how did you check them with a test light?
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For trucks built before 11/89 only, install a resistor bar kit (E9TZ-12B602-A) on the electronic glow plug control module, Figure 1.
This resistor bar kit causes an increase in the glow plug temperature before the "WAIT TO START" light turning off.
32 DEGREES F AND ABOVE
For trucks built before the 1991 model year, replace the electronic glow plug control module (FOTZ-12B533-A), Figure 1. This module is located behind the Crankcase Depression Regulator held on with two (2) bolts.
An alternative action to installing the module is described below. This alternative requires a modification to the starting instructions outlined in the Owner's Guide, 7.3L Diesel Supplement.
For trucks built before 11/89, install the resistor bar kit (E9TZ-12B602-A).
For all affected 1988-90 trucks, disregard the "WAIT TO START" on the dash and use any of the following methods during starting.
Method # X
The resistor bar kit and the electronic glow plug control module cause the "WAIT TO START" light to remain "on" for a longer time. Installing them will allow the customer to follow the starting instructions outlined in the Owner's Guide, 7.3L Diesel Supplement and bring the starting time to a more acceptable level.
If the hard starting condition continues, perform the following checks to rule out other possible causes of excessive cranking time. Refor to the 1988/90 Engine/Emissions Diagnosis Manual, Section 20, for service details.
OTHER ITEMS TO CHECK
thanks Tim, later