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Stock Sending Units

M

mr_blasto

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Nov 8, 2004
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Hey guys,

I am just about done swapping a 400 in, but I am having a helluva time figuring out the sending units for my gauges. I have temp, volts, and oil pressure, and based on the two trucks at the junk yard from this era, this seems to be a fairly common setup. The gauges didn't work when I bought the truck so I can't really compare to the setup on the previous motor.

My best guess is there is a temp gauge switch/sending unit on the drivers side in the head near the front of the block and a temp light switch/sending unit on the passenger side of the head (this one has a blade like connection). Is this right?

For the voltmeter, my best guess is that the sending unit is built into the two pronged plug that goes into the alternator. Is this right?

Now oil pressure, this one seems especially tricky. Seems this would go into the block. There just happens to be a plug right by the oil filter area so I would think a switch/sender could be mounted there, but the sending unit I figured was the right one is way too wide to fit there (the lip on the end of the block getins in the way.). Which then made me wonder if it was a remote sending unit, like the reading comes from there, but some hose/line of some sort is run to get it away from the block... but this doesn't sound so stock. Any idea where this sending unit hooks up to?

Locations for any and all sensors would be great, and part numbers would be fantastic as well. If anyone wants to go crazy and take some pictues, well... knock yourself out. Admitted noob looking for a little guidance.
 
The temp sender mounts in the left cylinder head, carquest #85208. Originally the 72s had 2 senders one for the gauge with a button style connector and one for the transmission controlled spark, with a spade connector.

It should have an ammeter not a voltmeter, and it wires in in a way that is hard to explain and understand, they usually don't work anyway so don't lose a lot of sleep over it.

The original oil pressure gauge is mechanical and uses a copper line from the fitting right above the oil filter to the back of the gauge.
 
BigBlock, thanks for your response--they are always very helpful.

Transmission controlled spark? I have never heard of this before. Why? How does that all work, or could you point me to a resource that explains how this system works.

I won't lose a whole lot of sleep over the ammeter thing, but it would be cool the have the factory oil pressure working. If I don't have the tube, could I order one or is this something I would have to bend up (which isn't likely to happen). I suppose after a 1" body lift a stock tube wouldn't work.

Do most people still have the stock oil pressure gauge working? Has anyone figured out a work around? I suppose with a mechanical gauge there is really no way to work around the oil going up to the gauge. Is their any sort of flex fitting in the tubing? For some reason it seems like this setup would be less than ideal for
our applications.
 
You can make a new tube out of 1/8" copper easily enough. Originally the line had a small coil back by the distributor to give the line some room to flex.

I need to correct myself on the connection spot on a small block. It connected at the back of the block by the distributor. The big blocks connected above the oil filter. It doesn't really matter where you connect it, I just want to be accurate with my info.

TCS is a pretty simple system, all it would do is turn off the vacuum advance until the engine reached a preset temperature and was in high gear. It used a temp sender and a switch on the trans to run a relay or two that mounted on the firewall and the relay would turn on a solenoid to allow vacuum to the distributor. There a few variations on this system but basicly that how most of them worked on the 71-72 trucks.
 
Thanks a bunch. I know the exact coiled line you are talking about back by the distributor. I didn't know exactly what it went to but figured I would swap it over anyways--so I am good there. Woot for working oil pressure gauge.

My current motor has plugs in the whole where the temp switches go. I think I got the right stock replacement switches, but the hole they go into on my new heads is a bit smaller than my old heads. I have to hunt those down now.

I know you are running TBI on a 400. It was my understanding that my ECM would be controlling the advance and all that (using an HEI ignition on the new motor), so do I even need to worry about the TCS? My last distributor was an MSD, and I didn't think it had the vacuum advance function, so I don't have an old distributor to compare my HEI to.

I am hoping to fire this thing up tomorrow afternoon/evening.
 
I haven't seen a functioning TCS system in 20 years, it was purely to control NOx emissions. I'm sure most of the parts on your blazer were thrown in the garbage while we were still in diapers.

The ECM will control spark with the right distributor so all of this is purely trivial.
 
do you happen to know of any 3/8" temp sending units with the button type connection and a similar calibration to stock? I figure it is a stretch but you might. Is it possible to just use a 3/8" to 1/2" adapter?

I remember looking the a catalog at autozone or something where they had the resistance range and corresponding temp range for a bunch of temp switches--maybe I should go bug them again.
 
ts-228 is the closest I can find. It's an 1/8" fitting and you'll probably have to special order it.

I usually tap the head for 1/2" NPT and reuse the original sender.
 
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