Originally Posted by Billybob

On 126 chassis vehicles there is a coolant heated heat exchanger inside of the lower windshield, this warms the lowest part of the windshield preventing an accumulation of snow or ice that is swept there by the wiper motion.

It can be disconnected without too much of a problem, the only issue would be to close or plug both the coolant feed and return lines to prevent the loss of coolant. There is a thermostatically controlled valve which controls the coolant flow into the heat exchanger. This valve and the associated hoses are located beneath the cowling which also covers the wiper transmission.

You can disconnect the small inlet hose from the heat exchanger and loop it back onto the return pipe bypassing the heat exchanger completely.

In your case it sounds like you will need to get in there and plug the return line so as to prevent coolant loss from it and the new incorrect line without a heat exchanger inlet opening doesn't need any sort of plugging.