Buzzing Modulite converter

[tgiaTDI]

Recently I purchased and installed a Hidden Hitch. I was missing the towing harness which I purchased from RedTrailers.com and followed the instructions I found here to proceed with the installation last night.

Like most people, I used the 12v power outlet on the right side of the trunk to connect the power line and positioned the fuse holder so that I can access it through the taillight opening on the left. Tested the whole thing with the End cover with led lights tester and it worked perfectly. Left/Right turn signals, taillights, brakes, no problem, no sound, no smoke. So I put the trunk liner back in place and tested again. To my surprise, this time the module is buzzing when the lights were turned on or in sync with the turn signals. Pretty loud too, I could hear it from the driver's seat.

The only difference from the time I first tested it and the time when it started buzzing is that I re-plugged the power outlet before putting the trunk liner back. Since it was already dark out, I had no more time for debugging. So, before I take it all apart again tonight and start troubleshooting, does anyone have a clue as to where the problem could come from?

TIA

 

[tgiaTDI]

I guess I'm the first to experience this issue.

I've no experience with electrical gremlins so any input or theory on what I should check for could help. The module functions properly, all lights respond like the first time but the buzzing is really loud and it sounds like a surcharge, short circuit or something, although the fuse doesn't burn... and it buzzes in synchronization with the turn signals (at the 'on' position) or constantly with the lights turned on...

 

[Lightflyer1]

I am interested in this as well as I will install mine shortly. You might have to wait a day or so for an answer though.

 

[tgiaTDI]

Just a little update since noone else had that problem yet.

After numerous tests I came to the conclusion that the module itself might be at fault.

I ran a separate 12ga. wire straight to the battery, tested different ground locations, tried another 15amp fuse and even a 10amp fuse, tapped signal wires at different places, tested them independently, tried engine on or off, tested voltage, etc. The buzz continues the moment there's tension with no evident car/installation problem.

I have contacted the vendor where I purchased the module and they'll send me a new one today. They have been extremely helpfull in trying to diagnose the problem and will even go as fas as running their own tests on the mk5 jetta platform.

I'll post another update once I (hopefully) succeed in having the new module operate problem-free.

 

[Lightflyer1]

Thanks for the update!

 

[skthom]

I also have a modulite convertor installed from the thread you referenced. I didn't have any issue with the install and it still all working just fine. I use my Jetta to pull a 3 rail dirt bike trailer...

Here's my thread on the subject...
http://forums.tdiclub.com/showthread.php?t=182410

 

[tgiaTDI]

Yeah, I'm lucky like that. Works on every other car xept on mine

Well, after my last post I uninstalled the module in order to send it back once the new one comes in. But, that same night the vendor's senior tech (with over 20 years experience in the field) called me with a few more questions. He concluded that I should try one last thing before they send me a new module. He said that I should ground the RED wire in order to completely close the circuit.

Haven't had a chance to try that yet since the next morning my car went straight to the dealer for a repeating "Flashing Glow Plug Light -> Limp Mode unresettable by engine on/off procedure" problem that I had every morning after a humid night. Supposed to pick it up tonight. Apparently they had to change the Throttle Pedal sensor (which didn't help) then the Glow Plug Harness (which fixed the problem). I'm picking it up tonight.

Ironically, having read about other people with similar problems, I told them it might be the harness but what can you do... Gotta let them run their scripts.

 

[tgiaTDI]

The mistery continues...

Ok, so it seems that it's not the module. I did more tests and it only gets more puzzling, but I'm getting closer. After grounding the red (stop) wire, the buzzing is still there.

Tested each signal wire independantly once again, same results. Then I had the idea of disconnecting the LEFT (driver's side) tail light/flasher plug and test again. Surprise, this time, no buzzing. Because the circuit is not closed, the left flasher signal doesn't get through if the plug is not connected and the car detects a burned out bulb (idiot light comes on).

So, it seems that the problem only exists if the plug is connected to the tail light. Didn't try the right side nor did I mesure voltage this time (getting dark, didn't have all the tools, etc.). Bulbs are all good and I have no dimm lights or flashers anywhere on the car. I also exclude the bad ground or low voltage theory as far as the module goes. The problem comes from the signal wires and ONLY when the tail light plug is connected.

Any ideas? C'mon ppl, there must be an electrical guru around here...

 

[SuperJ]

The Jettas lights are not always lit by 12volts if I recall. The voltage varies depending on the purpose of the lighting action.

Perhaps the modulite utilizes 12v relays which aren't strong enough to pull completely under a 3-6volt source? Instead the relay chatters causing a buzz.
I've seen the problem with low voltage on refrigeration equipment contactors. The compressor goes to start and causes enough of a brownout from the inrush current that the contactor temporarily cuts in and out under too low of voltage.

Just a thought.

 

[Strider]

The issue here is that the Jetta dims its lights using PWM (Pulse Width Modulation) as I recall. Basically, the control module flashes the lights very quickly (Say a few thousand times a second) and how long that flash determines how bright the light will be.

The buzzing you're hearing is probably from the PWM frequency. If the module is relay based, that would definately cause it. Ideally you want a solid state (read transistor based) unit that is capable of handling a PWM source.

 

[tgiaTDI]

Thank you SuperJ and Strider.

Strider, I think you may have hit the nail on the head (is that an expression?). The module is relay based and the vendor last mentioned that I might need a different style converter... without relays.

 

[tgiaTDI]

For those who might want to know.

Solid state unit installed, functional and chatter-free

 

[Lightflyer1]

What module are you using now? Did they send you a different one or did you change to another? What is the model number of the one you are using? I am about to do this myself and currently have one of the modulite converters.

 

[tgiaTDI]

The vendor was very cooperative. They sent me a new unit (31825).

Both units are made by Hidden Hitch and look identical but one is relay based (with smart circuit procection, uses 15amp fuse) while the other is a solid state unit (10amp fuse).

There's also no difference in the way I installed the new unit compared to the problematic one. Good luck

Relay based unit (wrong one): 31824

Solid state unit (correct unit): 31825

 

[Lightflyer1]

Thank you very much! I will check mine tonight when I get home.