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A few days ago my 85' f350 w/7.5 wouldn't start. I saw smoke coming from under my dash. There's a blue/red wire going from my ignition switch, to I think the fuse box. This wire is melting every time I turn the key to start
. What would be the cause of this, and how do I fix it? All my fuses are good. I changed my starter and solenoid.
A few days ago my 85' f350 w/7.5 wouldn't start. I saw smoke coming from under my dash. There's a blue/red wire going from my ignition switch, to I think the fuse box. This wire is melting every time I turn the key to start.
What would be the cause of this, and how do I fix it? All my fuses are good. I changed my starter and solenoid.
That looks like wire 32, as seen on pages 26 and 30 here:
Wire 32 provides power to actuate the big starter relay, and also signals the DuraSpark module when Start is commanded.
First thing would be to unhook the wire from the start relay. This should be the red wire with a blue stripe on the small terminal on the starter relay. Also disconnect the connectors at the ignition module. If not already unhooked, remove the connector from the ignition switch, too.
That should leave wire 32 totally isolated. Use an ohmmeter to check for any continuity to ground. There should be no continuity at all. Any continuity indicates a bare spot touching ground. That alone would cause a huge current flow and melt the insulation.
Give that entire wire run a good visual inspection in case it has melted to an adjacent wire.
If the isolated wire checks good, next I'd completely disconnect the starter solenoid. Remove the small wire 32, the big cables, and any fusible links. Leave it bolted in place for a good ground. Set your meter to DC amps. Make sure the meter is capable of handling at least 10 amps. Put the meter's (+) lead on the battery's (+) terminal. Put the (-) lead on the small relay terminal where wire 32 was. The relay should make a big clunk and the meter should show how much the coil of the relay is drawing.
Let us know what the meter shows. I don't have a maximum spec for amperage draw, but maybe somebody else can chime in.
This wire does not go to the fuse box. It leaves the ignition switch and goes through the firewall to a connector underneath the brake booster area. If you have a automatic, it continues down to the side of the transmission to the neutral start switch. It can get in harms way down here, especially if the exhaust has been modified. From there it comes back up and goes over to the starter solenoid like the other poster mentioned, to trigger the starter to turn.
If you have a manual tranny it leaves the ignition switch and goes through a clutch switch up high on the inside of the firewall, and then it also goes out to a connector under the booster, but then there is a jumper there and it continues to the starter solenoid since a manual does not have a neutral safety.
