Background:
Alright, so my dad and i recently swapped out a carbed 305 to a carbed 350 from a 72 monte carlo into my 87 iroc. Although there was a plan to do it eventually, it was kind of forced upon us once the 305 started knocking. Anyways, everythings going good so far with the help of this site and we're up to the wiring stage. As mentioned in the title, we have not firgued out the temp gauge, oil gauge, or electric fan.

Temp Gauge:
The 350 has a different type of plug located on the driver's side head with two green wires coming from it and doesn't match up with the car's single green wire. Then i tried replacing the sensor with the one from the 305 but the hole is too big. would an adaptor solve this problem? and is this the only wire that needs to go to the gauge?

Oil Gauge:
Well, this didnt even work before the swap but there is a plug on the back of the block under the distributer. When it is unplugged the gauge remains at its highest. When it is plugged in the gauge just resets itself and then goes back to the high position with the start of the car. Will i need a different sensor? Is this the only one that needs to be connected to make it work? i was reading something about another sensor by the filter...

Electric Fan:
I havnt really found much out about this one except that i know it worked before the swap. Is this related to the temperature gauge on the side of the head? Will that solve both problems? Another sensor i dont know about?

Any info on any of these topics are greatly appreciated. Im assuming that a lot of the trouble is just the 72 to 87 wiring swap even though they are both SBCs.

Sorry for the long winded-ness. Thanks again.

 

Here are some pictures to help out. Sorry, they're phone quality. Please correct me if im wrong.

Any feedback is welcome.

 

ok, first things first, your pictures, yes that's the temp sensor, yes that's the oil sensor, and I don't think that's your fan switch. I believe that is a low coolant sensor. The fan should kick on when the temp sensor in the cylinder head reaches a certain temp. the fan should always have 12v running to it, and the ground should be going to this temp sensor, once it reaches a certain temp the sensor grounds to the head and completes the circuit for the fan turning it on. not sure what the temp should be for a stock guage, I've got an aftermarket switch that works at 180. In my opinion you should go aftermarket on your guages anyway, the stockers aren't as accurate now as they were 22 years ago, especially since you swapped the motor.

 

Alright, so here's the follow up that i should have put up a long time ago. Sorry.

Oil Gauge:

I've given up on fixing this for now. Not sure whats wrong with it, couldnt seem to find anything near the oil filter that looked like there should be a plug to.

Temp Gauge:

Used the original 87 stock sensor on the drivers side of the 305 block but had to buy a fitting to put it into the 72 350 block. Used a clip to attatch the green wire to it. Been working pretty well ever since. (See picture for help)

Electric Fan:

This now turns on by ignition. A lot of trial and error but finally got it to work. Hopefully this'll save some other people some problems. This is safe because it runs off of the original circuitry. Just look for the fan relay box. Cut the green wire, not too close to the box though, and then join both ends of the green wire to another wire. Mine happens to be red, and then have that wire grounded. I grounded that wire to a bolt. Basically, the green wires are still attatched but you're adding a ground in the middle. Works pretty well, the car hasnt even gone over 180 yet since the fan is always on when the car is on. (See picture for help)

Only problem I see is that i can't just sit in my car with the keys on to listen to music, etc. because i think it would drain the battery pretty bad. I could just be paranoid/have a bad battery though. Eventually im going to buy an optima and not worry about it.

Anyways, hope this'll help some people out.

 

If you wanted to sit and listen to music in the car you could just turn the key backwards to the ACC power position, assuming it works correctly still. also, you could put in a fan inturrupt switch that will kill power to the fan(make sure to relay it if you do this people.) that's what I had in my 84 TA.

 

I just ran outside to check it out right when I read that and you were so right. Thanks so much. Turn the key backwards and no fan haha cant beleive I didnt know that.

I used to have a physical switch on the inside of the car but it just got too annoying to use. The little setup i have just basically grounds the fan imediately instead of waiting for it to reach a certain temperature because for some reason that didnt seem to work very well for me.

Honsetly, the car used to have an overheating problem but this keeps the whole thing a lot cooler and with what you just told me there doesnt seem to be much of a downside.

 

Glad to hear everything is working out for you.