How to make those silent Freightliner turn signals buzz, squeak or chime!
Right off the bat, let me say the credit for this belongs to Rudy Morris, former webmaster of the Freightliner Chassis Owners Club web site and generally a guru for all things Freightliner. Way to go Rudy!
The modification is fairly simple and as far as I know has no deleterious effect on the Freightliner electronics. As always, any modification you undertake based on anything you read about or see here is undertaken completely at your risk. Every modification on my web site are ones that I have personally done and tested but you might not have the same results! Still with me?
Sometime in 2004 Freightliner deployed a data gathering and presentation system with the heart of it being the MMDC or Multiple Module Data Computer. The MMDC receives input from the ECU (Engine Control Module) , TCU (Transmission Control Unit) and the (ABS/ECU) Anti-lock Brake System Electronic Control Unit and distributes it to the warning lamps, gauges and the Info Center.
This was a great piece of design and engineering except for two things: the original and completely useless display for the Info Center (product of the Medallion Corp.) and absolutely silent turn signals. Freightliner "fixed" the crappy Info Center display by requiring owners with the useless display to spend $75 for an upgrade. This is ex-labor; I don't know what it would cost to have it done.
The silent turn signals are apparently not an issue with anybody except owners/operators of the chassis - it seems very odd that Freightliner has not addressed this with an "official" upgrade. That's okay - we can take care of it ourselves!
This modification ONLY applies to owners with a late model Freightliner chassis. I have no idea if your chassis qualifies for this mod - you'll have to figure that out yourself!
First thing is for you to download and study Rudy's documented modification:
Note that Rudy uses one buzzer and two diodes. This is an elegant solution; one diode goes to each lamp lead and the other diode ends go to the positive input of the buzzer. I didn't want to mess with two diodes so I simply used two buzzers - one for the right turn indicator lamp and one for the left. The positive lead goes to the lamp lead and the negative ends go to dash ground. IMPORTANT: I recommend you use the piezo buzzers pictured below. These have a very low current requirement (15 milliampere or 0.015 amps) and should not cause any problems with the MMDC. You might cause problems if you grab any old buzzer from Rat Shack - some of them have a relatively high current requirement and the MMDC might not drive them successfully.
One more note about the buzzers - the little mini piezo buzzers I used are LOUD! After hooking them up, adjust the volume by placing tape over the grills. Try to adjust them to where you have a nice two-part harmony with the four-way flashers on ;-)
The buzzers I used
It has been a few months since I added the buzzers, so my memory isn't' as fresh, but I believe this is the wiring harness that plugs into the back of the two row idiot display panel. At any rate, this picture when combined with Rudy's directions should make the job fairly simple