Which of these plugs should I use for 620 aftermarket temp gauge?

[antiextreme]

I see two potential spots on the lower thermostat housing to use for my aftermarket temperature gauge.  Any ideas which one to use?  Also, if I decide not to use the gauge but just choose to run the stock gauge in the dash can someone please tell me which wire attaches to what I assume is the sending unit (that is, the lower plug that doesn't have anything attached)?  

 

During a head rebuild I forgot to mark a couple of things.  Oops.  I have to wires that look like they could potentially be plugged up to the sending unit, but neither of them seem to move the needle on the gauge.  Is there perhaps another wire that I missed?

 

[dat521gatherer]

That wire goes on the bottom left sending unit. You can ground the wire on the engine or body and your needle should move to the hot position in like 10 seconds or so.

[dat521gatherer]

I like to run both the stock gauge and the aftermarket.

[datzenmike]

 

The top one with the two terminals can come out. I had one like it on my 710. I believe it's a thermal vacuum switch to allow full vacuum advance only when the engine is warmed up. If the wires go just forward to something with a vacuum hose to the distributor, that's what it is.

 

The '74 620 shouldn't have this so maybe the head or the thermostat housing is from something else?

[antiextreme]

I think you are right. There are several things on this engine that I found to be uncommon to the 1974 620. This housing is probably one of them. In fact, I think one if not both of these connections that I have in my hand attached to the old Hitachi carburetor and the now discarded EGR valve. Would just really like to get that temperature gauge working.

[Eagle_Adam]

The wire to the temp gauge should be a single yellow wire if memory serves me right. Bullett style connecter pops onto the lower of the two temp sender lookn gizmos

[Eagle_Adam]

The yellow wire ur after is in the dizzy wiring part of the loom

[datsunaholic]

The top one with the two terminals can come out. I had one like it on my 710. I believe it's a thermal vacuum switch to allow full vacuum advance only when the engine is warmed up. If the wires go just forward to something with a vacuum hose to the distributor, that's what it is.

 

The '74 620 shouldn't have this so maybe the head or the thermostat housing is from something else?

 

Actually, '74s did have that.  It's to disable the EGR when the engine is cold.  '73s had it too, to disable the 2nd set of points when the engine was cold.  Both were for the emissions reasons.

 

'75 and later used a completely mechanical thermal vacuum switch instead, to eliminate the vacuum solenoid, which is why you usually don't see those temperature switches on L20Bs.

[datzenmike]

Doug I found and lost the reference to this being on California equipped 710s. My Canadian sedan doesn't have it but my '76 L20B from Nevada does.... and yes it may have been a vacuum line to the EGR. I removed it to replace the thermostat housing with the broken bolt(s). No loss really runs just as good without it.