Headlights flick on off then back on when hooked to our towed jeep

[Lynn Hales]

After our Cadillac SRX was totaled recently I had our  Demo air force one system installed in our '21 Jeep Grand Cherokee.  The brake piston is working fine and so is the brake and turn signal lights. However, when I turn on the coach headlights on about every 15 seconds the coach lights and jeep lights briefly turn off and then immediately turn back on. This on/off continues until I turn off the coach headlights.  I'm clueless where to even begin to try to track this down. Anybody got any ideas or recommendations? Lynn

 

'06 Monaco Diplomat PDQ

Towed: was a 2016 Cadillac SRX, now its a '21 Jeep Grand Cherokee

 

[Ivan K]

Are the jeep lights connected to your headlight circuit somehow? Suspect the rear lights would do the same? Your headlights would typically be on an auto-resetable breaker and that's what is likely tripping under an additional load.

Edited March 14, 2023 by Ivan K

[Lynn Hales]

1 hour ago, Ivan K said:

Are the jeep lights connected to your headlight circuit somehow? Suspect the rear lights would do the same? Your headlights would typically be on an auto-resetable breaker and that's what is likely tripping under an additional load.

Thanks Ivan, When the Air Force brake system was installed so was a wiring harness on the jeep. I assume it is wired into the 7 wire umbilical that connects the coach to the jeep.  Any idea where the "resettable breaker" might be located in case I destroy it as I troubleshoot?  

I never drive at night so I hope that I'll be driving as it is currently wired as long as the coach lights are off.

[Gary 05 AMB DST]

Do you have to disconnect a fuse to tow the Jeep?

Gary 05 AMB DST

[Ivan K]

With so many years between ours and your coach, hard for me to tell but the breakers for my lights (20A for low and separate 20A for each high) are in front run bay.

[Harvey Babb]

The headlight switch itself will sometimes have the breaker as an integral part of it.

I first ran across this over 40 years ago when the çlearance lights on my car shorted out from a pinched wire.

[Lynn Hales]

1 hour ago, Gary 05 AMB DST said:

Do you have to disconnect a fuse to tow the Jeep?

Gary 05 AMB DST

Gary, no, no fuse to disconnect.  Just a process of getting the transfer case into neutral. Lynn

1 hour ago, Ivan K said:

With so many years between ours and your coach, hard for me to tell but the breakers for my lights (20A for low and separate 20A for each high) are in front run bay.

Ivan, I'll poke around the front run bay and see if I can find anything.

1 hour ago, Harvey Babb said:

The headlight switch itself will sometimes have the breaker as an integral part of it.

I first ran across this over 40 years ago when the çlearance lights on my car shorted out from a pinched wire.

Harvey, I replaced the headlight switch itself last year and it was just the normal simple switch, no integrated breaker.

 

[bobdinsmore]

I think you're overloading the headlight switch. Years ago on my Diplomat I had this on-off -on-off- problem when I increased the headlight bulb wattage with brighter bulbs. There is a thermal in the headlight switch itself that is heating, cooling, etc. I think you'll find the stem to the headlight switch is very hot to the touch when you're having the problem. I added a relay to the headlight switch to take the heavy current load off the switch. This fixed the problem.

[Lynn Hales]

3 hours ago, bobdinsmore said:

I think you're overloading the headlight switch. Years ago on my Diplomat I had this on-off -on-off- problem when I increased the headlight bulb wattage with brighter bulbs. There is a thermal in the headlight switch itself that is heating, cooling, etc. I think you'll find the stem to the headlight switch is very hot to the touch when you're having the problem. I added a relay to the headlight switch to take the heavy current load off the switch. This fixed the problem.

Thanks Bob, I'll bet you're right.  Do you have a relay type, or number. I'll need to get it sized correctly on the output side for the full current draw of the coach lights and the towed lights I guess.  Lynn

[TommyL]

Lynn ,I have the same problem.headlight switch gets cat cookin hot! These were made for 2 headlights 2 taillights, At least I hope that’s the problem, would like to know more about Bobs relay fix.

[bobdinsmore]

You need a four-pin R87 relay, available at any auto parts store. Here's a diagram. Cut the headlight-switch wire that goes to the headlight and attach the ends of the cut wire to Pins 86 and 87. This uses a low current signal (triggers the relay) from the headlight switch to drive a high current to the headlight, ie, you're offloading the high current from the headlight switch.

