Mystery wire connection. Any ideas?

[BuffaloGuy]

Since I got my truck back from the mechanic that put the new motor in I have noticed a single wire connection way back behind the fuel filter housing. It was unplugged but was clean inside so it was obvious that it had been plugged in for the prvious 200,000 miles. Look as I could, I couldn't find the other end that it was mated to....unitl today.

The mate came from a loom just as this wire did but was actually resting on the bell housing. Since they both disappear into looms I have no idea where they comes from, where they goe or what it does. Anybody know?

It's a single wire with one of those plastic connector jobbies. It's right at the firewall about the center of the motor. About 4 inches stick out of seperate looms for both ends.

I'd sure like to know what this is for. Maybe it will help my cold start problems!

Thanks for all your guys help. Your a great bunch of guys!
Ken

[ChevyDooley]

I have a whole connector full of connections that I dont know what it does. Its always just sat there on the firewall unconnected. I know how you feel!

[pannhead]

i know its common,especially on the interior depending on accessories etc.....if its a single female spade connector it could a glow-plug wire which come off easily and the glow plugs are hard to see on the drivers side.......just a best guess shot in the dark....good luck ;)

[BuffaloGuy]

Nope. Not a glow plug wire. They are all A-OK. This one is so short that it couldn't reach anywhere. Only about 4 inches sticking out of the loom. Same on the other end it mated to. Guess I'll take a trip to the dealer and see if they can figure it out.

[HowieE]

What color and size is the wire? GM uses standard color for each circuit. If You post the color I will check my books fo some ideas.

[BuffaloGuy]

Thanks HowieE. It's purple.

[eazly]

Hey I'm having the same problem. I can't find the other end to connect this wire to. I thought that it was a black wire until I cleaned it off last night and found that it is a purple wire. I also tested to see whether it was a ground or had power on it. I found that I has 12 volts when the switch is on? Where does this wire go????? I've been having lift pump and glow plug problems since I installed my new engine. I think this has something to do with my trouble. My wire was also connected because I can see where it was once connected inside the plastic connector. :confused:

[BuffaloGuy]

eazly. Sounds like we're in the same boat. As I mentioned the other part to this wire was pretty hard to find. It comes out of another loom that comes up from below and crosses over the bell housing (at least that's what I remember). Both are purple. Pull off your 6.5L cowling (if it's even on) and stick your hand between the firewall and the motor/trans area and fish around some. That's how I found it.

I didn't check mine for power. Now I'm really wondering what it does!
Ken

[eazly]

Do you have lift pump and glow plugs problems? :confused:

[BuffaloGuy]

I've got a fuel pressure gauge plumbed in full time. No lift pump problems.

However, the motor has been hard to cold start ever since it was installed. I've replaced the glow controller, all the glow plugs and even installed the resistor (per More Powers recomendation) and a manual puch button to extend the glow time. It still starts like crap when it's cold.

I've taken apart the IP and checked the timing advance valves. Found some junk and cleaned them up. No change.

I'm like you, I'm hoping that perhaps this wire has something to do with it. I plugged mine in and it didn't seem to do anything. So now I'm thinking that maybe a sender on one end of this circuit is bad. That and I'm just real curious what it does!
Ken

[eazly]

I replaced my glow plug controller last night and it did not solve my problem. You sound like you know alot about our glow plug system. I hope that you can explain how does the glow controller know when to cycle the glow plugs? If there is no inhibit switch how does it know when and when not to cycle??????????????

[BuffaloGuy]

I don't know that much about these. I'm kinda like a blind man in an elevator.

But, I do know that there is a sensor that senses the temp of the motor and somehow adjusts the glow time. I've heard there are 2 sensors but I've only found one so far (I think the '93's are different than the electronic versions). The one I found is on the heater crossover right in front of the motor. I've pulled the plug and one side of the two spade plug-in has power with the key on. Then, if I jumper wire it I get power to my IP at the advance valves.

So, if the motor is cold this sensor must close the switch and send power. However, I don't know where the glow plugs get their power or how they are timed.

Here's another that's got me wondering. When I push my custom glow plug switch it fires the glow plugs as designed but then when I release and turn the key on the GM glow cycle is shorted to almost nothing depending on how long I hold the button it beforehand. Something is goofy me thinks.

I called my dealer this am and he is going to pull out his wiring books and see if he can find what this purple wire does. After that, I think I'll learn the whole wiring for the glow plug system. I'm tired of feeling around in the dark!

Perhaps someone here has the answers.
Ken

[rjschoolcraft]

The 1998 Feature Articles reprint volume has the glow system wiring diagrams in it. However, it does not identify wire colors...

