Coolant sensors

Guys - As I've been "peeling the onions" on my '85 F150, I'm down to the dead coolant gauge.  Having replaced the little snap-in voltage regulator on the cluster, I have oil, charging and gas readings fine but no movement with the temp.  When I bought the truck, things weren't hooked up and the harness had been butchered, so I'm going to ground the sender wire and see if the needle moves today.  At least I think it's the sender wire.  
Thing is, there's a nice new-looking two wire sender coming off the water pump and there appears to be a single wire sensor at the rear of the block.  Does it matter which one I use?

Yes it dose.
The front wires / sender are for feed back to a computer, feed back system on the truck at 1 time?

The gauge sender should on the block, right side rear under the manifolds.
Should have only 1 wire, dont know the color soory
Dave ----

Dave - No wonder I don't get a reading!
My truck was originally fuel injected and a p.o. removed all computer stuff and installed a carb.  So, I'll run that wire to the block sender and just plug the hole on the thermostat housing.
Thank you so much!  Geez, I love this forum!

what year truck and what engine? I was under the impression you had the 1985 4.9.

I have an '85 F150 with the 4.9 six - and Ford didn't make things any easier when half the fasteners are metric and the other half are SAE.  Grrr!

someone correct me if I'm wrong but 1987 was when the 4.9 was introduced with efi. all carb up til then

what I'm saying is "stop fixing until you know more" the two-wire temp sender in the water neck/ heater port is for the eec . the temp gauge sender is a simple brass one wire unit with a threaded stud which normally will have a small black 90 degree plug that just slips on just like the plug that goes onto the oil pressure sender or even the signal wire on the starter solenoid.

mat in tn wrote

someone correct me if I'm wrong but 1987 was when the 4.9 was introduced with efi. all carb up til then

1987 is correct. He was swapping an EFI head on to the engine a while back, I do remember that. In 1985, the only EFI was the 5.0, and even then, it was only some of them. I think the 5.0 finally went all EFI after February of 1985. The 300 might have had a feedback carb in a 1985, but it definitely wasn't EFI until 1987.

that's what I was thinking. in an earlier thread I think there was a bit of discussion about which cyl. head was on the engine as he was putting the manifolds back on. anyway, the point is that the truck was most likely not a fuel injected truck ever. therefore, everything for it to be a feedback system should all be there.
eec box under the dash above the gas pedal, thick film dist, single wire o2 sensor, tps on carb, and two wire temp sender.  there should be the three wire plug for a tps dangling at least. and there should be a two wire plug right at the top of the valve cover near the carb for the bypass/lean solenoid.

It's cornfusing to me too, Matt!  My truck's been butchered to the point I've named it Frankenstein!

very often these trucks have been "fixed" a lot by the time the restorers get them. I'm guilty of modifications too.  the truck I'm doing now is getting modified but I'm building it for me so no big deal. but I like to modify by using the best that FORD offered even if it means as new as 1996 when it comes to parts. I'm not interested in a basket full of aftermarket parts.