My Tom Tom GPS slowly died this year. Replaced it with a Garmin RV870. The old GPS was wired to upfitter 2 and worked great for a decade. I just tried to wire the Garmin to upfitter 2 and it didn’t work. Here’s the rub:

The guy who attached the Tom Tom to the upfitter did it oddly. He tapped into the wire at the switch. I’m assuming he didn’t know about the four wires just above the brake pedal. When I put my volt meter on there set to DC 20V (I don’t have a 12V setting) it reads 4.9. When I hook the Garmin up either to the splice or properly at the green wire in the little cluster, it doesn’t have enough power to power it up (the battery is real low). I get the logo then it reboots.

When I put the meter on the 12v power adapter I cut off the cord, it reads 5.4, which is what it should be.

Any ideas as to why I am not getting the full 12 volts at the upfitter? Secondarily, how would I translate the 4.9 and 5.4 to an actual 12 volt reading? Has to be some sort of math. Kind of surprised the multimeter doesn’t have a 12 volt setting for DC. It does have a BAT setting with a 5V and 11.5V setting, but both of those don’t read right either.

Thanks for any insight. I have an appointment for Monday afternoon for a speed shop to look at it but this should be elementary stuff that I am somehow missing.

 

I'm gonna say 4.9VDC is 4.9VDVC, and same for 5.4. Or maybe your multimeter likes the straight six and the modular motors

I have no idea why you're not getting full voltage but I don't think you need to convert anything. You're not tapping into a switch illumination wire or something?

For giggles put your meter on the battery - what do you get? Then when running you should see more...likely 13.8 to 14.4ish....barring any BMS-esque trickery, but these trucks shouldn't have BMS (my '11 doesn't)

 

You are correct, WWR. Thank you for clarifying. I put the meter on my battery and it is showing 12.9. When I put it on the adapter I cut off direct in the 12v outlet it shows 5.4. Any idea what might be going on?

 

has me wondering if they are properly installed, if the guy tapped in the wrong location obviously didnt know about the actual connections.
4.9v sound like its for a usb hub, upfitters don't have that.

 

Figured it out. Took about three hours today of messing with the existing wiring before I said screw it and ripped the dash apart to see what was doing. The old GPS wire was visible up top. I cut its head off and metered the leads and they were 5.2v, right where they should be. Made no sense to me, but I decided to use those leads to power the new GPS. Got it all up and running but when I buttoned it all back up it didn't work. That's when I pull the dash apart.

Just below the radio was the cause of the angst... They wired in a power receptacle and put the 12v adapter from the previous GPS into it and taped it up. Bottom line is the GPS requires 5.2 volts to run properly. Had I simply wired in my leads to 12v I may have fried the unit. I removed all that and repaired where they tapped into the switch wire. I pulled the new cable through the dash (love the little access panel up top) then put their adapter onto the upfitter blunt where it belonged, attached it to ground properly (where two of the other upfitters are attached) and tested. Reassembled it all and we're good to go. Some good learning lessons the past couple of days. What I don't fully understand is why the upfitter blunt was reading 4.8 downstream from where they tapped it. Somehow the current was getting diminished by the device on the tap, but it wasn't a direct connection. Odd.

Thanks for looking in and offering your advice. It's done and I have a new skill. Peace.

 

The one thing I hate more than anything is Cletus+wiring. I can deal with hack exhaust, hack bodywork, hack engine work but hack wiring makes me want to put on a giant diaper and hockey mask and run around with a giant axe killing everyone in sight.....

 

I grew up with the shop that did the install’s owner. He sold it a couple of years ago. I sent him pics of the wiring today. He was mortified over what his team did. He was out sick with throat cancer back then when I took the truck in to get wired. He said he never would have approved that job.