1939 LaSalle VERY Dim Lighting

[jamesmadconductor]

I'm looking for some suggestions/experience/advice to begin addressing some electrical concerns I have on my 39-5019.

The headlights were converted to sealed beam, much to my dismay, but it appears that the only change is inside of the headlight buckets, and that the new wiring meets original at the terminal block, just inside the engine compartment on both sides. The sealed beam units are correct 6V bulbs, but when I run a meter across them, I'm getting about 2.5V on low beam, and 3.5-4V on high beam. This makes the vehicle very unsafe for night driving. In addition to the headlights, all the lighting appears to be very dim overall, especially instrument lights.

My first thought was bad ground, but I ran a direct ground from the headlight wiring to the battery and there was no change. Behind the dash, the harness is entirely original, with only a 6V aftermarket turn signal addition. Some of the original wiring is a bit frayed, but appears to be in overall ok condition.

Is it possible to see such a big voltage drop from a failing headlight switch? Has anyone here experienced a similar issue and found any solutions?

Any help or guidance is greatly appreciated. I try to drive the vehicle at least every other day, but the lighting has me concerned.

Regards,
James

[Jeff Rosansky CLC #28373]

I would remove all wiring in that circuit and clean the terminals. What is the voltage coming out of the switch?
I would also check the voltage going to the switch as well because the problem could be before the switch and then you would just be chasing your tail. Contacts in the switch are probably corroded. If the switch hasn't been used often then I would exercise it to try to clean them up.
Jeff

[bcroe]

If you just start changing stuff without FIRST identifying the fault,
you might accidentally make it go away, only to return later.  Or
there may actually be multiple problems. 

I would suggest using a good meter to walk around the circuit,
to find the exact fault or faults.  Tie one lead (with a perhaps
long lead, no voltage loss for a voltmeter) directly to the battery
positive, and walk the other lead down the current path to the
operating headlight.  The total drop should best be kept below
1/4 volt, but as you cross the fault, there will be a big voltage
increase.  A ground fault is less likely, but continue around the
path back to the battery.  The voltage at the headlight grounded
terminal should be within 1/10 volt of the voltage back at the
battery. 

Once the area of the fault is identified, use the meter to find
the exact spot.  It could be a combination of battery grounds,
inadequate power wiring, and the switch (the meter tells all). 
Bruce Roe  CLC # 14630

[Steve Passmore]

My first port of call would be the 'Thermostrip' and Points on the back of the light switch. They can become corroded.

[fishnjim]

If you just measure voltage across the two prongs, you're not reading anything meaningful, unless you have those values from when the light was good.   Disconnect the light bulb and check the voltage at the socket to ground.  If it's significantly different than what's at the battery then there's a fault in the circuit.   
Check the ohms to ground from the socket(neg), should not be much, <1.
   
This is common in the 6v pos grnd systems.   A little bit of loss means a lot.   Doesn't take much to burn up some wires causing more resistance.   They have to pass twice as much current as a 12V to get the same wattage, which takes a larger wire size.   So make sure the new wires are the proper gauge, should be around 12 GA.   I don't know if the wiring diagram for that year gives the gauge.  If not, measure one of the original wire diameters and convert from a chart.  Wire gauges changed over the year with metirfication, so new maybe different than original.

[bcroe]

If you disconnect the bulb, the voltages won't tell you anything,
because the current flow is what causes the voltage drop. 

OK so I said start with a V meter wire on the battery positive,
forgetting this car has positive ground.  So starting with the HOT
terminal (neg on this car) walk around the circuit with the other
wire, though either point would eventually get you there. 

Bruce Roe

[las39]

I'll try to give some advice with the best of my English.

You mentioned you tried extra grounding with no effect, which means your problem is with your "warm" end (minus) trough switch, wiring terminals on inner fender foot switch (high beam) and so on as mentioned by the others.
You don't mention your battery voltage. You need to know when measuring voltage drop.

Try to connect a lead from minus to the light switch feed terminal that comes from the ammeter? If there is a difference then it's the switch.
If no difference, try and connect the lead on the other side of the ammeter, where it feeds from battery.
Also feed the bulb directly, is it really a 6 volt ?
I have attached a colored diagram, the colors are random for clarification. 

[bcroe]

Of course lamp voltage cannot be good if battery voltage is bad. 

