Lighting Help

WayneR · #1 11-06-12, 15:40

I am having problems with the headlights on my 71 M38A1 CDN3. Everything is working fine but I have no low beams on the headlights. I have changed the light cluster with 3 or 4 new ones as well as the dimmer switch on the floor. All the wiring looks good and the headlights are new. Any help or ideas will be greatly appreciated.

Thanks in advance

Wayne

Phil Waterman · #2 11-06-12, 16:48

Hi Wayne

First diagnostic question, did you have low beams before this problem?

Or is the beginning of the problem unknown?

I'm in the midst installing the head lights on my HUP and a similar problem high beam no low beam. Which was actually caused by two different problems power to the wrong terminal on the dimmer switch and open ground.

Cheers Phil

WayneR · #3 11-06-12, 17:48

Hi Phil

This was existing when I picked up the jeep. Orriginally I was told it was a light cluster issue but after replacing it several times I am trying other avenues.

I will look at all the groundings as well as the wiring on the dimmer switch.

Thanks for the information.

Wayne

Phil Waterman · #4 12-06-12, 01:16

Hi Wayne

I suspected that this was an existing condition, also suspect that you will find that it may well be a incorrect connection I'd start at the dimmer switch. Do you have a wiring diagram to check the connection of what goes where?

There are I believe three wires coming to dimmer switch if so it will basically light the bulbs on either high beam or low no matter how you connect the wires.

Dimmer switch should have one connection marked as power or bat this should be getting power from the light switch. The other two terminals are for the high and low.

As I said just went through this with my HUP.

Cheers Phil

SteveJ · #5 12-06-12, 03:30

The dimmer swithch is where I would go. Had a similar event on a friends M38 and the wires to the switch were on the wrong terminals.

rob love · #6 12-06-12, 05:31

Wires no 17 and 18 are for the low and high beam on the headlights. Wire no 91 at the headlights is ground. Make sure the headlamps are wired correctly and then check for continuity from the terminal at the hi/lo switch to the wires at the headlamp.

At the hi/lo switch, you will notice that one of the three holes is ribbed on the outside. This is the hole where the power (hot wire) should go into.

Unrelated to your problem, but it was common for the drivers to cross the wires at the headlamps during replacement of a bulb. If a headlamp wire no 91 is not wired to ground, you end up with a very dim headlamp bulb and a hi beam indicator lamp that will not go out completely on low beam.

Frank v R · #7 12-06-12, 22:50

Did you install the seal beams or did they come with the vehicle ? DND had a whole batch of seal beams new in the box from GE that were bad , they came in the blue and yellow boxes , most did not work or blew almost instantly , other wise check your wiring , by the numbers, hope this helps,
Frank

Stan Leschert · #8 13-06-12, 07:19

Get out your multi meter, and check the bulbs first. Then start at the beginning of the circuit and keep going until you find where you have no power. Report back, and we might be able to tell you more, unless you find it yourself. Report back anyways.

chris vickery · #9 13-06-12, 14:33

I recently had an electrical issue with my 1970 CDN3.
I had no RH turn sig front or back. As I dove into it further I ended up with no sigs at all. It turned out to be two issues working with each other, like an electrical gang fight...
What I discovered after indepth diagnostics was that
1) the RH front sig wire was going to ground because of old insulation (shorting)
2) the sigs problems began in the turn signal switch. A NOS replacement cured the problem. These use a solid state board that was cooked.
As much as electrical issues are a headache, if you start with the basic and work from there it is usually not too hard to pin point the issue.
Break it down to individual components and circuits. A multi check on bulbs for continuity to ensure operating condition. A check on the circuit from point A to point B for continuity. Check your switch for operation on the high and low to ground. Check for connections being the correct ones as previously mentioned. NOS or new components are often times defective right from new.

WayneR · #10 18-06-12, 15:44

It turns out the number 18 wire has no continuity. I tried to by pass with a new wire but that didn't work either. Do I have to now change the entire wire harness or is there an easier fix?

Wayne

Casey B · #11 19-06-12, 03:37

search for the break in the wire..its probably pinched or it broke at a joint through the fire wall? shorted at the gromet? maybe the pin is off the end at the connector> keep testing with a shapt line teaser from one end till you do not get power...then you know where the break is...use an ohm meter or a bulb and a battery and just use one end of the circuit using the wire and follow the wire using a sharp in etc to go through the wires inulation to get the bulb to light when you have gone past a point where the bulb no longer lights...the break is there between where you last tested and the place before.
Hope that helps! Oh is the switch for the lights to the head light position? not just driving or black out light? position..the three handled switch? some times if you click that switch off and on a few times the comtacts clean off a little for a cureent to pass through. check the switch on the dash.
Good luck and let us know.

rob love · #12 19-06-12, 04:44

Wayne: Bypassing the wire should have worked *UNLESS* if the wire with no continuity had a ground, it may have damaged the contact in the hi-lo beam switch. Check for power coming from the switch at the "18" plug. If you have power there, then a jumper wire from there to #18 on your headlights should result in light unless your lo beams on the lights are burnt out.

Chris:
The description you give is typical of the results of a short to ground on any one of the turn signal wires. The first symptom will be that the indicator light will not flash when you are signaling a turn, but rather will stay on steady. If caught early, the solid state flasher can be saved, but if left for a while it will be fatal to the flasher. I have also seen points in the control arm burnt as well. There was a modification on the M151A2 family to prevent some of this: an inline fuse was installed in the main power wire into the turn signals.