[LemmyThe1972Wagon]

so, i just replaced the hacked up wiring in my 1972 lemans wagon. i replaced the dash wiring with new M & H wiring for a car with gauges and A/C, a new printed circuit for an early build '72 with gauges(car built in september 1971), and a new M & H engine harness for a GTO with a V8 & A/C and points type distributor.

my turn signals now flash on my speedo, my hi beam indicator light works, and my gas gauge flickered when i turned on the car after completing everything, so that gives me just a tiny bit of hope that i may now finally have a working gas gauge. i don't know about that yet, as i haven't driven the car yet because the replacement remanufactured 2 bbl carb just arrived today(a whole other story and issue there). i've only looked at the car during the day as well, so i don't know if the dash lights work as far as illuminating the gauges go. i have no reason to believe they don't work.

now, my question is: how do i hook up the oil pressure sending unit so i can have a working oil pressure gauge, and the same goes for my water temp. how? my car was originally an idiot light car, so i already removed the old oil pressure switch, and replaced it with one of those 45 degree brass elbows and those large oil pressure sending units, but there's no response on my dash, plus the only way i could get that elbow tightened all the way was to have it pointed straight down, which wouldn't have allowed me to attached the rest of it. i haven't seen any oil leaks at all so far, and i've let the car idle. the unit is tightened in the elbow, which is kinda loose, and allowing the sending unit to rest on the TH350 transmission cooling lines that go to the radiator. again, i haven't seen any leaks.

the water temp switch is still in the passenger side cylinder head, and it's the one for idiot lights. i went ahead and got the rally gauge temperature extension while i bought the other harnesses, but i can't figure out how to hook it up. i have a sending unit for gauges mounted in the intake where that emissions thing normally goes, but the old emissions things was broken and i had no idea what it did, so i swapped it out for the temperature sender.

one last thing: even though my alternator is charging the battery, my GEN light is on and won't turn off until i shut off the engine. any ideas there? there's also a yellow wire that leaves the harness at the same place as the alternator wires. i don't know what it goes to, so i just used electrical tape to tape it back to the huge stalk of wires leading to the alternator. maybe it's for the idle solenoid on a 4 bbl, since the harness is for a GTO with a 4bbl and A/C?

i have some pictures of the yellow wire near the alternator and the water temp switch/ new sending unit just in case they would help.

[PB]

Alright, here's what I know. Been messing with this myself for quite a while now.

The yellow wire does goto idle stop solenoid on the carb. In pic #3, that is not the right location for that temp sensor. A thermal vacuum sensor goes there, where your carb emissions vac lines goes into it and then a vac line out the top goes to your charcoal cannister. It's a 72 only part and hard to find. that sensor shown, goes on the drivers side Head. If you had idiot gauges, there would be a plug with a square or hex indetion to get it out.

NOW, what I know of M&H, is I think they have their wiring messed up for 1972 w/ ralley gauges. I bought a new one YEARS ago and it came with a separate harness. I told them at the time that was incorrect and sent them a wiring schematic from the service manual as well as sent in two old wiring harnesses showing the proper routing for the green wire that attaches to the temp sensor on the drivers side. They were very helpful and sent me a new harness as I specified...but they stated it wasn't factory and was a modified harness. Which, it isn't. I was looking thru their cataloge this summer and saw that they still listed that green wiring harness separately if you have ralley gauges. That is wrong....is the green wiring not in your wiring harness?

So, my guess is the green wire is not incorporated into the main wiring engine harness like it should be, am I right? I will post pics of how to hook all this up.

[PB]

proper hook up with correct smaller loop holder:

Green wire feeds back into main line that goes across the intake and back to the fuse box.

[PB]

Picture of correct thermal vac sensor hookup:

[PB]

Far as your temp sender on the pass side, in your first pic above....did that one have one or 2 prongs? If it was idiot lights, then you need one with 3 prongs.

[PB]

The blue wire with single connection (like the yellow carb wire) hooks up to your oil sending unit on the back side of your oil filter. Not sure if that elbow you describe is hurting that or not, see pic below. That runs your oil pressure.

The one with a fuse type resistor connected to it, goes to the TCS switch as seen in the below pic..the one just forward of the red hose with the vac lines attached to it on the side and the back.

