Yes A, B, C and D should always be hot. We were seeing if there is an active short that blows the fuse/wire replacement for the fusible link but it sounds like you can energize everything and the fuse stayed intact. Whats the wire gauge of B? We need to make sure that the fuse value is good, then hook everything together with you temp fuse and we can try to start the truck.


George

 

the fusible link (B) reads 1.0 SQ mm which to me is like reading a foreign language. The test wire (the pesky black wire) is probably 12G, but maybe 10G. It is the same width as the red wires I tested (D and E). Now I don’t know if connecting/testing D and E separately as I did affected the test. Perhaps if D and E were connected to the test wire together would have done it?

The fact that neither D or E blew the 20A fuse in the test wire makes me think it might have just been a corroded wire inside the fusible link. It is very corroded where it attached to the junction block.

 

Then a 20 amp fuse should be good. You can either temporarily connect everything up with the inline fuse or do the complete fusible link repair then try to start the truck.

George

 

with the inline fuse......



SUCCESS!!!

welll at least initially. The truck started after cranking for about 30 seconds, but only stayed on about 10 seconds before it stuttered and shut off and vomited a bunch of gas up out of the barrels of the carburetor.

could be flooding, but to be safe I am letting it sit for a half hour to ventilate.

but feeling the test wire and D and E felt cool to the touch.

 

never mind my previous post...

went to try to restart, not even a click. Thought i’d check the fuse. 20A in-line fuse blown. Whether it was the ignition running through it or that I left the key to run while I dealt with the gasoline, who know.

 

If D is the big red wire on the alternator then the charging current may be blowing the fuse, especially if the battery was not topped off to begin with.

Do you mean liquid gas coming out of the air horn or a vent/gasket leak?


George

 

I had the air filter off, so I could see it coming out of the top of the barrels. It eventually deposited itself on the sides of the carburetor and the top of intake manifold.

that explanation could explain what happened today, but what explains the original blown fusible link when the truck was not even on and all I did was reconnect the battery cable? The original problem seemed a short of some kind. Could that also explain today’s blown fuse? Or are we looking at a different problem?

 

I'll leave the gas flooding alone for now.

The original blown link in an engine that was off and the battery cable connected was most likely a short. The initial fuse experiment was looking for that problem so that you would blow the fuse and not a newly repaired fusible link for diagnosis and then we could further explore the bad leg. Both legs connected to "B" seem OK however. We dont know if the original problem is intermittent or resolved. When the truck starts the charging current may be enough to blow the fuse. Do you have a DC amp clamp meter to see the charging current. A fully charged battery to begin with may prevent this. Another option is a short run with the belt disconnected. Running the alternator electrically disconnected produces nothing but arguments so I have never been able to determine how safe this is across all types of alternators/regulators.


George

 

so, possible explanation for it all....

fusible link corroded and could not handle the 12 V always on junction block, so it burns. Now the battery is a little low 11.93 V stable (with nothing connected) and so alternator tries to step up and throws out more than 20 amps to bring it back up. Which if this is the case, recharging the battery and putting in a correct replacement fusible link should solve the problem.

but before wasting a fusible link on it, I will buy another 20 A fuse, recharge the battery with jumper cables and see if it blows the fuse again.

thoughts?

 

The fusible link blows with current not voltage. Yes I suppose its possible that a damaged link blew with normal current but not as likely in an engine thats turned off unless there is a fault. But possible, yes. I was betting on a shorted alternator diode but the problem did not repeat. The reason I suggested rodents originally is because the truck had just been sitting after a prior successful start. Yes the charging current is higher if the battery is not fully charged to 12.6V. Not sure if the charging current will be high enough to blow the fuse in the initial charge after starting, never measured that first minute or so.


George