Have been having intermittant starting problems with my 97 V8 4.6L F150 90,000 mi. - doesn't happen all the time. When I turn the key, I hear a single click and the lights flash off for a moment, but the starter motor does not activate and the engine will not turn over. The battery is fine as evidenced by the lights, etc. working fine. I did trouble shoot the starter relay (mounted on the firewall) by disconnecting the ignition signal wire coming into it from the ignition switch, and then connecting a jumper wire from the + battery terminal to the bare relay post. The starter motor then tried to operate. This would lead me to believe my relay is ok. However, sometimes when the truck won't start, I've tried removing the same wire, cleaning the terminal, and replacing the wire and the truck would start right up just by doing that. This lead me to believe it may BE the relay, or the ignition signal wire itself. Then the other night it wouldn't start, and I tried all the previously mentioned tricks, and the starter motor still wouldn't operate. So now what?? It sure seems like something is either loose or shorting somewhere in the circuit because it only happens sometimes, but I've checked the wires and connections and everything seems tight.

Should I just start replacing parts of the ignition circuit or can someone lend some light if they've experienced the same problem? If so, where should I start replacing??

Also, how does one go abut checking for voltage to the relay??

I hate to have to replace the the entire ignition circuit system though just to find out that the problem was in the starter motor all along.

Thanks in advance for any advice!

 

Im not sure I completely understood all you did but when I trouble shoot one of these I pull the small push on wire at the relay and connect a test light to it and ground the light. Turn the key to start and if it lights strong then you are good from the IGN switch to there. If you can then jump both large posts together and it will crank then your relay is bad. If not then you have a bad starter, which both the relay and the starter were commonly early failures on the F150. Also check the obvious at the starter for loose wires and connections.