HELP ! Lights not working.

[m37jarhead]

The headlights, tail lights and brake lights suddenly quit working.
The turn signals work fine, as do the four-ways, dash lights and gauges.
The second breaker keeps tripping. It's the 2nd breaker forward of the gauge panel.

I momentarily hot wired around the breaker, with a 10 amp fuse in line for safety, but still no lights.
And the 10 amp fuse did not blow.
Re-connected the breaker and then disconnected both headlights and both tail lights,
thinking there might be a dead short in line there.
Nothing changes, breaker still trips. I get no voltage to any of the lights. Batteries shows 24V ++.

Front and rear harnesses are all new fron Vintage Wiring and WERE working fine until recently.
I have several wiring diagrams, multi-meters and test lights.

Any thoughts on how to diagnose this problem??

Jerry

[w30bob]

Jerry,

From what you're saying it sounds like the problem is in the light switch. Without a diagram of YOUR wiring it's going to be a little difficult to diagnose. Did your truck have directionals or were they added with the new harnesses? Which light switch are you using (early single connector or later dual connector)? The second breaker (it's position could have moved over the years) has the #15 wire feeding the light switch. If you're bypassing the breaker and still not getting your lights to work I'd suspect the switch. Check to verify you have 24V going into the switch with the breaker bypassed. If you do then bypass the switch to verify the lights work. If all works, then the only thing left is the switch. I assume you have the correct breakers (15A) installed?

regards,
bob

[ashyers]

Check your brake light switch for a short to ground, mine did it this summer, intermittent, then completely.

[just me]

Bring it by my place and we can troubleshoot it end to end. Or to our shop in mesa. That is where all my Douglas stuff is along with spare switches. ( not going to mtg tonight. Have to be at work at 0500)

[just me]

I busted a light switch open and there was a breaker and 2 resistors in it.
Plug it all in and turn it on. When the breaker trips, if you still have power on 15, it is the breaker in the light switch.
Try hitting the dimmer once and see it the lights don't work. On my truck, the clutch pedal hit the wire for the dimmer (18) and shorted it. Switching to high beam cleared it. Moved and reinsulated the wire and all has been fine.

[m37jarhead]

Good advice from all of you guys.
I'll dig into the light switch problem tomorrow.

Bob, as I remember, on the hot wire from the switch to the breaker, I got 24V.
It must be or it wouldn't trip the breaker behind the gauge panel.
Will recheck that again tomorrow and run a hot wire off the connector on the
light switch to the breaker and/or the headlights.

More tomorrow............
Thanks all.....
Jerry

[m37jarhead]

Jerry,

From what you're saying it sounds like the problem is in the light switch. Without a diagram of YOUR wiring it's going to be a little difficult to diagnose. Did your truck have directionals or were they added with the new harnesses? Which light switch are you using (early single connector or later dual connector)? The second breaker (it's position could have moved over the years) has the #15 wire feeding the light switch. If you're bypassing the breaker and still not getting your lights to work I'd suspect the switch. Check to verify you have 24V going into the switch with the breaker bypassed. If you do then bypass the switch to verify the lights work. If all works, then the only thing left is the switch. I assume you have the correct breakers (15A) installed?

regards,
bob

Bob:
1. Yes the truck had turn signals before the new wiring. Still has turn signals and they are working.
2. Light switch has just ONE screw-on, 12 pin connect.
3. Also will ck #15 wire to see if it's hot and ck for correct 15 amp breaker.
#15 wire goes to the "F" pin on my diagram.
4. FYI... all the panel lights work.
Jerry

[m37jarhead]

Check your brake light switch for a short to ground, mine did it this summer, intermittent, then completely.

Good tip. Will check brake light switch today.
Jerry

[m37jarhead]

I busted a light switch open and there was a breaker and 2 resistors in it.
Plug it all in and turn it on. When the breaker trips, if you still have power on 15, it is the breaker in the light switch.
Try hitting the dimmer once and see it the lights don't work. On my truck, the clutch pedal hit the wire for the dimmer (18) and shorted it. Switching to high beam cleared it. Moved and reinsulated the wire and all has been fine.

I have tried hitting the dimmer switch from hi to low. Nothing so far.
I will hot wire across the dimmer switch today.
Thanks,
Jerry

[m37jarhead]

UPDATE: 3/4/16
I borrowed another light switch for testing.
Same issues... no head lights, no tail lights.
Still "pings" the breaker.
Hot wired terminal "F" to terminal "H" on the plug end of the harness
that goes to the light switch.
Good thing I put an in-line fuse in the hot wire. F to H repeatedly
blew the in-line 15 amp fuse. Also hot wired F to all the other alpha
terminals. Did not blow any fuses on those.
"H" is wire #21, service tail lamp.

Jerry

[carolinamv]

Did the brake light switch fix it? Mine did the same thing until I fixed it with a new switch.

[m37jarhead]

Did the brake light switch fix it? Mine did the same thing until I fixed it with a new switch.

Jay:

Brake light switches are cheap. I'll try a new one.
Thanks,
Jerry

[RMS]

Brake light switches are cheap. I'll try a new one

or pull the wires and eliminate the suspect switch.

my first suspect would be just after the joining of 17c and 17b on the hi/lo switch. the hi lo switch has two fixed connectors and a short pig tail that could have shed its insulation.

next I would look for a rub through like 15 crossing the steering column support bracket and the turn signal wires depending on routing.

if its a civilian turn signal that lights up the wires to those light would be suspect

[m37jarhead]

I put a different brake light switch in line....... no change. Breaker still pops.

RMS: Tomorrow I will check wire 17c and b for insulation breaks. Will also check 16 while there. thanks.
Jerry

[m37jarhead]

Brake light switches are cheap. I'll try a new one

or pull the wires and eliminate the suspect switch.

my first suspect would be just after the joining of 17c and 17b on the hi/lo switch. the hi lo switch has two fixed connectors and a short pig tail that could have shed its insulation.

next I would look for a rub through like 15 crossing the steering column support bracket and the turn signal wires depending on routing.

if its a civilian turn signal that lights up the wires to those light would be suspect

UPDATE !! 3/22/16
I traced wire #21 out of the back of the light switch plug and thru the fire wall. I have checked all those Douglas connections before. This time saw 21 had burn marks at the Douglas connection on the right inner fender well.
The rubber collar/insulation had failed causing a dead short from 21 wire to the metal ring holding the rubber collar
and to the Douglas shell to clip on the fender well.

Repaired that and now the headlights, hi and low, and tail lights work. Breaker no longer pops. Military turn signals were never affected. Still working on brake lights. Changing to a NOS brake light switch did not change anything. Hot wired around the switch.... no change. Have 24V hot wired around the switch but no voltage to the brake light wires at the rear. More testing today. Will closely eyeball #15. (Thanks RMS for that tip.)

Closer inspection of other Douglas connections revealed many of the rubber collar/insulators were cracked, split and missing chunks of rubber clearly exposing bare wires.
The front and rear harnesses are fairly new from Vintage Wiring. I'm more than just a little disappointed with the insulators failing. I emailed Joe at Vintage Wiring for clues on the failures and replacement insulators.

These failing insulators are surely a fire waiting to happen. #@%$# !!
I only picked Douglas connectors because they were original to my truck. Now with 20/20 hindsight I would have
ordered Packard connectors. Hoping my M37 will not turn into an expensive marshmellow roast. Master cut-off
switch installation is in the VERY near future.

Many thanks to w30bob and all others for the help.
Jerry