Manual GPR Switch
Thread Starter
|
Freshman User
Joined: Aug 2005
Posts: 27
Likes: 0
Manual GPR Switch
I just completed the manual grp switch as explained by kwikordead. I notice that I get 12v on the switch after the truck is started. I have it wired exactly as described so I just want to confirm this is normal. Just to explain....small post jumped to constant hot big post. Other small post ran to my momentary with the other side grounded. I'm just confused as to why I have 12 volts on switch when it's in it resting place (not pressed). Thanks.
Cargo Master
Joined: Oct 2010
Posts: 2,089
Likes: 16
It will read voltage until you ground it. The same way your GPR read voltage on the small ground wire after you fried your pcm. However, if u wired like u said, it seems as though the momentary switch would always have power regardless of ignition switch postion.
Mine is wired so that i only control the ground side of the circuit. I still use the keyed 12 v from the truck to engage and I just ground it when I want it with the momentary.
Mine is wired so that i only control the ground side of the circuit. I still use the keyed 12 v from the truck to engage and I just ground it when I want it with the momentary.
Cargo Master
Joined: Jun 2010
Posts: 2,771
Likes: 3
From: Louisiana
I don't mean to hijack but when you say fried his PCM, what do you mean? Why does he need this momentary switch? I'm working on a truck that constantly has a P0380 code. From testing the best I can come up with is there is a short of some sort coming from the control wire. Thanks!
Cargo Master
Joined: Oct 2010
Posts: 2,089
Likes: 16
i will send u pm bulla. Trucks not here now or I would go look but is there anyway that the wires for the AIH solenoid can be mixed up and put onto the GPR?
Michael, what colors are the two control wire on the GPR?
Michael, what colors are the two control wire on the GPR?
Thread Starter
|
Freshman User
Joined: Aug 2005
Posts: 27
Likes: 0
I used the relay that is closest to the firewall. I thought the bigger of the 2 relays (the frontmost) was for the IAH??? As far as my wire colors....I know the one on the furthest (closest to firewall) small post was pink and I'm not sure about the other one. I 'll check tomorrow morning. I'm not using either of those wires now. I have them insulated and taped off. I ll try t upload a pic tomorrow. Just to clarify on the wiring...the frontmost small post jumped to the big constant hot. The furthest small post (closest to firewall) comes into the cab to one side of my momentary. The other side of the momentary is grounded.
Thread Starter
|
Freshman User
Joined: Aug 2005
Posts: 27
Likes: 0
It will read voltage until you ground it. The same way your GPR read voltage on the small ground wire after you fried your pcm. However, if u wired like u said, it seems as though the momentary switch would always have power regardless of ignition switch postion.
Mine is wired so that i only control the ground side of the circuit. I still use the keyed 12 v from the truck to engage and I just ground it when I want it with the momentary.
Mine is wired so that i only control the ground side of the circuit. I still use the keyed 12 v from the truck to engage and I just ground it when I want it with the momentary.
Trending Topics
Cargo Master
Joined: Oct 2010
Posts: 2,089
Likes: 16
You are correct about location of GPR. So the new pcm fixed the original control circuit issue but you are just wanting it to be manual? If so, then all is good. Your momentary switch will have power showing as until it is grounded. Same it was in your original post when you had voltage on both small terminals of the GPR since the pcm was not supplying ground to the system.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Thread Starter
|
Freshman User
Joined: Aug 2005
Posts: 27
Likes: 0
I see. I was under the impression that the gpr needed one side to be 12 volts and the other side to ground meaning the circuit would not be complete until it had its ground. I think I need to read more about relays instead of assuming. Is there anyway to make a switch that wouldn't have 12 volts on it at all times? I know that there are always wires that will be hot regardless of key position but I am extremely weird about electricity. I would turn the main off to my house every time I leave if it was just me. Thanks for the information.
Hotshot
Joined: Jan 2002
Posts: 17,988
Likes: 207
From: La La Land
What you are seeing is completely normal.
The voltage you are reading is the voltage on the other terminal, and you are reading it on the other terminal because it is being passed THROUGH the relay's coil wire. It is not grounded, so there is no CURRENT passing through the coil, thus no magnetism, thus no relay ACTIVATION.
When you ground the wire you are seeing voltage on, current passes from the always-hot terminal, through the coil wire (causing magnetism) and finally to ground, completing the circuit from hot to ground. When that wire is grounded, what's the voltage on that terminal? Zero! Why? It's on GROUND, that's why.
When you again lift that wire off ground, there's no coil current flow to ground, and no magnetism created. But you are once-again going to read the voltage that's over on the other (hot) terminal through that coil's wire.
If you have voltage on one end of a wire, you will have voltage on the other end of that same wire, even if no current is flowing.
Clear as mud??!!??
