You may have triggered SECURITY.
What does the SECURITY lamp do when
you are trying to start the truck.
There are 10 kinds of people in this world; Those who understand binary and those who don't.
99 CREW LONG SRW C3500 work truck 199k+ mi. orig. motor & trans 4.10, modded engine harness, new oil cooler & lines, all new front end parts and poly bushings, trans poly mount, all new brakes.
96 SUBURBAN K2500 wife's truck 210k+ mi. orig. motor & trans, 3.73...
95 C2500 Suburban 6.5td HO w/p, timing set, HB & pulley, all rubber hoses, modded engine & main harness, converted to OBD2, PMD to bumper...
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96 C2500 Suburban 7.4L converting to 6.5td w/ DB2, 4L80, 3.73