That diagram should make it easy to trace.  With a meter lead
connected to the hot (-) battery terminal, and the lights on, move
the other probe down to the hot side of the AMMETER.  It should
read no more than a couple dozen millivolts.  Moving to the output
side of the AMMETER might show a few dozen more; I think the
voltage drop across the AMMETER should not exceed 50 millivolts. 

Move to the THERMOSTATIC RELAY, total voltage drop should be
under 100 mv.  Looks like headlight current comes out of terminal
11, again expect minimal increase in voltage drop.  Moving to the
FOOT SWITCH, expect minimal mv additional drop to the center
terminal, and to 1 or 2 that is selected.  From there follow out a wire
to a headlight, again seeing mv level increases in drop along the way. 

Most likely there will be found a huge shift of volts level along the path,
narrow in on this, your problem.  Once repaired, a recheck might
reveal another weak link needing repair.  I would not hesitate to
replace a wire with a heavier wire if needed. 

The same method works from the battery ground (+) tracing to the
headlight ground, much simpler.  good luck, Bruce Roe

[39LaSalleDriver]

Following this with interest as I have discovered (after getting my other electrical problem solved) that my 39 Lasalle is doing the exact same thing.

Headlights flat out quit after about 5 minutes, and the add on ammeter starts bouncing around wildly. Turn them off and a few minutes later, turn them on and they work again for a few minutes.

I'm thinking it is "points" on the lighting system that may be causing the problem.

[Janousek]

You might want to add a headlight relay hidden under the dash.  This will make an old switch usable again and send more voltage to the headlights than the factory switch ever could.  A reliable upgrade to the system and since you have to tap battery power you can ad a hidden fuse for the headlight circuit. 

[Steve Passmore]

Following this with interest as I have discovered (after getting my other electrical problem solved) that my 39 Lasalle is doing the exact same thing.

Headlights flat out quit after about 5 minutes, and the add on ammeter starts bouncing around wildly. Turn them off and a few minutes later, turn them on and they work again for a few minutes.

I'm thinking it is "points" on the lighting system that may be causing the problem.

I would put money on you being correct. I have experienced it several times. Sometimes it's a short in the system but in the cases I have seen the points become dirty and don't make a good contact or the thermal strip is rusty and weaker because of its age and separates the points at a lower temperature. It's easy to bypass it altogether and fit an inline fuse as long as it is definitely not a short.

[bcroe]

A relay can solve a few problems.  The most effective physical
location is between the battery connection and the headlights. 
I would run a properly selected fuseable link from the battery,
which generally will be more reliable and have less voltage drop. 

Bruce Roe

[39LaSalleDriver]

With a setup like this, I'm surprised I have any headlights at all.    

Going to rewire the whole mess with 12 ga wire, new sockets, and install 40 amp self resetting circuit breakers. I assume I'll need four (one for hi and low both sides). Should I install them in the headlight buckets? Any other recommendations?

[stevehayes]

Well, whenever I need an electric service provider I appeal to this company https://bates-electric.com/locations/st-louis-mo/. Honestly, I am not sure that they provide electric service for cars, but if you want you can ask them. Unfortunately, the house I bought a few years ago is pretty problematic and the most often problem I meet is related to electricity. It has a lot of troubles with the electricity and if there was not the company I mentioned above me life would be far worse, so I am really grateful to them for all they have done, and for their professionalism.

[Bobby B]

Well, whenever I need an electric service provider I appeal to this company https://bates-electric.com/locations/st-louis-mo/. Honestly, I am not sure that they provide electric service for cars, but if you want you can ask them. Unfortunately, the house I bought a few years ago is pretty problematic and the most often problem I meet is related to electricity. It has a lot of troubles with the electricity and if there was not the company I mentioned above me life would be far worse, so I am really grateful to them for all they have done, and for their professionalism.

Steve,
Hi. Not for Nothing, but 7 out of your 8 previous posts have nothing to do with Cadillacs or Cars in General. You're plugging other companies on a Cadillac Forum, which are unrelated to anything going on here. What's up with that?
                                                            Bobby

[wheikkila]

Hi Steve
Be sure to check the dimmer switch. All your headlight power goes through it. I had a lot of issues with my 40 Lasalle till I replaced the dimmer switch.
Thanks Wayne