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1986 Ford F250

I have the mentioned vehicle, with a 6.9L diesel engine, auto transmission… Vehicle has just over 103,000 miles.



The vehicle has experienced this problem 3 times, and I am at my wits end… No one seems to be able to tell me what is wrong…



I start the truck, warm the engine, and when I go to turn the headlights on, all the power cuts off, as though the cables were cut… The first time this happened, I checked all the ground wires… They all appeared okay… I thought, for whatever reason, that it might be the ignition switch… I replaced it, and the power came back…



The vehicle ran for about 3 weeks, and repeated the exact same thing… Engine running, pull the light switch, everything goes dead… I mean everything, as though there were no batteries attached to the vehicle…



I replaced the ignition switch, and the headlight switch, this time, and the power comes back… That was 3 weeks ago…



Last night, out at the store… You guessed it… It happened again… Same way…



There are never any fuses or fusible links blown by this… Ford has no clue… Says they don’t even keep books on the vehicle any more…



PLEASE HELP!!!

When you turn the headlights on, this is like putting the battery under a load test. It sounds like you might have a bad battery.

Tester

Sounds to me like theres a short to ground in your trailer light outlets or wires and its blowing a circuit breaker one of those silver square boxes in your fuse panel or under the hood does it start back up right away ?

If your battery terminals aren’t loose, feel free to check my favorite connection. It’s the ground wire between engine and frame/body, usually to the body on your truck, at the firewall is the usual location. If you see no ground from some metal on the engine to some metal on the body, make one and install it. If there is one, disconnect the body end and wire brush it or scrape it with a knife blade and put it back on. Do replace the negative battery cable if it hasn’t been changed.

i like pleases theory too. My wife said before i typed, battery cable connection but i figured he already checked that. I have a ford 150-79 that seems to run when it wants to how it wants to and it had been in a fire so i wonder if that wire still exists

Hey all… I finally got up enough courage to look at the truck again, and also not want to set it on fire… I’m presently looking at replacing the positive leads form the batteries, but that only goes to the starter… Smaller wires attach to terminals, and go on their merry way…

I have 2 grounds ot the engine… I haven’t found the one from engine to body… Ya may have a point there…

I am able to jump the starter relay and have the engine turn over, but the power is off to the injector pump, so she will not run…

I’m going to check out the ground to the body and get back…

TNX for all the suggestions… Cross yer fingers…

MAC

Okay, we have extra grounds now, from the neg posts to the body… Repaired connections in pos lead to starter, and other batery… Hooked it all up, and no good… Still dead…

I will say that when I go to hook up the batteries, there is a small little “tick” sound, of electricity, and then nothing…

I am feverishly in search of a circuit breaker, or something that is possibly overloaded, cuts out, and resets… But why everything in the entire truck!!!

Headlight switch and ignition switch check out good to go, with a multimeter.

I’m missing something!!!

If you have a good grounding bond between the battery and chassis ground then the next thing to go over is the smaller wires from the positive battery post running to the main power panel under the hood. Check the wire terminals for internal wire corrosion at the battery connection. This is a pretty common problem. If those areas are ok then check the main panel under the hood for a bad connection.

I forgot to mention that older negative cables should be checked for cracked insulation and should be changed if they look ratty. The positive ones are sometimes made with better rubber. To test a negative cable may be easy. Connect a jumper cable to the negative terminal, use both the red and black clamps and connect the other ends to metal on the engine and then try the starter a time or two. If the engine fires up, change the negative cable. This worked on a 73 Maverick.