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Needed some advice on how to test the cruise control servo on a 1985 automatic L98 motor. I replaced all the vacuum lines, including the hose from the servo thru the firewall and to the brake switch. I get vacuum from the manifold on the other hose. The servo gets 8 volts on terminals B & D with the ignition on and cruise control powered up. I would like to check if the switch that sets the cruise speed is working properly by checking for power to one of the other servo wires while hitting the set button and driving over 30 MPH. Does someone know which terminal of the servo connector should be tested?
Hi
Don't forget to check the brake switch without any vacuum hoses, i had the odd cruise drop out on rough roads.
Turned out the electrical brake switch which has a dual switch was faulty, the metal strip inside broke making a poor contact.
The cruise control works not only on vacuum, check the switches too.
Long shot here as well but check to make sure your cruise cable is still attached to the diaphragm. I couldn't figure out why mine wasn't working and just happened to remove the boot that covers it. Sure enough, the clasp (like what you have on a ceiling fan pull down cable) had broken.
Here is what my 85 FSM shows for diagnosis. TLDR is; if vacuum, chain, grounds and fuses are good pull instrument cluster and perform the voltage/ohms checks there and check ohms at servo.
Testing cruise on 1985 l98
