Tow Light Wiring Problem

[CVD]

Short question - any suggestions on where to start looking for current disruption that occurs when the headlights are on?

Long version - After several years of flat towing the jeep with magnetic STT lights on the bumper, I’ve now have some sort of circuit disruption. Turning on the coach headlights or running lights, causes the jeep STT lights to no longer function correctly (or at all).

With coach lights off (daytime),
Brake – ok
Left or Right – both ok

With coach lights on (full on or running lights only)
Running lights – OK (but they seem dim, hard to tell in daylight)
Brake – nothing
Left or Right – slight flicker in both sides at same time

I’ve taken apart the tow wire receptacle at the back of the coach (by the bumper), all wires were tight.

I’ve put a test light/prongs in that receptacle at the back, got similar results – good signals with the headlights off, no signals with the headlights on.

Suggestions?

[jhilley]

It sounds like the umbilical cord is the common problem. Likely a loose set screw in either the plug or the jack. Can you plug the lights directly into the jack on the motor home?

[CVD]

jhilley wrote:
The problem is in the ground side of the magnetic tow lights. Take them apart and check for a borken wire to the ground side of the lamp (the base). Could also be caused by corrosion. Check all connections and clean the sockets.

TexasH wrote:

Tinyandthegang wrote:
The problem is not in your coach but in the ground to the toad lighting.

.

Check the ground wire at the plug to the coach. All the symptoms point to a bad ground on your magnetic lights. Also, you might check by rigging a separate ground wire from the ground wire on your tow lights directly to coach chassis. I would spice in a test wire near the lights themselves and run to the coach just to eliminate an internal break in the wire. The wiring on those magnetic lights take a beating. Just some other suggestions to try....

I have a 2'd set of magnetic tow lights; that give the same problems. Doesn’t seem likely it’s the light wiring. Maybe it's the umbilical cord (it looks good, no cuts in insulation). I do drive washboard dirt roads for a couple miles most trips, lots of shaking and dust back there.

As suggested, I'll try a separate ground wire, directly from the lights to the coach chassis frame - but can't get to it until next weekend. Thanks for the suggestions. I'll give an update in a week or so.

[jhilley]

The problem is in the ground side of the magnetic tow lights. Take them apart and check for a borken wire to the ground side of the lamp (the base). Could also be caused by corrosion. Check all connections and clean the sockets.

[TexasH]

Tinyandthegang wrote:
The problem is not in your coach but in the ground to the toad lighting.

.

Check the ground wire at the plug to the coach. All the symptoms point to a bad ground on your magnetic lights. Also, you might check by rigging a separate ground wire from the ground wire on your tow lights directly to coach chassis. I would spice in a test wire near the lights themselves and run to the coach just to eliminate an internal break in the wire. The wiring on those magnetic lights take a beating. Just some other suggestions to try....

[CVD]

There is no toad ground for these lights; no connection to the toad electrical systems at all. These are magnetic tow lights, that sit on the rear bumper of the toad (the simplest type of towing lights – or so I thought).

[Tinyandthegang]

The problem is not in your coach but in the ground to the toad lighting.

[CVD]

Thanks for the suggestions. Sounds like a loose or missing ground in my coach lights is somehow causing my toad circuit to not function properly (as explained by Kirk and Wa8yxm). I’ve investigated several ideas, no luck so far.

Given the issue occurs only when the running lights are on (including running lights and head lights), I assumed it was in the coach running light circuit (not the head lights). I looked at the coach STT housings, noticed if I wiggled the ground (green) wire while the running lights were on, the bulb would flicker. I replaced the entire STT light on both sides, thinking a loose bulb socket was the problem (only $12- each, worth a try). No change in symptoms.

I then crawled underneath, looking at the main wires from the battery. I traced them to where the heavy strap grounded the frame to the engine, plus I found a couple smaller ground wires screwed into the frame. All were tight. Plus, it seems like any looseness there would show up in the coach systems. Everything in the coach works properly.

I have a 2’d set of magnetic Toad lights. Same problem with them (so I don’t think those wires are the problem).

I then remembered one of my headlights has moisture inside (still worked, has been this way for years.) I took the head light completely out(no rust at all on the socket). No change in symptoms. I looked at and wiggled the other 3 headlights sockets, no rust or looseness.

I have approx. 12 running lights spread around the coach (like most class A’s). Do I need to start taking every one of them apart and try to trace the ground wire? Most are up in/near the roof, not sure how easy the wires will be to trace.

Any other suggestions?

[Kirk]

You have a bad or missing ground and the turn signals and brake lights are returning to ground through the entitlements of the running lights. Turning those lights on blocks that path. Start by checking for a good ground via the plug from the motorhome.

[wny_pat1]

Sounds like a bad ground. Pull your sockets and plug apart and look for a loose connection, or connections. You might be able to find it by using a test light first.

[wa8yxm]

Sounds like a classic ground fault.. Possible locations are the sockets in the lights themselves the wires to the plug, the socket or #1 with a screwdriver is the connection to the motor home chassis from said socket.

When I got my towed and had the LP-1 Lube pump installed the kit included a tow light system, the Add-a-lamp type where they put a 2nd bulb in the tail light housing,, I actually like that system when it fits as it does on my car.

Electrially... IT is the same as what you have.

Well, suddenly I had issues when I had the headlights on or some other times, Appeared to be a feedback between the tail light and the turn signal/brake light

I up-graded the groun on the SOCKET on the motor home.. And that fixed it.

I also had a problem like that with no towed some time ago.. That was a FRONT turn signal.. Never saw that one coming.

[cableguy574]

sounds like a loose ground

[Dadio24]

IMO it sounds as if you have stray voltage crossing over to a ground wire causing line loss, causing the dimming, flicker is voltage/shorting causing the voltage to ride the ground wires. These are hard to find. I real good technicians may be able to help within a few minutes. They know where to look!