No start need help/big puff of smoke

[Michael Star]

Ok, my 1970 GMC 350 went to start this morning and it tried to crank over. It started to catch then everything died. I saw a big puff of smoke from under the hood and I popped it to find the fuseable link on the firewall closest to the battery had gone. Bought new cables (both pos and neg) and put them on. Checked all fuses under the dash and they look fine. I can't find any other fuseable links except that one near the dist block on the fenderwell. I have no power to anything and I cannot figure it out!!

[MARKDTN]

Do you have a wiring diagram? Do you have power at the alternator post? How about at the horn relay?

[Michael Star]

Have power at alt, nothing at horn

[Michael Star]

I've got it narrowed down to something shorting out when I turn the key to start it, but I can't figure out what.

[68gmsee]

Since I'm not sure exactly where the problem is I can only suggest that I usually start by disconnecting as many associated wires as possible and then reconnect one at a time until the failure occurs. The last one reconnected is the culprit.

I would try disconnecting the coil/hei/voltage regulator/alternator wires and see if the fuse blows.

You can find the electrical diagrams in the electrical section FAQ section.

[Michael Star]

Disconnected both the alt (someone converted it to an internal reg) and the coil but it still blows. Checked all the wiring under the hood and there are no cuts/abrasions. What gets me is that it doesn't blow when I try to start it, only when I turn it to on. I can turn on the lights/wipers and honk the horn and it is fine.

Also, what amp is the fuseable link that is next to the battery? My next step is to go into the cab and inspect the ignition. Any other ideas?

[68gmsee]

Originally Posted by Michael Star

.... What gets me is that it doesn't blow when I try to start it, only when I turn it to on.....

Also, what amp is the fuseable link that is next to the battery? My next step is to go into the cab and inspect the ignition. Any other ideas?

Confused. You have to turn the key to on first to start it.

Anyway, I'd replace the ignition switch. It may be internally shorted.

[red71cheyenne]

And there were two fusible links. They are both 4 amp and located at the fenders on both sides. Black wires with a sort of bulb in the middle of it. You can buy fusible link at most auto parts stores and just replace both to be safe.

Check to make sure your shift lever is really in park or neutral, this will give a false indication of no power to the starting ckt. And like 68 said, I'd check the ignition switch too.

[Michael Star]

Just got done checking out the ign switch. Just for good measure I bought a replacement one. Some of the insulation was coming off the wires so I just taped them for now, but still no go.

[Michael Star]

Finally traced it to the highbeam foot switch grounding out...