[LemmyThe1972Wagon]

the green wire for the temp. sender does not exist on my wiring harness. and the water temp. switch in the pass. side of the head has 3 prongs, it came with the car. keep in mind i want gauges here, i just haven't removed that piece because i don't want coolant flowing out of the head. i have an automatic, so i don't need to hook up the TCS, i need to hook up the SCS instead, but i first have to replace the speedometer gear housing on my trans since i accidentally broke the old wire trying to take it off. luckily, i have a back up TH350 sitting on my back covered porch, so i just need to wait until i have the time to get around to it.

[PB]

Here's a thermal switch that will work:

http://forums.maxperformanceinc.com/...d.php?t=679930

[PB]

Can you post pictures of your harness? Is the ralley gauge harness a separate harness then? I'll post pics of two original wiring harnesses that came from 1972's with ralley gauges. Both have the green wire set up in them. One is the harness i sent to M&H. I still have the harness M&H made for me that is the correct way. I'm surprised they haven't had more problems or people with questions as it sounds like they are not sending out correct harnesses for that application. I know they have told me they are going by factory documents, but not sure which one they are using for the ralley gauges...it's not for a Pontiac lemans with ralleys anyway.

First two pics are of the M&H one I have they built for me that is correct for 72 w/ ralley gauges and AC and non unitized ignition. the rest are pics of originals w/ ralleys showing the green wire.

[LemmyThe1972Wagon]

i'm not really worried about that thermal switch at the moment, so i won't mess with that. my harness from M&H is exactly like the one in the first 2 pics EXCEPT for the green wire that goes to the driver side cylinder head. i notice that the harness has the 4 wire connector for the temperature switch on the passenger side of the head as well as the one for the driver's side head gauge unit. wouldn't having 2 different temperature sensors screw up the gauge somehow? maybe the gauge unit uses a different connector or something than the pass. side head switch, and that gauge one was left empty at the fuse block connector? this car is my daily driver now, so i'm not going to tear apart the harness now, but i'm working on getting another car and once i do that, i think i'll custom make a wire and try to get it hooked up myself. i've got the '72 factory service manual, so i can see the wiring diagrams for all models; it shouldn't be too hard. i just need to make sure i've got the right size wire and right length.

so, we've somewhat got the temperature sensor figured out, i just need to actually make the wire since that'll be much cheaper than having M&H custom make one for me. for the oil pressure sensor, like i said, the brass fitting is loose, but i think this weekend i'll try removing that brass elbow and installing the unit without it, to see if that works.

i also would like to know, when i turn on the car, what should the gauges/lights do? i know the ignition key buzzer will turn off when i crank the car and the engine starts running, but are the gauges supposed to move when i insert the key or when the engine starts? are any lights on the gauge/speedo cluster supposed to light up? like i said, my GEN light stayed on constantly when i last started the car after doing this wiring swap, and i'm pretty sure that the light is only supposed to come on when there is a problem with the alternator. my brake light also did not come on at all. i'm unclear if the brake light is for when my parking brake is applied or for if i have low fluid or low pressure in the brake system, maybe someone could clear this up for me? if the light turns on, does that mean i have low fluid or pressure, or does it just mean my parking brake is applied?

[F ROCK]

i think all the gauges go to zero, exept fuel, when the key is turned.
the brake light indicator indicates fluid pressure, not e brake on.

[LemmyThe1972Wagon]

alright, that means my brake light could be working, could not be. i had the car's brakes power flushed when i had the power brake booster replaced in september, so it's got plenty of pressure in those lines.

my oil pressure and water temp gauges don't move when the key is turned or when the car is started and running. could this be because i don't have either gauge hooked up to the engine harness on the engine wiring side of the firewall?

[Forrest]

Originally Posted by F ROCK

i think all the gauges go to zero, exept fuel, when the key is turned.
the brake light indicator indicates fluid pressure, not e brake on.

when the e brake pedal is pushed down the light SHOULD come on...when the pressure is low the light will come on when the brake pedal is pushed down.

[Loffen]

Would it be an idea to buy the shop manual and check out the wiring diagrams there ?

To me it looks like most things was messed up when you tried to replace the original harness, usually there is no problem to repair a hacked original harnes and if you do not have the wiring diagram or can not understand a wiring diagram just stay away and let someone else repair it.

I do not mean to be grumpy, but I have lost the count of how many cars I had where some one tried to fix the electrical system and made h*ll cold, the rule is simple, if you do not know how to do it, dont...

Anyways, if you had the original wiring and wanted gauges you would only have to change posision on two wires at the conector to the cluster.

