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Old 06-03-2020, 08:35 PM   #1
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'93 Ford E350 - tailights and all running lights not working

Per the title, I have an older Class C on a 1993 Ford E350 chassis. Headlights, brake lights, front and rear turn signals all work, but I can't get the tail lights and all of the running/clearance lights working when the headlights are turned on.



I have checked all the fuses...


I'm assuming I have a break in the circuit somewhere, but not sure how to track it down.



Any advice? Thanks!


ryan
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Old 06-04-2020, 01:03 PM   #2
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Did some more checking this morning...went through all the fuses again with an ohmmeter and test light and I can't find any bad fuses. Pulled the rear tail lights and started checking the wiring. There are 2 bulbs in each light - one for the brake light and the turn signal light and another one for the tail lights. I have no voltage on the yellow wire that connects to the tail light. I have no wiring diagram for this coach as Cobra has been defunct for years.


I'm assuming that things start at the headlight switch and power runs from there back to the tail lights and from the tail lights it runs to the clearance lights. I have checked the ground wires at various places and I seem to have good grounds. Just not getting 12 volts to the yellow wire to the tail lights.
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Old 06-05-2020, 06:01 PM   #3
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The headlight switch could be the problem. Pull the switch out to the park position and check all of the lights
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Old 06-05-2020, 06:20 PM   #4
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Quote:
Originally Posted by rgnprof View Post
Per the title, I have an older Class C on a 1993 Ford E350 chassis. Headlights, brake lights, front and rear turn signals all work, but I can't get the tail lights and all of the running/clearance lights working when the headlights are turned on.



I have checked all the fuses...


I'm assuming I have a break in the circuit somewhere, but not sure how to track it down.



Any advice? Thanks!


ryan


I had the same problem once I replaced the bulbs all the way around it lit up like a Christmas tree...so I assume they are all on the same circuit and if ones out there all out...hope that helps a little
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Old 06-05-2020, 09:07 PM   #5
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I have checked every single bulb, pulled them all and even checked each light's wiring for continuity and I do not have a broken circuit. Everything seems to be grounded - I just have no 12 volts anywhere.



Checked the fuses again and I see no blown fuse...


I have wiggled and rotated the headlight switch 100 times - pull it out to first stop and the amber sidelights (beside the headlights come on, but that's it). Pull the switch out further and the headlights come on, but that's it - no tail lights and no clearance marker lights.


I hate things electrical!
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Old 06-06-2020, 05:31 AM   #6
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Hi rgnprof,

I believe your troubles are most likely related to the wiring that begins behind the rear axle, at the point where the outfitter attaches to the Ford wire harness.

Given your description, I would check the voltage again this way.

Run a very long wire directly from the chassis battery post ground. If that checks out good, switch the length of wire to the battery post 12V to provide 12V to your lights that way.

The first test would verify a good or bad ground.
The second test would verify a good or bad 12V.
In both cases you are checking the integrity of the wiring and sockets within each tail light.

Such trouble is most often caused from corroded "Crimped Connections" in the area of the tail lights. Lots of outfitters use crimp connections that over the years get corroded from dampness, water, and salt spray. Some outfitters wrap some electrical tape over the crimp, but it is not forever reliable. I would look under the rear bumper in the area looking for crimped connections behind the tail lights. Pending your rig's design, you might have to remove each tail light to find the crimps.

Do the following for each crimp found.

- cut off the crimp
- strip the wire ends
- use 0000 steel wool to get the strands clean for soldering
- slide a length of shrink tubing over the longest wire
- solder the wires together
- slip the shrink tubing over the area with 1/2" overlap on each end
- seal it by shrinking it with heat (a butane lighter for a grille works great for that)
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Old 06-06-2020, 02:02 PM   #7
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Thanks for the replies.



I have pulled the tail lights and checked all the connections (I changed out both tail lights last year, year before - and they were recrimped then. I even rewired a few yesterday using heat shrink crimped butt connectors.



Quote:
Run a very long wire directly from the chassis battery post ground. If that checks out good, switch the length of wire to the battery post 12V to provide 12V to your lights that way.

Ron - can you describe how to check the ground using this long wire? I think I know how to check the lights by wiring the hot wire to the wire I've identified as the tail light wire.


I'm not exactly sure where the "outfitter attaches to the Ford wire harness"... I know I'm looking for a yellow wire that connects to the tail lights and I found a bunch of wires underneath the coach and a connection in an interior compartment at the very rear of my coach on the driver's side - where my 30a connection comes out.
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Old 06-06-2020, 03:14 PM   #8
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Originally Posted by rgnprof View Post
Thanks for the replies.



I have pulled the tail lights and checked all the connections (I changed out both tail lights last year, year before - and they were recrimped then. I even rewired a few yesterday using heat shrink crimped butt connectors.


Ron - can you describe how to check the ground using this long wire? I think I know how to check the lights by wiring the hot wire to the wire I've identified as the tail light wire.


I'm not exactly sure where the "outfitter attaches to the Ford wire harness"... I know I'm looking for a yellow wire that connects to the tail lights and I found a bunch of wires underneath the coach and a connection in an interior compartment at the very rear of my coach on the driver's side - where my 30a connection comes out.
If you're not getting running lights at the front or back, then isolate your diagnosis the headlight switch first.

You should be able to backprobe the connector on the back of the switch and see if you get voltage out in the running light position.

Verify this first before doing anything else.

Expanding a bit here in edit, the wire coming out of the switch that runs to the lights should be be brown and the incoming power for the running lights should be tan/white.

If you did recent work on the lights did you use the proper wattage bulbs? Higher wattage bulbs can cause too much current draw.

