Low beam voltage too low

chrysler
ptcruiser

#1

I just put away my old Honda Accord with almost 300,000 miles on it and picked up a 2006 Pt Cruiser for my daughter to drive at college.

While I was replacing third brake light, running light and a low beam headlight I couldn’t get the driver’s side low beam to light up. Eventually checked voltage and it’s just 11 volts. Anyone who’s ever looked under the hood of a PT Cruiser will understand that it’s a bit cramped in there. So, I’m looking for a way to rig the headlight.

Can I just tap the wire from the passenger side low beam to the driver’s side? Will that work or would that pull too much for either to work? The passenger side show 12.4 volts.

Thanks


#2

I wouldn’t. I suspect you may have a high resistance short-to-ground in the line feeding the subject light. You need to track that down and repair it.

Tot do this I recommend both a wiring diagram and a schematic. The wiring diagram shows you exactly where the wires physically run. Perhaps if you ask nicely you can get the parts window guy at the Honda dealer to print these for you for the headlight circuits.


#3

The Honda is gone and replaced by a PT Cruiser ( Chrysler product ) why the Honda was even mentioned just confuses people.

Even with only 11 volts it seems like there should be some light from the bulb but dim. Swap the bulbs and see what happens.


#4

Oops! The OP was clear, I just read the post with my Sunday-morning eyes… :dizzy_face:


#5

Do not expect the PT Cruiser to be as trouble free as the Honda… but maybe you are just starting to understand that right now!

I have a gearhead friend that put up with his wife and daughter’s desire to own PT Cruisers because they were “cute”. Serious problems with both of them caused him to swear off Chrysler products forever.

At least you’ll get to see your daughter regularly 'cause you’ll be chasing repairs on that PT until it totally fails or you dump it.


#6

I agree with @VOLVO_V70. 11 volts should be enough to light the lamp, although it won’t glow at full brilliance. I recommend you measure the voltage from the positive side of the headlight socket to the negative post on the battery. If you get 12.4 volts, the problem is where the light socket is grounded to the chassis or the negative terminal grounds to the chassis. To determine if it is the battery ground, it might be a good idea to check the voltage at another point. You might want to check the voltage across the battery posts to see if the battery is putting out 12 volts or higher. Your volt meter may also be giving a low reading.
My guess is that it probably is a bad ground. I had a similar problem with the right brake light and turning signal on my 1947 Pontiac. I had just installed turning signals and the right side didn’t work correctly (that was back when turning signals weren’t standard equipment). It turned out that the socket ground was bad. I also remember a 1955 Ford pulling into a filling station where I was hanging out as a teenager. One headlight was glowing faintly. The owner said that he had just replaced the headlight. The mechanic pulled out the headlight bulb and saw it was a 12 volt unit. The 1955 Ford had a 6 volt system.
Let’s not condemn the car because it’s a Chrysler product and not a Honda. For a car that is 11 years old, overall condition is more important than make.


#7

I don’t know details of automobile light bulbs, but I’d be surprised if you get near-zero light from 11 volts. (BTW, I presume you are measuring with the light bulb in place. If it’s 11 volts open circuit, then it’s whole 'nother problem.) That said, …

Rather than “high resistance short-to-ground in the line feeding the subject light”, more likely a high resistance connection in that line. Maybe you are very lucky, and the high resistance is just in the contacts of the relay that feeds that light. Try replacing the relay (swap with an identical one if the car happens to have it). If replacing/swapping works, try the old one again to see if the problem was in the socket, rather than in the relay’s internal contacts.

(If this light is fed from a separate fuse, try swapping that fuse to see if it has a “soft” failure or if its socket contacts are the problem.)

If it’s not the relay (or the fuse contacts), you will probably need the wiring diagram to follow “12V” from the battery, through the fuse box, up to the lamp socket. If you are lucky, the high resistance will be between contacts in a connector, and you can fix it just by unplugging and re-plugging the connector. If you are not lucky, the high resistance will be in a crimp connection or – ugh!! – a flaw in a connector or wire itself.

If the problem is a flaky connection that gets fixed by unplug and re-plug – the relay, fuse, or harness plugs – maybe put on a bit of dielectric grease on it.


#8

Power to the headlights is supplied thru the Totally Integrated Power Module.

This is a common problem on Chrysler vehicles.

