Bronco won't start, then puff of white smoke....

Newer bronco owner who has been enjoying the vehicle until last week. Let me start by saying I am new to broncos (and old cars) and learning as I go. Its a stock 1970 with a 302 and 3 speed. I had driven the vehicle multiple times during the day. I went to drive it and upon turning the ignition click (one click) and nothing. My multimeter wasn't reading correct, but it thought lets pull the 9 year old Optima battery and have it checked. After Monument ran a battery and cranking test they said the battery passes. Put it back in and tried cranking. One click nothing. I checked the solenoid. Im able to get current through the solenoid to the starter side. Now I'm thinking it may be the starter. I tried jumping the solenoid and nothing. I pulled a battery from my truck to rule out a bad battery. Nothing. Pulled the starter and hooked it up on the ground from both batteries. It works. Placed it back in vehicle, tried to start, and one click. Nothing. Removed the connections from the front of solenoid for the third time and hooked back up. It fires right up. Drive to Monument for them to run a diagnostic. Test is as follows, State of charge 66%, Battery life 0%, Cranking test 18% at 5.84V and charging system fails. They recommend starting with new alternator and test from there. I install the new alternator, and fires up first try (Now, I wish I would have done a voltage test). Drive it back to Monument for another test. After about 5 minutes of driving, engine dies and white smoke from under the hood. The fusible link wire connected to the solenoid (battery side) melted and broke off between the link and connection lug. Towed home. I don't know were to go from here. I'm thinking of just replacing the battery and starter, but what caused the fusible link to melt and break. Installed a new solenoid and voltage regulator one month prior. Thanks for any advise in advance.

Have you checked your grounds? Replaced battery cables?

Yes, all new battery cables and starter cable. New solenoid and voltage regulator. I detailed the engine compartment a few months ago and cleaned all grounds and replaced the cables.

Since the battery started out low, and not knowing how many amps the new alternator puts out. Is it possible it was putting more amps out and charging the battery at a faster rate than the fusible link could handle?

Also back to the battery ground. Is it grounded to the engine, the frame, the body, or all three. correct answer would be, one way or another, all three. either directly from battery or ground to engine with additional cable from engine to frame and frame to body.

Just because you installed new starter relay and voltage regulator a month ago doesn't mean they are still good especially if china made.

I was thinking the same thing suckerpunched mentioned. Maybe it was charging the battery at to much amperage. In regards to my grounds, it's only on the block. I will take some time and also ground the frame and etc. I still haven't figured out what was causing the original problem of it not starting. We tried working around th battery, solenoid, and starter. Nothing was pointing to a obvious answer. I'm thinking at this point but a new battery and possibly replace the voltage regulator and solenoid. I also need to figure out what size fusible link. Napa has them listed by wire size, not amps. I think the wire diagram calls for a 38A fuse wire.

half cab said:

Just because you installed new starter relay and voltage regulator a month ago doesn't mean they are still good especially if china made.

Click to expand...

My last voltage regulator was broken right out of the box. Made in China.

keep in mind the solenoid needs a ground to work. a coil is energized which takes a + & - creating a magnetic field that pulls the contacts together. Usually the mounting screw is a sufficient ground but paint and corrosion could affect it. just removing and re installing could fix it if it's that. but the body needs a good ground too.

After some time today digging through the alternator harness, I found a frayed open wire that shorted out. I have a new alternator harness on order. I will check all grounds and add to frame and body. Still not sure what the original cause of th vehicle not starting was.

On another note, does anyone know the correct size fusible link to buy? I've seen in previous posts and my 1970 shop Manuel mentions a 16g. I found a chart that said 16g is only good for 16-20amps. The wiring diagram calls for 38A.

The body ground to negative battery post is a very important ground. With out the proper body ground, the starter solenoid, the voltage regulator and all the dash functions don't work properly. Make sure the mounting bolts for the starter solenoid and voltage regulator are on clean steel for proper grounding. This goes for the headlights, turn signal lights and the horn too.

Well the problem seemed to point back to a bad voltage regulator I just replaced one month ago. I ended up replacing the alternator and battery. I think in the process of changing out the alternator I may have damaged a wire in the alternator wiring harness that shorted out on the exhaust manifold causing the fusible link to burn up. Once that was fixed, and with the old battery and alternator replaced, I ended up buying a new voltage regulator. It runs perfect for now. At least Napa swapped out the bad regulator. Thanks for the advice on the voltage regulator Half Cab and Broncojunkie, I would of never expected that to be the problem.