ok, so my wife bought me a train horn for my truck as an early xmas present. i was wiring it up yesterday and the kit comes with a relay that has to be wired to a hot power source with the ignition on. any suggestion as to what might be the best wire to tap into. i mounted the relay on the passenger side inside fender next to the battery, but the fuse box is located on the driver side next to the other battery. thanks.

 

A pretty easy way is to run piggy-back from a fuse in the fuse panel, and through the firewall to your relay. Pick a fuse labeled for power windows or something that you know only works with ignition "on". This way you dont cut or splice into anything and can go back stock anytime. Radio shack will have the little "piggy backs" to attach to a fuse for cheap.

 

There are some "customer access" points in the fuse panel that supposedly have some wires tucked up under the dash you can tie into for this. I'm getting ready to add heated seats to my truck so I've been poking around. I found about 4 wires under the dash and another 4 wires under the hood that are folded and taped to a wiring harness with heat shrink on the ends.

I've seen other posts here where someone would post the wire colors for these spare wires but they seemed to vary by year model. Since I don't see colors that well I plan on just using a volt meter to see what wires hot when and which fuse kills it.

I'll snap a few pics this weekend when I play with it again if your interested.

 

I've not heard that before. Very good information. I'll be watching cause it wil come in useful for heated mirrors.

 

If you look in your owners manual under the fuse section it labels 2 or 3 different fuse locations, and I believe 1 relay as customer access. You just have to find what wire goes where.

https://www.ford-trucks.com/forums/2...use-block.html

Semper Fi Orezona

 

[QUOTE=F350-6]There are some "customer access" points in the fuse panel. I found about 4 wires under the dash and another 4 wires under the hood that are folded and taped to a wiring harness with heat shrink on the ends.
QUOTE]

I think you will find these 4 wires only go from dash and go to the engine side of the firewall under the brake booster.. There is no power at all to these wires.. Anyway not in my 99, ignition on or off.. But the piggy back is a good deal. I learned something. That new to me.

 

I wondered about that as I was trying to push a wire through my firewall for the new fog lights. The link I posted mentioned wires taped up near the OBDII plug. I haven't looked over on that side yet but plan to this weekend.

Since the owners manual does list the customer access point I'll at least find out which wires go to those fuses even if I have to pull the fuse block and test every one of them. I'll let you know what I find.

 

This is what I also found in my 02. In the engine bay, they are taped to the wiring harness that goes across the back of the engine bay, under the windshield. Located above the brake hydroboost. In the cab, I found the other end of the wires on the kickpanel above the PCM.

For "Power when ON", I have used the Aux Power Control Module plug located behind the fuse access panel, clipped on the lower right side metal frame of the dash. I have also used the Gray w/Yellow trace 12 guage wire that comes off of the Ignition switch. This wire is used for heated seats and is ON only in run position.

 

That sounds exactly like the wire I'm hunting for my heated seat install.

Thanks.