This smart ***, from this forum say this in 2016

""""""That spark or snap that occurs when connecting a battery is because something electrical is on or running. Interior light, power accesspry or ignition or .....

When that happens a voltage spike is induced into the system. The electronic systems have protection built in for spikes and on some basis when the spike occurs you are testing the protection. The same thing is happening when you "ground the bottom post to the firewall."

In the world called perfect turning off everything so a spike or spark does not occur is the desired result. Can a system survive those kinds of actions? Sure and most of the time the systems do. However in a oft quoted saying, You are playing with fire. Those that play with fire run a greater chance of getting burned.

Use test equipment, wiring diagrams or take the vehicle to a person that has those skills and resources. The original poster fixed his issue when he discovered he incorrectly connected wires. After he discovered the correct routing the engine started. Not saying this is your issue and known the correct wiring is paramount. No one expects any one to know all of the wiring and for that reason a wiring diagram was made. Because mis-wiring ca damage other electrical parts in addition to not solving the original concern.

Or you can continue to attempt repairs with out the resources.""""""""""""""

Well probably will try to rearrange connectors at B+ and if I see spark when try to attach battery + connector will stop again as I did today. Could be it starter on somehow wit my cable setup from B+ to upper post at relay?

 

So went down with voltmeter. With engine off it is 12,5 V at battery. But between upper post at starter relay and positive post at battery is 12,5V to. And is 12,5V between negative post of battery and lower post at relay. It say me that upper post is live to and it do not go to starter positive than to starter negative how much I understand. When did run cord from B+ up to upper relay I brought charge of positive post there and when I did connect negative battery connector I shorted it. Didn't do damage because I did it for split second. Btw when truck is running it is same only with 14,5V.
But see only how carefully they hide schematics for it, same like Manual for pickup. So that you must go to dealer. Not me.
As I understand cable from b+ should go to lower post. But how it if there is alternator cable at lower one. However guy in above link did put positive alternator cable at upper post that is negatively charged (directly connected to negative battery post).
That schematic up, same like one in Hanes, do not worth flying sh.. It say to starter but it do not say to + or - of starter. What f idiots, and they make books about it.

 

Did put new cable to lower post at starter relay and all look good. This morning before fix I had click once and it start in second try. When I put new one on pickup start 5 times at once. So far so good. Didn't check voltage drop, working starting system is check.
Edit. Was planning to be smart so checked voltage around so will not do short. Connected new cable to B+ and than to lower post at relay. Than checked, with + connected, voltage from negative post to negative connector with negative cable disconnected. It was 12V (actually 12,6 like across battery but for simplicity 12V farther). It confused me for a while till I figured out that it should be so as some circuits in truck are alive when truck is off.
Then I checked, with negative cable still disconnected, negative post to upper relay post and than negative to lower relay post. To my surprise both read 12V. I figured out that it have something to do with circuit schematic. So than I tried, carefully, to touch negative connector to post with new cable at lower post now. I get that regular minor spark that you have always when you put negative on.
So connected negative on and checked Voltage between negative and upper at relay and negative and lower at relay. Now negative to upper was 0V and negative to lower was 12V as it was before I add new cable. Started truck and all good as is right now. Didn't recheck voltage drop at positive site. Truck say is ok for now.
Point of this edit is I can not avoid shorting, if something is wrong connected, with checking just voltage right now. Voltage is there all times because of other circuits that work with truck off.
Read little Haynes manual. It say to check starter connect positive post to upper post at relay with jumping cable and it will start starter. When past week I connected new cable from B+ to upper post at relay and than touched negative post with connector I basically tried to jump starter, so I didn't short anything. Only lead battery post is not right place to do it.

 

All good after addition of new cable from B+ to lower post at starter relay. This morning was 56F or so and pickup start right away. Started it during day and yesterday and without any click. Like a bonus digital odometer that work 5% of times now work 75% of times. I did +1. When will get time will do 3 of "3+1".
https://www.f150forum.com/f75/big-3-...ng-how-174540/

 

A few months latter all good with this setup. We had 18F here and truck start like champ. Big 3 is good to know about.

 

It was -10 F or so at Friday and truck started without problem. I still do not understand who the f is hiding key informations about Ford at internet. I had problem to find where wire from B+ go to at relay. A fey yeas go I had problem to figure out proper position of adjustment plate for front struts. Almost nowhere to find it at entire internet. If would be about my small car, Acura, will have same informations in thousands at internet.

 

Edit at 3 sec it shows open circuit at moment and then 3,3V for split second too. It was enough for this sharp-eyed guy to find out what was happening.

 

Man, it is my second-best tread ever. Only after "10 years of cold galvanizing". If ScannerDanner and "South main auto repair" from youtube would see me they would be proud of me.