Thanks for putting me straight Scott.   Yes of course I meant oxygen sensor....its just because it screws into the cat.....duh!
    
Thats interesting that the single wire temp gauge sensor will drive the gauge wired for two wire sensor.  I really hope you are right:-)  
I encountered a very similar situation in a Volvo where that was not the case.

If there is any way I can keep the metal t-stat housing I would like to do so.    I will be trying out the single wire signal.

Thanks again,  Steve

On May 2, 2013, at 11:21 PM, Scott Daniel - Turbovans wrote:

> there is no such thing as a two wire screw-in temp sensor for a vanagon.
> 
> take your yellow/red temp sender wire and connect it to the single
> contact on your screw-in temp sensor.
> I think it will work just fine if you don't even connect the brown
> ground wire..
> I think that  goes to ground anyway ..
> but you can ground that brown wire .
> 
> can sell you a plastic 2WD t-stat housing if you wish, new.
> the metal one is better. Obviously.
> the plastic ones shrink, dissolve, and generally fail in silly ways,
> eventually.
> 
> Don't overthink it.
> 
> cat converter cable ???  No wires go to the cat.
> perhaps you mean oxygen sensor .
> that connector is easy to identify ..
> the green coax........that's 02 sensor signal  feed to the ecu.
> the double plug is 02 heat.
> anytime the engine is running you should see 12 volts there.
> 
> On 5/2/2013 8:12 PM, Steve Cotsford wrote:
>> OK  I think I have solved my mystery connector issue.   Dennis put me on the right track.
>> 
>> I have discovered that my engine is from an '86 syncro.     As such, it has a METAL thermostat housing and a temp gauge sender that just has one wire (fits like a nail head on the sender instead of a plug.     This sender screws into the housing.
>> 
>> The van is an '89 2wd and presumably it had a PLASTIC thermostat housing on the original engine.   It seems it had a 2 wire temp gauge sender as the wires in Bentley jive with this (two pin, red/yellow and brown wires).    The sender would have been held in place with an o-ring and clip.
>> 
>> What I need to find now is a two wire temp gauge sender that threads into the metal thermostat housing.   Alternatively, I need a plastic thermostat housing to take the place of the metal one, so I can install the sender that gets held in place with an o-ring and clip.
>> 
>> Does anyone know if in fact there is screw in two temp gauge sender ?       If there is, I believe it would be for a 1987-1991 syncro with metal thermostat housing.
>> 
>> Its confusing that both the temp gauge sender cable and the catalytic converter cable have plugs with same color wires (red/yellow and brown) as well as the same kind of connector.    Only the length of the pigtail differentiates them.
>> 
>>