I have a 92 Trans am 305 tpi car. that all died and in went a 350 with carb. computer is in tact for speedo and fan. it appears i have a switch on both heads. one near cyl 6/8 and one near 1/3. which controls fans? temp gauge was saying i was at 240 and thats a bit much for my comfort level and the fans never came on. so what bit of wiring did i disrupt? i didnt cut anything simply deloomed it and tucked it out of the way. how would i start to diagnose this? i dont have any of the ac hooked back up anymore. but i havent for quite awhile and it made no diference before.

its my understanding the ecm and relays control ground? can i just ground one of the wires so i have the fans on constantly? im not opposed to this. but im not totally understanding which switch is which. im checking my headers as theyve chewed through both of those bits of harness and required repair before however they are currently in tact since last repair

i guess i shoulda start this in cooling area. sorry everyone.

 

The one on the pass side is the switch for the fan. The driver's side one isn't a switch; it's the sending unit for the gauge.

Probably the one for the fan switch. It's dk grn w wht stripe. Hook it back up to the switch and see what happens. You can ground its center pin with the key On, and the fan should run. Assuming of course that all of ITS wiring is still intact.

 

what is the one on top of the intake for?

so the pass side head switch should have a dark green/white wire going to it? or am i cutting it out of the relay and grounding it? im assuming thats what you meant by i can ground its center pin for key on? or im not following.

it should be in tact but accidents happen. i didnt cut or yank on anything.

 

That's the ECM's coolant temp sensor.

Correct.

I'd recommend against it. It's hard to make wires work better by cutting them.

I'd also recommend against that.

What I meant was, once you find that wire and the connector on the end of it, you can test to see if it works the fan, by grounding the center pin. If it does then when you hook it back up where it belongs (i.e. the fan switch) your fan should then work when the temp reaches the switch's set point.

This is REALLY SIMPLE stuff. It's just a CAR, and it's one of the simplest parts of it, the electrical system. 90% of it nothing but battery and ground. Doesn't get much simpler than that. If somebody as stuuuuupid as me can work on one, surely a smarrrrt guy like you can do it too.

 

The fan switch in the passenger head only controls one fan. The second fan is controlled by the ecm, at least on my 91 Z it is. When I disconnected my TPI the only way I could get the second fan to come on RELIABLY was to connect a switch on the dash and turn it on grounding the wire at the second fan relay.

 

thanks @sofakingdom im definitely overthinking it. with the center pin grounded the primary fan does turn on. appears the switch is bad then based on that. which i believe some research has shown switches to make the fan come on at lower temps. so ill look into that. a curiosity i doubt is would an aluminum head change the operation at all? id think not since everything is grounded but maybe ive overlooked something.

@BBCSwap as for the secondary ill have to pull up a schematic. i dont love aux switches but maybe i just find a clean way to ground that one or have the primary trigger it once that one is working

 

Shouldn't make any difference at all. Especially not to the operating temp. Temp is temp no matter the material, as far as that goes.

There's nothing wrong with adding a manual switch to a properly working automatic circuit. Which is not the same as using a switch instead of the automatic one.Butt as we all know, whether we like to admit it about ourselves or not, the least reliable part of any control system, is THE HUMAN using it. Deliberately arranging your car such that it burns down if you forget ONE TIME to flip a switch is just about the very height of idiocy. Adding one though, so that the auto thing works right butt you can ALSO turn it on any time you want, is less harmful; at least, if done in such a way that the car's wiring isn't botched in that critical place. You would just add a wire that taps into the dk grn/wht wire, and grounds that wire when you want the fan to run.

Yes there are a variety of fan switches with various operating temps. There's one that gets mentioned on here alot butt I can't recall the part #. Might be a Wells TS155 butt don't quote me on that.

 

There are numerous fan controllers that you could wire into your current relays. You can set them where ever you want temp wise. I have dual fans and one is set to go on at 185 and the other is set for 195 but you can set them higher like most stock cars designed to do. If I had mine on a switch it would be bad, but there are people who can pull that off.