Pin 30 = Battery 12v (Fuse this line)

Pin 85 = Frame ground

Pin 86 = From headlight switch

Pin 87 = To headlight bulb

[Lynn Hales]

20 minutes ago, bobdinsmore said:

You need a four-pin R87 relay, available at any auto parts store. Here's a diagram. Cut the headlight-switch wire that goes to the headlight and attach the ends of the cut wire to Pins 86 and 87. This uses a low current signal (triggers the relay) from the headlight switch to drive a high current to the headlight, ie, you're offloading the high current from the headlight switch.

Pin 30 = Battery 12v (Fuse this line)

Pin 85 = Frame ground

Pin 86 = From headlight switch

Pin 87 = To headlight bulb

Bob, thank you!  Clear and understandable. Now if I can just remember how to get the light switch stem to come off so I can get the body of the switch to a spot where I can work on it. Lynn 

11 hours ago, TommyL said:

Lynn ,I have the same problem.headlight switch gets cat cookin hot! These were made for 2 headlights 2 taillights, At least I hope that’s the problem, would like to know more about Bobs relay fix.

Tommy, I'll post after I make the modifications. It seems real logical to me. although I'm not 1000% sure the fellow that wired our towed car totally knew what he was doing. It's one thing to say you know how to do something and something else all together to actually know.  Lynn

[bobdinsmore]

To release the headlight switch stem, reach up under the dash and there is a pushbutton on top of the switch. Push the button and pull out the stem.

To trace the wires thru the plug to the back lights, get a 12v wire tracer at NAPA, the one that has an alligator clip hook to ground and a sharp-pointed light in the handle. Then activate each of the functions one by one while probing the terminals to find which one lights the handle.

Edited March 20, 2023 by bobdinsmore

[Lynn Hales]

On 3/20/2023 at 7:04 AM, bobdinsmore said:

You need a four-pin R87 relay, available at any auto parts store. Here's a diagram. Cut the headlight-switch wire that goes to the headlight and attach the ends of the cut wire to Pins 86 and 87. This uses a low current signal (triggers the relay) from the headlight switch to drive a high current to the headlight, ie, you're offloading the high current from the headlight switch.

Pin 30 = Battery 12v (Fuse this line)

Pin 85 = Frame ground

Pin 86 = From headlight switch

Pin 87 = To headlight bulb

Bob, I've begun to install a relay.  Turns out the wires feeding the headlight switch are labeled. They are: H) dome, C) dimmer, B) dome light, A) headlight pwr, F) marker pwr, E) marker to VIP, J) headlight to VIP.  

When the coach 12V master switch at the batteries in on 12V appears at A and F, even when the headlight switch is off.  When the light switch is off there is no 12V on J.  When I turn on the lights 12V appears at J so I'm assuming that I should cut the wire from J and attach the end coming from the switch to terminal 86 on the relay and then attach the the cut end that in marked headlight to VIP to terminal 87 of the relay.

I thought I could connect terminal 85 on the relay to H, the Dome gnd.

After this I need to find a new source of 12V that can provide enough amperage to power the coach headlights and the new load of the the towed vehicle and connect it to terminal 30. And I need to fuse this line. I was thinking of a 20A fuse.  I'm really not sure where to pick up an appropriate 12V line for terminal 30.

Does this all sound correct to you?  Lynn

[Ivan K]

Just my opinion but since it appears that you have a smart wheel and VIP controller, I would leave the switch alone and connect the relay coil past the controller, pin P12-2. That way both the switch and controller are protected from overcurrent. Also this would preserve the CIC function the way it is. I don't see whether you say that your high beams are flashing also but suspect they already have relays on them and work alright? I don't really understand how or why the jeep headlights come ON, if I read it right...

Edited March 21, 2023 by Ivan K

[Lynn Hales]

14 minutes ago, Ivan K said:

Just my opinion but since it appears that you have a smart wheel and VIP controller, I would leave the switch alone and connect the relay coil past the controller, pin P12-2. That way both the switch and controller are protected from overcurrent. Also this would preserve the CIC function the way it is. I don't see whether you say that your high beams are flashing also but suspect they already have relays on them and work alright?

Ivan, thanks for your thoughts and drawing.  Any idea where the VIP controller is? If I understand your comment correctly you are suggesting that the relay be inserted where the "low beam" writing is located.  Correct? 

