1986 Bronco with 300 L6 and four speed. It sat for some time before I bought it, so I recently replaced the battery. The starter worked perfectly initially, but after a couple of weeks (it's a weekend driver at best for now...) it got to where it didn't want to crank. Put on new battery cables and a relay and still no joy. Busted out the jumper cables and she cranked right over then roared to life.

Battery shows 12v when sitting, 12v when running, and craters when I try to start. My first thought was to replace the alternator - and I'll probably end up pulling it and having it tested anyway. NAPA has the alternator harnesses and fusible links/wire, so I figure it's worth $18 to ensure the problem isn't there.

Other than that, what else should I check?

And on a related note, could a bad alternator/harness also cause the gauges (other than the tach), brake lights, head lights, etc. not to work?

Thanks.

 

12 volts when running means the battery is not being charged. One thing you can try is take a voltmeter or testlight, and make sure you have 12 volts on the large bat output lug on the alternator when the engine is off. If you don't, you probably have a bad fusible link.

 

The battery definitely needed a charge. The trickle charger was laboring away @ ~10 amps when I first hooked it up. The alternator tested out okay. As I was removing the alternator to have it tested I noticed the belt was looser than it should have been. That may have been the source of my charging problem. A wee bit shorter belt will fix that.

But...

I checked continuity on all the harness wires with a test lamp and they passed. Previous owner had mangled the wiring a bit - the wire going to the choke (white/black) had been cut. Someone just stripped off ~ 1 inch of insulation from the middle of the green/red wire, spliced it in, and taped it up. The green/red wire also had a spot where the insulation had been rubbed through near the alt. harness; the 10 ga. yellow wire to the same harness had a couple of breaks in the insulation as well. I replaced them both, spliced the choke wire back where it belongs and taped the harness back up. Now I just need a couple of days of decent weather to button everything back up.

After removing the power steering belt and A/C belt so I can slip on a new alternator belt, that is. What a pain...