 

I completely agree with you both i dont want it fully manual really. i quite loathe unnecesary added swtiches. im just hoping to find a way to make both work but the primary is key. maybe i can have the primarys function trigger the secondary relay since i have no AC function to allow that to work based on my understanding. i am however atrocious at electrical so ill keep digging before i make that assumption

ill dig around on the switches, seems the jet and hypertech ones have discontinued. i have a summit 3/8npt 200 on 185 off flavor ordered thus far. maybe ill find something else that appeases me.

 

I have a 180 thermostat. I didn't see any point in having a 180 thermostat if the fans didn't come on until 230. I didn't want mine completely manual either. When I wired my switches I back probed in the plug at the relay so I didn't affect the original function. I did keep my a/c but after my TPI delete the a/c fan would not come on when I turned on the a/c which it did before the swap.

 

gray way on the other relay i take it? dare i ask what you back probed with or how?

 

I think it's the gray wire on the second relay. I pulled down the rubber piece on the wire end of the plug that plugs into the relay. Pushed my ground wire through the hole that the green/w white wire or gray wire goes through in the rubber piece and used a small screwdriver to push my ground wire up into the plug to make contact with the metal clip. Push rubber piece back in place. Connect wire to switch. Other side of switch to ground.

 

allright im back. i know yall say electrical is easy but this isnt making sense to me. new switch. car gets to 220. fans still wont kick on. trigger the relay to ground, it works. wonder if the teflon tape wont let it ground, ground the switch. no change. i dont get it.

 

Trouble shooting electrical can be a real pain. If your switch is listed for your car it will not turn on until about 235 degrees as per GM. And yes the teflon might not be grounding. I never use teflon on a switch that is brass going into cast iron. but that's me.

 

so i replaced the switch with one thats on a 210 and off at 185. that 235 thing is sketchy and i didnt like it. my heads are aluminum but are grounded on the same head to the back. i guess i could check that. its an npt fitting per my understanding but ive always known them to need tape or paste. i could paste it if that helps but id venture it leaks without anything. i thought this was medial stuff i knew well but now im challenging that.

 

I've got this same problem where the second fan won't turn on. Activating the AC doesn't call for the second fan like its supposed to.
Currently I have one fan wired to a ground switch like suggested above, but we really need both fans to keep these cars cool.

 

neither of mine will turn on. i dont have ac so i understand why the secondary works but i need a primary to start with. figured i could get that going and jump signal but i cant even make one work.

i agree primary is a simple ground switch it shouldnt require another but geez this thing is fighting me.

 

Yes it's an NPT thread. A lot of people use teflon.
I have tried several switches that were "supposed" to turn on at 180, 195, 210, 220 and maybe another one or two. NONE of them turned on when the mfg claims they should. I had one that turned on at about 170 and never shut off. The others turned on at least 15-20 degrees higher than supposed to. You might want to run the engine and let it get hotter to see when it turns on.

 

I think you both are starting to see why I added switches to both fans.

 

interestingly enough weve had a change in diagnosis. i thought maybe coolants not geting to it. verified 195* tstat and its orientation is proper. needed to reseal a bolt anyhow.

took the tape off the sensor and just added a bit of paste. checked resistance between back of head and sensor, as well as back of head and firewall. all is ok.

ground trigger wire for sanity and turn key on. no primary now. so thats new. check resistance between signal wire and green relay terminal. 14.7ohms? it was like that when it did work but im not certain what it means besides a guess that ground trigger is excited with key off.

as i check the list off what could have changed if it isnt working forcing ground now?

 

I don't know. I would unplug relay and plug it back in a couple times. Maybe bad connection. And try it again. Maybe try grounding the green wire at the relay and see what happens.

 

primary relay at pin e has 12v with key off but not key on. tracing all fusible links and fuse holders back all have power. not making much sense.

tried 3 other relays. no change

 

Mine does exactly the same thing.

 

Its been months and I still haven't figured it out. My next solution is to install one of those pre wired dual fan controllers with the temp probe.
Murray Climate Control 25 Amp 6 Terminal Multi-Purpose Switch 35879 | O'Reilly Auto Parts

 

i loathed this style personally im trying to avoid that.

 

By chance, did you blow either of the fusible links on the weather pack that comes off the positive battery cable?

