the system as a whole functions properly, Battery, Alternator and all associated cables and connections, once these are all verified good then you move on, in this case once I verified that the truck is good I would measure ground resistance from the battery negative post to the trailer which would mean extending a line from the battery negative post to my DVM and then several places to sample resistance on the trailer.

Starting at the trailer is the single biggest reason why a lot of people hate electrical problems they put the cart before the horse, follow the flow from the source back verifying that everything is in good working order and if not fixing along the way, somewhere you will find your problem.

Welcome to Electrical 101, next lesson costs Corona Extra...

 

[truckermatt]

Re: Chevy truck loses voltage at 50mph when towing boat

Well I fell sort of embarrassed here but oh well. I was looking over the trailer to double check every connection, and when i looked at the tail lights the were so loose that they almost fell off, Some how/some one loosened the mounting bolts and I bet that might have caused some issues at speed down the high way..

I check the lights before I leave each time when trailering and they all worked, but i didnt notice them being loose. So I tightened them up and will update when I tow again.

Its funny how sometimes things are so simple we skip over them.

 

[NHGuy]

Re: Chevy truck loses voltage at 50mph when towing boat

Oh yeah, keep it simple, silly. The polite version of the KISS principle. AKA, Keep It Simple Stupid.
I bet you found it.

 

[truckermatt]

Re: Chevy truck loses voltage at 50mph when towing boat

Well a quick update, I tightened all the trailer lights and towed again... And I was having the same problem..... So I went on a country road and with the lights unhooked. and it still happened. So now I know it is a problem on the truck side only when towing ... I am having the Alternator tested today, and the battery as well.

Hopefully just one is bad not both.

 

[MH Hawker]

Re: Chevy truck loses voltage at 50mph when towing boat

Yea it is funny how it works out with trailers, I recently made a good 200 mile tow with mine and I brought the boat home and went over things and noticed the license plate was bent, so I straighten it out and didn't think any more about it and at the first fuel stop walk around, I found a light housing cracked, apparently when I was loading the boat up it was a but close to the ramp wall and I hit it.:facepalm:

 

[matt167]

Re: Chevy truck loses voltage at 50mph when towing boat

get a volt meter and clip it directly to the battery as a test, and run the leads into the cab. You can use test leads as an extension, just tape them so there is no metal showing. Sometimes the gauges in that era of Chevy truck create ground issues and go erratic. Given the volt meter is read from the back of the board ( IIRC ). I would have to say a ground is starting to go faulty.

To go from 14 volts to below battery voltage in seconds the alternator would have to be shorted internally and at that point, it would get and smell very HOT.

 

[rbh]

Re: Chevy truck loses voltage at 50mph when towing boat

Biggest issue with DC gremlins I have found is dirty or loose conections.
If it only happens when you are on a bumpy road , odds are it is a loose and corroded conection.
Start with your battery and pull and clean the battery posts and cable connectors.
("do not" forget to wash and clean the top of the battery as the gunge that builds up there will short the posts out)

While your battery cables are off check the cables/wires on the back of the alternator for loose wires and corosion.
You can also visually inspect the wire looms/harness for rub points (Chafing), if you can see an area where the loom/harness bundle has been worn into the wires, that is a good place to look.

 

[truckermatt]

Re: Chevy truck loses voltage at 50mph when towing boat

Update,

i had the alternator and battery tested today, and they both test fine.. I figured that would happen since the problems only happens at 50 mph+ . I could try a new alternator, but I dont want to throw parts at it.

I will double check all the connections again...
Again this only happens when I am towing, but I "gunned" it last night w/o boat and the gauge fluctuated a little but now when I am towing.


The good and bad news is that winter is coming and I dont tow anything then, so I have a while to find the problem.

 

[LippCJ7]

Re: Chevy truck loses voltage at 50mph when towing boat

So have you procured a Digital Volt Ohm Meter yet? The next step is testing your power and ground connections, I suspect a bad wire or connection on the primary cables more then on the secondary cables since you are seeing such a dramatic drop in voltage. You dont state anywhere a smell of burning wire or and sparking, no blown fuses either so I bet your looking at a bad ground between the battery and the chassis ground.