When you say the heater doesn't work, you mean it blows air but it's not hot?
I don't have any pics, but I'm betting it went something like this, if I understand you correctly:
Heater core started leaking all over the passenger side floorboard, so rather than fixing it right, they cut the heater hoses and tee'd them together.
Take a piece of your heater hose to the parts store and ask for about 10 feet of it. IIRC, the upper connection on the passenger side of the water pump goes to the upper connection on the heater core. Lower to lower.
If you discover you've got a leaky heater core, don't freak out. on the '87-91 trucks, they're easy as hell to change.
EDIT: Damn, Bri_Guy beat me to it.
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