If you bought the reprint, though, you could study the diagram and the actual wires and figure the system out.

In older GM vehicles, a purple wire was used as switched 12 volt supply to ignition components.

[BuffaloGuy]

Ronniejoe, Does it have it for the '93's?

[DmaxMaverick]

For most applications, GM has frequently used a "universal" wire harness for like vehicles, with modifications for specific applications (gas/Diesel, auto/manual, etc). The purple wire near the firewall, IIRC, is for an oxygen sensor, or spark ignition sensor, which the Diesels don't have. Not sure what the lower connector would be for, but likely emmissions related.

In any case, a good look at a diagram will tell all.

[rjschoolcraft]

Yes.

The reprints have 3 articles on glow plug systems. "1982-84 6.2L Glow Systems", "1985-93 6.2/6.5 Glow Systems" and "1994+ 6.5 Glow Systems."

[cruzer]

Hey Buffalo Guy, Ive been watching your post on your cold starting problems and doing similar test as you except for opening the top of the pump. At intial start it would smoke heavilly miss and chug. After oil press was up, if I drove it, it would be laying down a big fuel cloud,it was running Fat. If it where a gasser I would think the choke was stuck closed until temps got up to around 160*-170*. I jumpered the HPCA and could tell there was a slight change in timing.
So I went to find a new switch for the coolant crossover. I findly found a good auto parts guy who could use a book instead of a computer. And found out it is a HPCA switch for 92-93 6.5td. Everybody else was trying to give me a coolant temp switch. I think the switch when cold has 12v
going in and out. I installed switch and now I turn key ON depress the acc. a little to allow
fast idle sol to engage and let up, the glow lite goes out, I turn key it fires w/minimal smoke & has high idle and no smoke after that. I can drive it down the road UNTIL.........the advance turns itself off, which is around 140*-150*,then it starts running fat & sluggish once again. til temps get close to 170*. My other sypmtom is, if it is warm/hot, & I turn it off for 5-10-15min and resart it, it will run fat until I start driving down the road and get rpms up. Then it clears up and runs fine. I think I need to advance the timing alittle. FYI

I have AC60G's w/resistor, new controller, pump turned up 1/8 turn, injectors and everything else. They all have about 10k on them.

Eazly, I too have wondered how the glow plugs know when the engine is hot. People have told me where the inhibit switch is suppose to be. Its not there. I rebuilt the engine & thought I forgot something.NOT According to the trouble shooting guide, it states something like 1984 had one IIRC. I gave up on this subject because my lite comes on when needed and not on when hot.
So it must work.

[BuffaloGuy]

It's beginning to sound like a lot of us 92-93 owners have the same problem. Cruzer thanks for the tip on the sensor. I think I'll pick up another and stick it in. After 210k it may be shot and it's any easy test.

I'm also thinking that perhaps my HPCA was on when the timing was set since I found a little junk it the valve seats. I've got to find the time to get the timing checked.

I'm willing to bet that's not it though. It just "feels" like some sensor or wire is not doing what it should.

[eazly]

Hey I think the glow plug controller senses engine temp internally????????? Just thinking out loud. 93's don't have inhibit switches and the sensor for fast idle is not hooked to the controller. The sensor is hot when below 120F. I installed a toggle switch on mine to allow the engine to warm up beyond the 120, because it still would idle rough until it was at normal eng. temp. Does anyone know how much voltage the lift pump should have on it so that it can run? Mine only has 6 volts when cranking and I felt it and doesn't run with 6 volts. I jumpered it out and it run fines with 12 volts. I wonder if anyone had this problem. I just installed my new engine and dying to drive it, but since my lift pump is not running. My engine surges and stalls etc... :confused:

[cruzer]

Eazly, if you have a toggle on the fast idle sol,then are also energizing the HPCA sol and running power thru the HPCA switch also? Did you put in some sort of diode? Did you just wire the idle sol separate? I could see keeping the cold advance and idle sol on till approx 170*.
It doesn't smoke when it activated. I do need to get the timing checked also.

[BuffaloGuy]

Eazly, it sounds like your lift pump is not geting what it needs. I'd suspect the oil pressure sending unit. It's on the back of the head behind the fuel filter. It's known for going out. Drop a new one in and I'll bet your lift pump will be good to go.