 

ok since nothing has been making sense i started overr. pulled both primary and secondary relays. jumped terminal e and d which is power and ground. both fans turn on.when i ground the wire on the pass head sensor. the fan turns on. the key here is that the secondary turns on. its a gray wire so where is the green wire with white strip for the primary relay pin?

drivers head has the sensor with a plain green wire which is temp gauge. and whatever the other on the intake is. some sort of ecm. but where is the green with white stripe, it goes straight to ecm with no interruption correct?

then what the heck does grounding the secondary fan switch have to do with validating the primary? i feel like i went through a bit of goose chase.

 

This is a problem,...Pin "E" should be HOT at all times. It's possible the fusible link is OK when key is off - but not OK when the Key is ON. If this is still true than the fans will never operate when the car is running because the relays can't work without voltage on that circuit. I'm GUESSING this could be bad relays too,...... somehow cutting off PIN "E" when PIN "D" gets switched power. ( just sayin',... it's possible for multiple relays to fail the same way !) If you are loosing voltage on 'E' when the relays are both connected: disconnect both relays and then probe both relay plug terminal 'E' ports when the key is in RUN. Still no voltage ? ( relays not suspect, fusible link or wiring is suspect )

Here is a diagram showing Fusible Link "D" and everything it is connected to: Note: fusible link D only protects the Fan Relays.


Once you confirm that your battery cable and fusible link D are GOOD if you're still having problems, read on.......


The secondary fan relay signal wire from the head switch should be GRAY. The primary fan relay signal wire from the ECM should be GREEN/White. I don't remember exactly where each relay is mounted,.. but secondary relay has GRAY and primary relay has GREEN/White as it's signal wire. Your stock fans and cooling system is set to turn on the primary fan at 222 degrees so if your gauge is off just a little - it might cause some anxiety. The stock secondary switch is set at 238 degrees. ( I bought a low temp switch and now my secondary comes on just after the primary. ) These schematics are from a 91 Camaro shop manual for TPI, so they *should* be similar to your ride.





TPI cars used a 2 wire sensor (CTS) to the ECM for the PRIMARY fan that was mounted in the front of the TPI manifold. The switch for the SECONDARY fan is located in the pass side head. The sending unit for the gauge is in the drivers side head. If your starting over, start with verifying power and ground everywhere first; don't concern yourself with the switches until you are SURE that you've got power and ground everywhere as expected.

There's no indication in your posts that you've investigated the coolant in your car and verified the temp gauge readings. Since your starting over - I highly recommend it.

** a 50/50 coolant/water mix will boil over @ 265 degrees.

Get a coolant tester and test the temp your coolant will begin to boil. ( It's important that you have a good working radiator cap of the proper rating for this process: IIRC it's 15 pounds ? ) Disconnect both fans, start and run the car, feel the upper hose and make a note when the hose gets hot (when thermostat opens) and look at the gauge; It should read the same as your thermostat rating. If not then the gauge isn't accurate or the switch is 'off'. Let the car continue to run until you see coolant begin to boil over into the overflow tank and IMMEDIATELY make note of the gauge reading and shut off the car. Does actual boil-over occur when the coolant tester said it would ? Does the gauge match those readings ?? Now you KNOW things and can make adjustments. ( need a new gauge switch ? Maybe a replacement gauge ? Need to adjust your coolant mix ? Need another thermostat ? )



You converted your ride from TPI to Carb and I'm GUESSING that you are still trying to use the TPI primary fan temp sensor mounted in the intake somewhere on your Carb intake. In theory - that should work OK if all other related wiring is still intact. Seems like the secondary switch is in the pass head and it hasn't been proven to work. If I were you I would remove the ECM control for the primary fan and wire it the same way the secondary fan is wired.... independent of anything else with a simple coolant temp switch as the trigger; But that's just me ! (You could probably also install a basic VSS Buffer - like the TBI cars - and then remove the ECM completely.)

