2007 Pete 378 turn signal issues

Truck is a 2007. No right turn signal. I don't have a wiring diagram. I cannot find a flasher brick anywhere.the flasher actually seems to be in the instrument cluster. There are 9 relays behind and below the cluster but cant figure out what they are for . When the cluster is plugged in the left turns and left hazards work fine. When the cluster is unplugged nothing works. I could really use some advice!

 

Thanks for the reply. Sadly all bulbs are new. To rule out switch problems I disconnected the stalk and using a test lamp to ground, I can actuate left signals via the pin, however the right does not respond. Anybody know where i can find peterbilt 378 diagrams? It is significantly different than the 379 diagrams i have.

 

Well I was wrong! The left signal and hazard do still work when the cluster is unplugged. But since the noise maker is in the cluster and that obviously goes away I missed the actual bulb continuing to flash. This thing must have a electronic flasher because it makes absolutely no noise. I cant find it. I pulled each one of those nine relays while the left turn was on and flashing. It never went out so that tells me they aren't for turn signals.

 

Thanks for the reply! That's where I found the 379 diagrams. I'll look again, but I didn't find any 378 diagrams there.

 

Thanks for the replies! Learn something new each day I guess. I never understood that the major diff between 378 - 379 was aluminum/fiberglass! Interesting since I have both trucks!
Anyway, we can rule out any lighting issues with the chassis wiring harness since it is disconnected at
the cab. The way this thing all started? Driver had to turn tight. Pigtail got snagged, jerked the receptacle from the trailer. When the truck got back to me right side of truck was out. I went thru the wiring for the chassis and fixed all those issues. Now I am down to the right turn signal issues.
#1) No right turn signal. And no indication of the right turn indicator on the dash. If this were a bulb / ground issue I would expect the indicator to be on in the dash.
#2) With the hazards on, the right side does not flash and turning on the right signal kills the hazards... This does not happen when turning on the left signal. Ie the hazards continue to flash.
I'm suspecting the MFTS module but I'm not sure how to rule it out?

 

Sorry it's taken so long to get back to this. As it turned out, this problem had two separate issues. First the fuse box is trash in this truck. While the right turn fuse was good, the fuse's terminal didn't always make contact. Secondly, there was an open in the dash power wiring for the right turns. I really got burned by the lack of good info on that MFTS module. In the end the only way to rule that MFTS module out was to replace it with a known good one ... Yup 650$ just to prove there wasn't anything wrong with the original!

So here is what I learned about the turn switch, flasher, and MTFS module:

Turn switch:
First the turn switch isn't represented on the 98 page Model 379 schematic (P94-6023.pdf)
And the connector shown on the diagram for the turn stalk is incorrect. I'm mean jeez guys, a ground pin AND a switch common! The engineer who drew that almost certainly was looking to confuse anyone who tried to decipher that!!! The pin listed as pin 12 (switch common) is the ground and there is no Ground wire in pin 1. So how the hell do you get left/right with only 2 pins? Well, here's the answer.
The left/right turn input on pin 2 is a 3 state analog input to the mtfs module. The stalk has a single pole double throw switch for the turns as would be expected. However one throw is connected to a 300ohm resistor and the other throw is connected to a 1k ohm resistor with the common leg of the switch connected to the left/right turn input of the mtfs module ie. pin 2. The other leg of the resistors are connected together to pin 12 ie. ground. Pin 11 of the mtfs module is a high impedence input pulled up to 12v so when the 300ohm resistor connected to ground, is selected via the turn stalk, the input voltage on mtfs pin 11 is about 6v. When the 1k ohm resistor connected to ground, is selected via the turn stalk, the input voltage on mtfs pin 11 is about 9v.

MFTS: PIN 11 ( left / right turn input )
12v == turn signals off
9v == left turn signals on
6v == right turn signals on

All that to save one stupid wire!
Thanks Peterbilt

FLASHER:
I never did find a flasher unit in this truck. I know beyond the shadow of a doubt that the MTFS unit does the flash for the turn signals. I'm just not certain yet how the hazards get flashed?

Hopefully I have helped someone else get to the root cause of their turn signal issues!