[Ivan K]

Yes, that would be my preference as it would only feed the low beams. My controller in is the front run bay but there are many model years between us.

[bobdinsmore]

I do not have a smart wheel on my 200 Diplomat so you should follow Ivan's suggestions. He is extremely knowledgable on things RV!

[Lynn Hales]

On 3/21/2023 at 2:26 PM, Ivan K said:

Yes, that would be my preference as it would only feed the low beams. My controller in is the front run bay but there are many model years between us.

After much digging under my dash I finally found the VIP module. SM211 Rev B.  I've also scoured my front electrical bay. Without tracing wires from the VIP to the main board in the front bay but looking at all the connectors and relays and labeled wires I'm now thinking that there is already a relay after the VIP.  I'm going to try to do some tracing to confirm my suspicions tomorrow. 

The J2 connector show #5 to be head lamp src and #6 as head lamp pwr. Do you know what src stands for?

 

 

[Ivan K]

Ok, your controller is much newer than mine and apparently quite differently wired but SRC typically stands for 'source', like a source of power that is switched on/off to the output. If this is the low beam relay, there still might/should be a breaker in its switched circuit 30->87.

Follow up

I just noticed your circled pin positions in 2nd pic,  I don't know which pin is for what, lower center might be your scr but they don't necessarily need to correspond to J2 pinout. However, there is a PCB trace to a breaker that is not in the picture and might possibly be what is cycling it on/off.

Regardless, I still don't understand why the jeeps lights would be wired to headlights. Mine are on marker lights circuit and that makes more sense me, so they light up in Park position. No headlights needed on the toad when hooked up.

Edited March 23, 2023 by Ivan K

[Lynn Hales]

9 hours ago, Ivan K said:

Ok, your controller is much newer than mine and apparently quite differently wired but SRC typically stands for 'source', like a source of power that is switched on/off to the output. If this is the low beam relay, there still might/should be a breaker in its switched circuit 30->87.

Follow up

I just noticed your circled pin positions in 2nd pic,  I don't know which pin is for what, lower center might be your scr but they don't necessarily need to correspond to J2 pinout. However, there is a PCB trace to a breaker that is not in the picture and might possibly be what is cycling it on/off.

Regardless, I still don't understand why the jeeps lights would be wired to headlights. Mine are on marker lights circuit and that makes more sense me, so they light up in Park position. No headlights needed on the toad when hooked up.

I should have clarified my original problem statement sooner. With the coach engine on, and the jeep all connected up, the jeep turn signals and brake lights work correctly. When I then turn on the coach headlights on the brake and turn signals still work but on about a 10-15 second frequency, standing behind the jeep the jeep running lights go off and then turn back on after a second and then this continues to occur until the coach headlights are turned back off.  I guess I've been looking for the problem in the wrong place.

[bobdinsmore]

I'm going to make an educated guess: I believe the Jeep taillights were spliced into the coach's headlight circuit instead of into the coach's taillight circuit. All these extra bulbs are what is overloading the coach's headlight circuit and causing the flickering. Move that one line in the coach from headlight to tail/running.

Edited March 23, 2023 by bobdinsmore

[Tom Cherry]

42 minutes ago, bobdinsmore said:

I'm going to make an educated guess: I believe the Jeep taillights were spliced into the coach's headlight circuit instead of into the coach's taillight circuit. All these extra bulbs are what is overloading the coach's headlight circuit and causing the flickering. Move that one line in the coach from headlight to tail/running.

My thoughts also.  I would verify the wiring.  I would highly recommend that the Roadmaster diodes be used to protect the Jeep’s electronics.  This is a simple process and the Roadmaster diodes have great and comprehensive (simple) instructions.

[Lynn Hales]

Thanks Bob, Ivan and Tom, I'm now tracing all the wires through the coach 7 way back to the tail lights. I think there may already be diodes hidden bay there but I'm going to have to work from the ground up and top down to find out. I also discovered that I don't have a charge wire for the jeep battery.  On the coach side I've got a constant 12V on one of the spades. I guess that is the one to run over to the jeep for the charge wire.

[Larry Laursen]

The connections in the trailer connector on a 06 Dip go through a separate supply. The fuses are in the plastic box in the passenger side rear compartment.  There are relays in the rear distribution so not adding to the load.  The attachment is the wiring schematic.

2006 End_Dip Chassis Wiring.pdf