Engine Won't Crank
 

I'm trying to fix my friends car. The car was driven then shut off and then he tried to start it up it wouldn't even crank. I got access to the starter and discovered there is no power to the starter solenoid when the key is turned to the start position.

I tested the ignition switch and there's 12 volts coming off the switch, I swapped out the gear position switch so i know its not that switch. I tested the voltage at the starter relay and it appears the ground terminal at the relay connector is good, then there's 4.5 volts at another terminal and then 12 volts at the other terminals on the connector where the relay plugs into. The 4.5 volt reading kind of threw me off a little. I'm not sure why its 4.5 volts. Shouldn't it be 12 volts or close to it

I'm not too sure what else to check, I wanted to move the car back his house rather than to keep it in the parking lot so i connected 12 volts to the solenoid and was able to get the car started so it could be moved. He also had a mouse living underneath the hood so I guess its possible the mouse could have chewed through the wire. I'm just stuck and not sure what else I could check. I've been working on this for five days straight.

Before anything else, I'd say remove the mouse. Those aren't good. Now that I have said that, having 4.5 volts on one terminal is okay. What a relay is, basically, is a switch. You use a low-voltage signal to create a higher voltage/amperage current. I would suggest everything you have already done, since you have mentioned the mouse AND it cranks when you hit 12v to the starter, I'd really just say you need to start sifting through every wire you have access to. Not only would you not want to have more electrical issues, but if more stuff has been chewed through, there is a possibility something could start a fire. Which is not fun. Hope this helps!

Kyle