On another note, I just got off the phone with the parts guys and the dealership. He said his books only show the 1 sensor on the heater crossover. The other on the drivers side up front on the block is only for the gauge. He wasn't sure how the glow plugs do their thing but he said he will pull the wiring books out the next time I'm in town and we'll lokk them over. I'll report.
Ken

[BuffaloGuy]

Well here goes. I studied the wirng books for about 45 min. at the dealer today. Here's what I learned about the '93 6.5

The purple mystery wire I started this post looking for is for the 4 speed w/overdrive auto transmission. What it is exactly for I'm not sure. I have a manual so it does nothing for me. Sorry auto trans guys but my time was limited.

Next, the glow plug setup does NOT include a seperate sensor. It appears that the sensor that senses the temp. is in the glow plug controller itself. I didn't find an internal chart for the controller.

As for my problem of shorted GM glow times when I use my manual push button switch first. It appears that there is a wire that comes from the left bank of glow plugs back to the controller. This wire is precisely the one that More Power had us put the resistor in. I suspect that the juice this wire carries tells the glow controller when to stop. More Power had us add a resistor so it would take longer for the juice to reach the controller. Good idea.

However, adding a push button switch will really do nothing to glow time BEFORE you turn the key. Every second you hold the button in is just the same as if the key was turned. Both methods are slowly overcoming the resistor and affecting whatever is in the controller itself to stop.

But the push button IS useful for after the glow controller is done with it's stint. Then one can hit the button and get more glow, even when the motor is running.

But, I'm still worried what this does to the controller itself. Juice will be backflowing into the controller unless the controller itself has a diode in it. Anybody know if it does and if it safe to do this? If not perhaps we should add a diode.

Now onto the temp sensor on the coolant crossover. The book was a little fuzzy here. It showed the temp. sensor that runs the fast idle and timing advance on the IP (and that's all it runs, nothing to do with the glow plugs at all) is supposed to be on the block back right (passenger side) right behind the last glow plug. Mine has a pipe plug there, no sensor.

However, I know that my temp sensor on the heater hose crossover powers both the IP dodads. So all '93's must not be created equal.

My next wiring mystery to solve was what does the sensor on the front left (drivers side) of the block do? I'm betting it is the coolant sensor for the dash temp gauge and that's it. Anyone know? I ran out of time.

Sorry for the long post but hopefully someone will find it useful.
Ken

[cruzer]

Buffalo Guy,
You are correct, the sensor in the driverside head is for the gauge. I removed mine and installed the probe for my mech gauge. The gauge
in the dash doesn't work since the removal.

As for the sensor in the right rear head, I don't have one either. I was concerned until I read in the troubleshooting guide chapter 13, ?-93 glow plug system. The section on the inhibit switch said they started using 1 in 1984 and carried it over to 1985, then discontinued. I gave up on the hole deal figuring my glow light was working properly, hot & cold, which is what the inhibit switch does. I did replace my controller about a 1 1/2yrs ago. Recently I compared the part # GM gave me and the part# I found on TDP for 92-93 and they are not the same.

It now makes sense, I felt I was not getting enuff or proper glow time b4 and you confirmed it with how the 92-93 controller works w/no inhibit switch. I did put in the resistor and it works fine now, plus I noticed the 60Gs made the controller stay on longer b4 I installed the resistor.

[Bobbie Martin]

The front left sensor is for the temp gage. My guess is they moved the HPCA to the crossover sometime in 93. If it has two terminals and it goes to the cold start, it has to be the HPCA sensor. As long as its in the coolant, it shouldn't matter where it is. Be glad its in the crossover. Its a real PITA to get to when its in the right rear head! The electronic IP's have the coolant sensor in the crossover for the PCM.

[eazly]

THANKS BUFFALO GUY I changed the OPS and the lift pump ran like a champ. This solved my surging problem. Now on the the rest of my problems. I still don't have a home for the purple wire with the single spade connector on the fire wall. I have an automatic transmission w/overdrive. I must find out where this things goes. I still can't get my glow plugs to cyle and now I have a diesel leak coming from the bottom of my filter bowl. This leak started when I jumpered out the lift pump. I might have overpressure the filter housing and blew a seal. It drips about a drop per second. Anyone have a 93 w/overdrive that can help with this mystery purple wire. I will look on the tranny real close. Thanks Buffalo Guy.

[tbuck]

Eazly,
I looked at my '93 and found the wire you're talking about. I have an auto and it is connected. Unfortunately, I don't see where it goes so I can't help you there. But if it is for an auto tranny and yours is not connected, you may want to talk to a tranny place or dealership about it.

[eazly]

Thanks this is good info. I will call a tranny shop right now. Maybe they can tell me where it goes. I'll report back once I find out. THANKS