My Son just bought an '03 3500 and the horn doesn't work. We have power at the fuse box on fuse 45. There is no power to the plug at the bottom of the clock spring, no power from the clock spring to the horn plug at the top of the airbag to the horn switch. We have replaced the clock spring to no avail.
This truck was an auto at birth but has been converted to a 5 sp. I found while searching this forum that there was a safety recall for the autos in this year and they made the horn come on if the truck was in reverse with the door open. Does anyone know what the recall did to make this happen ? Could the fact that there is no longer an auto plugged into the electrical be the reason for the horn not working ? If so, any ideas on where to look and what to look for ?
Need to get the horn working to pass inspection to get it registered.
Also no power to the cruise control at the bottom of the clock spring either.
Any help would be greatly appreciated.

 

Also, we bought a Chilton's manual for the truck and the only mention of Horn in the index is to R&R. Nowhere on any of the wiring diagrams is there any info on the horn, so after checking the obvious we are driving blind here.

 

Well it looks like the horn relay is controlled by the FCM. The horn switch goes through the clock spring and up to the instrument cluster.

 

Thanks for the reply. FCM is Fuel Control Module ? Where is that located ?

 

Sorry, front control module. It's mounted to the IPM (integrated power module), aka the fuse block under hood.

To remove it, you have to (disconnect batteries, then) partially remove the IPM, then take out some screws and pull straight out. There are 49 pins in the connector.


The FCM talks to everything via the PCI bus, and it controls power to headlights, washer, wipers, fog lamps, park lamps, and horn relay.


It may not be the FCM, since the FCM receives its signal from the instrument cluster, and the horn switch is hard wired to the cluster.

I'm leaning more about your truck's electrical system than I wanted to know...

Basically what I'm saying is that you really should find a scan tool that will communicate with the various control modules - IPM and the Cluster and see if it's getting a signal from the horn switch.

 

Thanks for the reply and the research. I'm guessing that the FCM is the flat square module mounted between the IPM and the fender. It appears to be the only thing mounted to the IPM that's big enough to have a 49 pin connector.
My brother has a code reader/scan tool but it's out on loan. It should be back next week so we'll check that first and see what we come up with.
An update to my earlier add on. The cruise control light does come on when the CC is turned on. It doesn't engage, but that's a minor problem for another time. The main focus is to get the horn working so it'll pass inspection to get it registered. It has a 30 day tag now that gives a pass on the inspection and there's three weeks left on that. Worst case we can get one more 30 day tag then time's up.
I appreciate your help and will keep you updated.

 

Yeah I didn't see a picture, just says to partially remove the IPM and unscrew it. Might be mounted to the bottom of the IPM.

Is your brother's scan tool a $1000+ full function or just an OBD2 tool? You're going to need something high end so you can talk with the cluster.