Pop
The voltage you are reading is the voltage on the other terminal, and you are reading it on the other terminal because it is being passed THROUGH the relay's coil wire. It is not grounded, so there is no CURRENT passing through the coil, thus no magnetism, thus no relay ACTIVATION.
When you ground the wire you are seeing voltage on, current passes from the always-hot terminal, through the coil wire (causing magnetism) and finally to ground, completing the circuit from hot to ground. When that wire is grounded, what's the voltage on that terminal? Zero! Why? It's on GROUND, that's why.
When you again lift that wire off ground, there's no coil current flow to ground, and no magnetism created. But you are once-again going to read the voltage that's over on the other (hot) terminal through that coil's wire.
If you have voltage on one end of a wire, you will have voltage on the other end of that same wire, even if no current is flowing.
Clear as mud??!!??
Pop
Thread Starter
|
Freshman User
Joined: Aug 2005
Posts: 27
Likes: 0
What you are seeing is completely normal.
The voltage you are reading is the voltage on the other terminal, and you are reading it on the other terminal because it is being passed THROUGH the relay's coil wire. It is not grounded, so there is no CURRENT passing through the coil, thus no magnetism, thus no relay ACTIVATION.
When you ground the wire you are seeing voltage on, current passes from the always-hot terminal, through the coil wire (causing magnetism) and finally to ground, completing the circuit from hot to ground. When that wire is grounded, what's the voltage on that terminal? Zero! Why? It's on GROUND, that's why.
When you again lift that wire off ground, there's no coil current flow to ground, and no magnetism created. But you are once-again going to read the voltage that's over on the other (hot) terminal through that coil's wire.
If you have voltage on one end of a wire, you will have voltage on the other end of that same wire, even of no current is flowing.
'
Clear as mud??!!??
Pop
The voltage you are reading is the voltage on the other terminal, and you are reading it on the other terminal because it is being passed THROUGH the relay's coil wire. It is not grounded, so there is no CURRENT passing through the coil, thus no magnetism, thus no relay ACTIVATION.
When you ground the wire you are seeing voltage on, current passes from the always-hot terminal, through the coil wire (causing magnetism) and finally to ground, completing the circuit from hot to ground. When that wire is grounded, what's the voltage on that terminal? Zero! Why? It's on GROUND, that's why.
When you again lift that wire off ground, there's no coil current flow to ground, and no magnetism created. But you are once-again going to read the voltage that's over on the other (hot) terminal through that coil's wire.
If you have voltage on one end of a wire, you will have voltage on the other end of that same wire, even of no current is flowing.
'
Clear as mud??!!??
Pop
Cargo Master
Joined: Oct 2010
Posts: 2,089
Likes: 16
If u use the original small pinky red wire (instead of the jumping off the large 12v post on gpr), it will be keyed 12 v if that is what you are asking. It comes from the pcm power relay i think and does not have any interaction with the pcm itself.
If u do that, the 12 v to the small wire will be there anytime u activate the key and the switch you installed will ground it when u want it to work. By adding the switch, you are just taking the place of the pcm grounding the relay on the ground side.
If u do that, the 12 v to the small wire will be there anytime u activate the key and the switch you installed will ground it when u want it to work. By adding the switch, you are just taking the place of the pcm grounding the relay on the ground side.
Cargo Master
Joined: Jun 2010
Posts: 2,771
Likes: 3
From: Louisiana
Well, I just read through most of your other thread and that is just what I'm fighting on an '02. Only difference when I was only getting 6.5 volts to the gpr key on power wire it was because a fuse had burnt. On this truck it wouldn't let it start at all. Changed fuse and the 12 volts are back, but I still can't get any ground from the PCM. Called Jody today and he verified with me that just the gpr function can go in the PCM but the rest of the truck still function as is supposed to! Glad I found this read.
Did you ever try letting the PCM control the gpr since you replaced the PCM? Why not? Where and how much was that PCM you purchased?
Did you ever try letting the PCM control the gpr since you replaced the PCM? Why not? Where and how much was that PCM you purchased?
Thread Starter
|
Freshman User
Joined: Aug 2005
Posts: 27
Likes: 0
Well, I just read through most of your other thread and that is just what I'm fighting on an '02. Only difference when I was only getting 6.5 volts to the gpr key on power wire it was because a fuse had burnt. On this truck it wouldn't let it start at all. Changed fuse and the 12 volts are back, but I still can't get any ground from the PCM. Called Jody today and he verified with me that just the gpr function can go in the PCM but the rest of the truck still function as is supposed to! Glad I found this read.
Did you ever try letting the PCM control the gpr since you replaced the PCM? Why not? Where and how much was that PCM you purchased?
Did you ever try letting the PCM control the gpr since you replaced the PCM? Why not? Where and how much was that PCM you purchased?