Expect trouble with the SMALL red wire that goes to the spade lug on the back of the alternator. This wire is subjected to much abuse as it goes under the front of the engine, and isn't protected until much further back in the wiring harness. It may be broken or frayed at the alternator, under the front pulleys, or up at the 8-pin grey connector on the firewall. Treat it gently- and re-route it around the right side of the engine compartment, with all new quality wire if needed.
Another victim of the lousy wiring harness.
Note that it's also possible the large wire terminal had cracked or broken off. A new crimp-on end is all that's needed in that case. Disconnect the battery FIRST!! Fire is not a desired outcome.
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Rob Bareiss, New London CT ::: '87 244DL/M47- 225K, 88 744GLE- 209K, 91 244 183K. Also responsible for the care and feeding of: 88 745GLE, 229K, 88 244GL, 146K, 87 244DL, 235K, 88 245DL, 236K

check the brushes and the blue ground wire on the alt. always hook the neg of the meter to ground, shouldn't matter where, unless the battery ground is loose or broken. good luck, chuck.