Good morning.

I have 2 problems with my truck which could be related:
1 - Headlight intensity fluctuating
2 - Guage occasionally jumping up to 18 volts

The reason I believe that these problems are connected is that in the mornings when going to work, the guage reads OK just to the right of centre and I am using the headlights. In the afternoon, when not using the headlights, after a period of time the guage slowly creeps up to 18 volts and sometimes comes back to normal and again after 5 to 10 minutes jumps to 18 volts.

If the alternator would go up to 18 volts as soon as the truck were started and stay there, I would definately suspect the alternator voltage regulator. But this intermittent faulty has me going up the wall.

I have read some threads about problems being encountered with the headlight switch which I intend to inspect later today.

Any help would be appreciated.

 

put a volt tester across the battery terminals to confirm voltage when it goes up, if it is over 16, you will blow light bulbs and associated loads, regulator is bad, replace the alternator

 

Good morning.

Interesting readings with the voltmeter. I shall have to try confirm these readings. With the check guage light on and the guage indicating 18 volts, the reading on the drivers side battery was 12.67 volts and on the passenger side battery 14.71 volts.

 

I would load test that DS battery next.

 

Good afternoon.

Drivers side battery load tested, not pristeen but still indicates slightly in the green.

 

If you are relying on the dashboard gauge, I wouldn't worry too much, it isn't that accurate.

It sounds like your grid heaters are cycling and causing the dimming in the headlights...

When replacing batteries, it is wise to replace both at the same time or you will end up killing your new one.

 

Good afternoon.

It is not the grid heaters cycling. In the mornings when I am on the highway, I can see the lights dim. It is almost like they are going onto high beams and then off again when going over a bump or turning on the sgnalk light.

I wiill not be replacing any batteries until I have this voltage problem sorted out.

 

If there is a voltage difference between the two batteries at any given time, while they are both still connected to the vehicle, the problem is almost certainly a bad connection. Even if there is a battery defect causing a big difference in voltage between the two batteries, it should average out with them being hooked in parallel. Remove the cables from the batteries, clean up the connections, and have a real close look for resistance. The problem could also be where either battery negative cable attaches to the engine block.

 

Thanks for the information.

I will be going under the vehicle tomorrow to replace the starter positive cable and then I can also check the negative grounds.

Best regards

 

What he said, good info...

 

could also be the batteries...
what to voltages measure with the + terminal is removed from the passenger battery...same readings ? sounds like the driveside battery died..the passenger is ok..replace both..if the cables are ok..

-dkenny

 

The batterys are in parallel and as such should read the same unless there is a cable problem. Not to say the batterys can't be bad, but in parallel they must read the same voltage regardless of condition unless there is a wiring problem.

 

Good evening.

Replaced the drivers side positive cable leading to the starting motor. All other cables visually inspected and looked OK.

Started up vehicle and both batteries measured 14.56 volts.

Took for couple of test drives and no problems encountered with the voltage guage.

Quite possibly the all the other connections to the cable terminal caused the problem.

Many thanks for all the assistance provided.