At any rate, regardless of what you did, it's common for the pins on the switch and connector to lose connection over time and get damaged from the heat caused by the poor connection.

Start at the switch and work back.
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Old 06-06-2020, 04:19 PM   #9
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Originally Posted by checkthisout View Post
If you're not getting running lights at the front or back, then isolate your diagnosis the headlight switch first.

You should be able to backprobe the connector on the back of the switch and see if you get voltage out in the running light position.

Verify this first before doing anything else.

Expanding a bit here in edit, the wire coming out of the switch that runs to the lights should be be brown and the incoming power for the running lights should be tan/white.

If you did recent work on the lights did you use the proper wattage bulbs? Higher wattage bulbs can cause too much current draw.

At any rate, regardless of what you did, it's common for the pins on the switch and connector to lose connection over time and get damaged from the heat caused by the poor connection.

Start at the switch and work back.
Oh my bad. Didn't see you were in fact getting front (chassis) parking lights.

Disregard.
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Old 06-06-2020, 05:59 PM   #10
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Just to make sure - if I'm getting power to the amber colored parking lights located next to the headlights when I pull the headlight switch out to the first stop - THEN it can't be a bad switch.


Right?



Which makes sense to me - clearly if I'm getting power at the first stop of the switch to the front parking lights only then I should be getting power from the switch to the other lights (tail, clearance). Ergo, I have a break somewhere after the switch!


ryan
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Old 06-06-2020, 07:28 PM   #11
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Just to make sure - if I'm getting power to the amber colored parking lights located next to the headlights when I pull the headlight switch out to the first stop - THEN it can't be a bad switch.


Right?



Which makes sense to me - clearly if I'm getting power at the first stop of the switch to the front parking lights only then I should be getting power from the switch to the other lights (tail, clearance). Ergo, I have a break somewhere after the switch!


ryan
Correct. There might be a relay box that is part of the coach since the amp draw of the extra clearance lights is much higher than what the vehicle wiring may have been sized for.

Is there a 12v fuse box (separate from the converter/charger) and separate from the ford chassis box anywhere in/under the coach? Maybe in a side compartment?

Do you by any chance have a trailer plug? Check for running light power there if you do.
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Old 06-06-2020, 07:47 PM   #12
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Quote:
Is there a 12v fuse box (separate from the converter/charger) and separate from the ford chassis box anywhere in/under the coach? Maybe in a side compartment?

I haven't run across one, but I will look better...
As far as the trailer plug, I do tow a Subaru and the electrical connection is basically 4 wires. I checked all the wires for voltage and they all seem to be working fine, including the tail lights. I connected these myself years ago using a Blue Ox lighting kit where I installed an extra bulb in the Subaru tail light/brake light housing. I tested for voltage with my meter and I have 12 volts through the pigtail with the motorhome headlights on...so basically, with the headlights on I have no motorhome tail lights but I do have toad tail lights.
Any of that make sense?
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Old 06-07-2020, 05:43 AM   #13
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I changed out both tail lights last year, year before - and they were recrimped then. I even rewired a few yesterday using heat shrink crimped butt connectors.

Ron - can you describe how to check the ground using this long wire? I think I know how to check the lights by wiring the hot wire to the wire I've identified as the tail light wire.


I'm not exactly sure where the "outfitter attaches to the Ford wire harness"... I know I'm looking for a yellow wire that connects to the tail lights and I found a bunch of wires underneath the coach and a connection in an interior compartment at the very rear of my coach on the driver's side - where my 30a connection comes out.
About recrimping to original wiring.
If the strands of the original cut wire that you crimped to were discolored, your recent crimped connections are likely giving you the trouble.

About verifying a good ground.
Just for testing purposes, run an independent ground wire from the chassis battery to the tail lights, connecting it to the ground on one of the tail lights. It was common practice in older rigs, the metal housing of the tail light is the ground. If that is your case, alligator-clip the test ground wire to either tail light housing.....assuming it is metal, not plastic. Make sure to attach to clean bare metal for the test. A poor ground is a common problem created from corrosion.

Regarding where the Ford wiring stops and the outfitter wiring starts.
You have a 27 year old rig so I am not certain Ford practiced this back then. But Ford ships it's cab & chassis to outfitters, terminating the tail light wiring at a connector located in the area of the rear axle, and capped for protection. Ford also supplies a length of wire harness with the mating connector for outfitters to work with from that point. So your crimped tail light connections would likely attach directly to the ends of the Ford-supplied wire harness, or very close to it near the trailer hitch wiring. I believe one Ford-to-Ford wire harness connection by the rear axle, supports both the tail lights and trailer hitch wiring.
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Old 06-07-2020, 10:27 AM   #14
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I haven't run across one, but I will look better...
As far as the trailer plug, I do tow a Subaru and the electrical connection is basically 4 wires. I checked all the wires for voltage and they all seem to be working fine, including the tail lights. I connected these myself years ago using a Blue Ox lighting kit where I installed an extra bulb in the Subaru tail light/brake light housing. I tested for voltage with my meter and I have 12 volts through the pigtail with the motorhome headlights on...so basically, with the headlights on I have no motorhome tail lights but I do have toad tail lights.
Any of that make sense?
So, point being, if you're getting running light power to the trailer connector, then your problem is at the back of the coach after where ever you wired the tail/running lights into the motorhome light wiring.

For clarification, are you getting toad tailights when your motorhome headlight switch is in the headlight position or the running light position or both?

Again though, some vehicles have isolated trailer light circuits that work off relays so the vehicle's original wiring isn't overloaded.
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