Tester


#9

I suspect the 11V reading was with the bulb out.
A very high resistance in the wiring combined with a meter with a 1-10 megohm input impedance allowed the meter to read some voltage even though the wiring is essentially open.
With the bulb in place it probably gets only a few millivolts.


#10

I would first look at the socket, then work your way up the expense ladder.


#11

switch the bulbs around and measure again. If the voltage drop moves with the switch you have a bad bulb. A bad bulb can do magical things.


#12

that would blow the fuse


#13

Reading voltage has nothing to do with the impedance of a meter.

Impedance comes into play when reading resistance with a meter.

For example, if you were to test the resistance of a throttle position sensor, where the computer sends a reference voltage of 5 volts, using a digital meter that has a 10 mega-ohm impedance input would only send enough voltage thru the sensor to get a reading.

If you were to use an analog meter for the same test, where there is no input impedance, the meter would send the full 9 volts of the internal battery in the meter thru the component, frying the throttle position sensor.

Tester

.


#14

huh? no way. High impedance will not blow the fuse.


#15

not true. If the impedance of the source is high, as was postulated, then the voltage measured depends on the impedance of the meter.

“If you were to use an analog meter for the same test, where there is no input impedance, the meter would send the full 9 volts of the internal battery in the meter thru the component, frying the throttle position sensor.”

also totally wrong. First, an analog meter has significant input impedance, typically 20kΩ or higher. And second, the higher the meter impedance, the more accurate the measurement. Infinite impedance would have the least error, although 10MΩ is good enough for most cases.

And third, any internal battery is not in the circuit when measuring volts with an analog meter.


#16

You folks need to switch back to English for morons like me. Of concern to me is that totally integrated power module that Tester mentioned. Normally I believe the wiring for the second light would just be pigtailed off the first headlight. So the problem would have to be either the splice, wiring in between, on the socket. But does that power module change that? Remember that big problem with that caravan a year or so ago? Not something to fool with. So my question would be what connection that power module has to the second headlight wiring?

Pending the answer, I guess I would first swap lights to see if it might be the bulb. Then I’d start looking at the splices if there are any, the socket itself, and then the wiring between them. Nothing wrong with using alligator clips and a wire to test add a new ground or to run from one headlight to the other to try and isolate which wire if any.


#17

I will bet the ground for that light is bad. Bypass it with a new wire to a convenient spot on the body if that’s the case, rather than trying to repair it.


#18

Woah! This is the most active group I’ve ever posed a question on!

My daughter’s been off in the car all day, so I’ve not been able to test anything today, but I can answer some questions…

I tested all the fuses, they are good.

I swapped the left and right bulb and that didn’t solve it.

I got 11 volts on the light socket without a bulb in the socket.

I tested socket to battery and got 12 volts on the positive and got some voltage at some combination on the negative, which I read would subtract from the overall and explain the bulb not lighting up.

So I do believe it’s in the ground circuit. I’ll try to tap/run a new ground tomorrow and see if that helps and not just run a straight wire from the working light.

The wiring goes into a bundle about 6" from the socket and under a PT Cruiser hood is crazy crowded. I don’t think I can trace it to the source.

I’ll post back results.


#19

Reading voltage has nothing to do with the impedance of a meter.
No, impedance has EVERYTHING to do with the impedance of the meter. If the meter has no impedance it will have a dramatic effect on the measured voltage. If the meter’s impedance is infinite it will have zero effect on the voltage it measures.

Impedance comes into play when reading resistance with a meter.
Impedance is nothing but the word used to measure the “resistance” in non-AC circuits. Impedance incudes both DC resistance and reactance.

For example, if you were to test the resistance of a throttle position sensor, where the computer sends a reference voltage of 5 volts, using a digital meter that has a 10 mega-ohm impedance input would only send enough voltage thru the sensor to get a reading.

That 10 megohm impedance is used on the VOLTAGE measurement only.

If you were to use an analog meter for the same test, where there is no input impedance, the meter would send the full 9 volts of the internal battery in the meter thru the component, frying the throttle position sensor.

And the digital meter will also send the full 9 volts to the sensor, and that’s rarely enough to do any damage.


#20

per your comment it doesn’t matter where the 9V comes from, but you are saying that in one case (analog) the sensor would fry but using a digital sensor it would not. Does not make sense to me. What am I missing? 9V is 9V regardless of where it comes from.