** For the record,.... I never use any type of sealant when installing a brass switch / sending unit. The Brass is soft enough to seal to an Iron head and I'm guessing the same will be true even for aluminum heads. ( never a problem on my aluminum head LT1 engines )

Now that you ran the car till the coolant boiled and know the exact coolant specs,.... now it's time to re-test and check for problems. After the car cools to under 180 degrees & you've made adjustments (if needed),.... reconnect the fans and start/run the car till the temp gauge reads 260 or boil-over. Did either fan operate ? If neither fan worked then - most likely - something common to both fans is suspect. (HOT at all times on both relays PIN "E", HOT in RUN on PIN "D" & GROUND for both fans @ G117, Pass side radiator. ) If only 1 fan worked then the things specific to that fan are suspect. (switch, wiring, relay, etc...) Keep in mind that the ECM will require the proper grounds at the back of the pass side head to be able to control the primary fan properly,..... G112 and G118. ( If you've painted stuff then BE SURE that all grounding points are bare metal !! )

** At the beginning of last summer I dealt with a VERY similar problem; the fans just stopped working and probing/jumping wires didn't get me anywhere. After much aggravation I found the problem by accident,......... an intermittent bad connection of the dual fan wiring harness to the engine harness. ( I bumped it with my hand as I was testing and the fans began to work !)

I hope this helps in some way !!

 

Wow, thanks John!

 

well finally some good news.... i guess my frustrations with the efi should have lead me to this conclusion first. I carb swapped this thing because the car just would never run correctly. i fought with the 305 before blowing up two from mistreatment. overall data logs and wiring condition suggested everything was fine. the ecm would communicate, write and so far but every once and awhile id have sporadic issues. the 350 tpi made those issues even more prevalent. carb swap it was. kept the ecm for fan control and VSS support. turns out after all this diagnostic, chasing wiring and so forth the issue was indeed the ECM. even triggering the fans on via ecm would result in nothing. hopefully the drac stays in tact for vss long term. i do wish it was still EFI however i feel better knowing what the problem really was before. maybe ill try something aftermarket in the near future.

anyhow in my diganostics i took the now new lower temp fan switch on the pass head, gray wire and at the relays jumped it (with scotchlocks temporarily) to the green/white wire. ground jumper at the switch and both fans come on. snip both the green and gray wire. made a new harness to run alongside the main since i painstakingly taped and loomed the main one tight prior and didnt want to open it back up. swapped my carb jets as a necessity, played around with mixture screws and it finally got up to temp, both fans turned on. thermostat open. everything is happy. including me! i left the rest of the factory relay stuff in tact. and now the pass head switch controls the ground for both to come on. YAY!

 

Can you confirm that I understand you correctly for the fix?
- Uou installed a new lower-temperature fan switch on the passenger-side cylinder head.
- Jumped the gray wire from the fan switch to the green/white wire at the relay.
- Grounded the gray wire from the switch and this caused both fans to turn on ?By running the gray wire from the fan switch to the green/white wire at the relay, you're connecting the signal wire from the fan switch to the fan relay. Then, by grounding the gray wire, you're completing the circuit, which will trigger the fans to turn on.




So essentially:

1. Gray wire (from the fan switch) connects to the green/white wire (at the relay).
2. Grounding the gray wire completes the circuit, causing the second fan to turn on anytime after the first is activated.

The switch itself controls when this grounding occurs, based on temperature, but manually grounding it (like in the test) will trigger the fans immediately.

 

the first portion of what you wrote was just testing my concept but:

EXACTLY,
-i replaced the switch with a lower temp unit, just because 220 is alot IMO.
-i then took a spade terminal (or whatever your switch connection requires) ran a new green and gray wire, loomed it and ran it towards where the relays reside tightly along the path of the existing harness (since i wasnt unlooming the existing harness i had just tidied)
-cut the green/white wire on the primary relay attached the new green lead to it. did the same with the gray wire on the secondary relay.
-to test, again ground the switch wire and turn key on. both came on.
-plug the switch back in. let it get up to temp and both came on when. i dont have AC so both are running at the same time by doing this.

ultimately the new wire colors dont really matter here
I also dont love hacking up harness so i left the old ecm control in the loom and kept it minimal. maybe someday ill do something different but for now im happy with it. i also have one relay controlling one fan and like that alot more than one relay controlling both.