Fan control relay

loose connection on the temp sender unit, broken wire to temp sender unit
low coolant level in the system/ air lock

Hi Eric:
Blower Motor is usually only in one of two different locations... the first is on passenger side, access under the hood or, second choice, under dash access behind glovebox.

In both cases the resitor will be in the duct that the blower motor blows through.

Hope this helps; also keep in mind that your feedback is important and I'll appreciate your time and consideration if you leave some testimonial comment about this answer.

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Please make sure that the trigger required for the coil to give out the High voltage to spark comes from the pulsating voltage at the coil LT( low tension).
So check for the make /break on the coil- on one side you will need the positive and on the other the trigger. Once this is seen then the distribution can be checked, check the HT wires and contacts in the distributor.

That should be radiator fan relay, open or shorted. If your radiator fan is working as it should, the code may have been stored before rad fan was fixed.

cooling fan does not come on at all

To access the blower resistor,carefully pull down the lower right under-dash panel.(Below the glove box) it it will be right next to the blower motor in the heater housing. it has a plastic connector with a few wires running to is, and 2 bolts holding it in the housing. I hope this helps

try changing the coolant sensor, check wiring to fans good, and also the fan relay.

Behind the dash. You will have to pull the whole dash assembly. It looks like a little radiator.

fuse boxes are usually under the dash on the driverside up by the brake pedal and another one under the hood driverside if the fuses are good it may just be you have to replace the fan because there is a relay in the fan that may have went out and check out a salvage yard for a good used one

Here is a link that will give you the timing marks. http://www.2carpros.com/car_repair_information/tec_info/1990/plymouth/sundance/1990_plymouth_sundance_timing_belt_diagram_marks.htm