Background: Truck not starting; starter or relay was clicking; guessed it was relay & replaced it & recharged battery. NOW – starter doesn’t turn, when ignition key is turned Tachometer reading drops below zero and sometimes pulses. I’m thinking something not wired right (reversed something?). Relay has 4 posts & uses 3. One for starter cable; one for ignition lead; one for battery positive cable and a collection of other small wires connecting to who knows where. Looks to me like the same as what I had on the old relay.

If you are pretty sure no wiring is messes up then I suspect the battery. A strong jump would prove this and any car battery can fail - in different ways. Holds a charge but no amps or just plain quit. They don't all age well. The starter will just flutter with less than enough power. You need to test out that battery for amps or if old it's junk. T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/