And rule # 2 if you are doing an engine swap or simular stuff take pictures before you remove anything they when you forget (Yes you will forget something) the placement of a connector or what ever you can allways go back and check it out.

[PB]

Originally Posted by LemmyThe1972Wagon

so, we've somewhat got the temperature sensor figured out, i just need to actually make the wire since that'll be much cheaper than having M&H custom make one for me.

M&H took my harness back, built it like it should have been in the first place, and they did it for free. They have great customer service. I thought when I went through this years ago that they would adjust the way they built harnesses for 72 pontiac A bodies with ralley gauges. Guess not. Don't know how long ago you got your harness, but if you just call up and tell them it's not what you want, I'm sure they will do what they can for you. Shouldn't cost you extra.

Far as I know, you need both those switches to have the temp sender work. You can't have only one plugged in and it work. Not up on the wiring part of why that is, but I know one won't work with out the other. Another 72 only thing.

[Forrest]

I have a '72 service manual and will look at the schematics..

[Loffen]

Again sorry for being grumpy

I was just back from the Paint/repairshop where I am going to paint my car and the owner asked me to help in out on his -96 Chevy van.

Hi had the ABS lamp glowing and comming on and off, after 4 hours of checking codes and sensors he told me that two of his so called mechanics had changed the diesel pump a couple of months back.around the time the ABS lamp had starting getting funny,,
Anyways they had used 4 full working days trying to figure out the ABS lamp, with no result, it took me an hour to find the two ground wires the idiots had forgotten to connect to the engine block...

Back to your case, the schematics in the shop manual are just like a road map, you will not find the right way without it, PB has done a great job helping you and I think Forrest will do what he can to help you to, that is why this forum is so great, dedicated people will allways try to help you out.

Then you have oddballs like me that sometimes goes over the top after a bad day

[LemmyThe1972Wagon]

i have a printed original copy of the 1972 pontiac full-line service manual, the 1972 fisher body manual, and a copy of the service manual on my computer with the '67-'76 firebird parts catalog. i've got the literature i need, and i just finished taking my second electronics course at school (UTI).

so i have the knowledge and tools, i was just trying to figure out where the pressure and temperature switches should be and how they should be hooked up. i'm going to do some work on my ignition system this weekend because the car's misfiring so badly i had to up the idle speed to about 1,500 when hot, plus i've got to replace the starter, which finally died after 2 years of being a daily driver, i'll take this opportunity to compare the wiring with the wiring diagrams and see if i can figure out what i need to do. it's always possible the brake light could have a burned out bulb, after all.

besides, the reason i replaced the engine wiring was out of necessity. i just figured i'd upgrade while i was at it. the old engine wiring was cut and spliced, had no insulation at some places, only the copper strands. the starter only had 2 wires going to it as well! one wire was cut, one was cut and respliced, but very poorly, and the battery wire was bent pretty badly. quite honestly, i'm shocked the engine was even running for the past 2 years. since i replaced the engine wiring, the starter sounds much, much stronger now, even though it locked up yesterday, causing me to smack it with a wrench to get it going again. i figure i'll replace it now before it dies at school when i have to go to work or something like that.

[Loffen]

Ok, then you have to try to find the right wires in the engine compartment.

Here is the easy way, it may take some time but you will find the right wire if it is not cut.

Connect an ohm meter (or whatever you call them where you live, nice to have one that says BEEP when you put the black and red wire togheter) make an extension wire from the meter that you hook up to the oil pressure gauge at the rear of your cluster, you are looking for the lead at the print board that goes directly to the connector, not the one that are common to the other gauges.

Then you take the other wire on your meter and check every wire in the engine compartment, when it says BEEP or give you a full ohm reading you have found the right wire.

Remember to have the ignition switch on, you do not need to have the battery connected.

[LemmyThe1972Wagon]

okay, my digital multimeter has a voltmeter, ohmmeter, and ammeter, so i'll give that a shot and see if it helps me out.

for the brake light, i'll replace the bulb and see if that works, if not, it could be the parking brake switch, because my parking brake doesn't even work right, so that may be affecting the switch's function.

and for the water temperature gauge, i'll probably just wait on that, because i'm actually more concerned with oil pressure at the moment than anything else. the engine being as worn out as it is, i'm more concerned with the engine having catastrophic failure than the coolant getting a little hot.

but the question still remains: why does my GEN light stay on at all times? shouldn't it be off normally and only turn on when there is a problem with the alternator or other part of the charging system? it's obviously not a burned out bulb, and everything else appears to be working fine.