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Changed my battery/alternator about 45 days ago. Running perfectly then I noticed the Gen light stayed on after starting the truck up and it died after about 20 seconds.Truck will start on a dime, even after sitting for 24 hours after the last start, but will only run for 20 or so seconds and die out. I tried changing the coil, coil is not the issue. Any ideas? I feel like the fuel pump could be the issue here since I do not hear the pump start when the key is in the on position, BUT this does not explain why my generator light is on and I feel like I would waste my time changing the fuel pump if there is another problem before it. Any suggestions would be well appreciated!

Check your Voltage Regulator?

On the 6 wire plug from the VR white red = W = fuel pump and charge light, white = W = ignition, white blue = B = battery, black = E = earth, British for ground, white black = F = field, the stem of the Tee connector to the alternator, and white green = N feeds back to the VR.

LUV's have a weak link in the electrical system, the fusebox. The terminals the wires connect are riveted to the fuse holders. A little age and corrosion, and you get electrical intermittents. I solved mine by taking it apart and soldering the joints. Others have cleaned it with lemon juice, and others a new fuse box.

When the generator is working, you should have 7 volts on the white green wire to the VR. It should then apply 14 volts to the white red wire turning off the ''C'' light and activating the coil of the fuel pump relay under the cover by the firewall on the passenger's side. Alternator no workie, fuel pump no workie. Check everything else before replacing the VR. A couple of years ago I think went through 3 alternators from AAP before getting one that worked.

Labman did an excellent job of explaining one of the Luv's pitfalls, the extreme wiring going to the fuel pump. The engine runs for about 20 seconds because when the starter solenoid is energized the fuel pump relay is also activated, but just while the key is turned to start position. This is why a lot of guys cut into the fuel pump wire at the fuel pump relay and run it to a keyed 12V scource. This way if the alternator ceases to function you can still drive the truck, at least until you can fix the charging problem. And tapping into the fuel pump wire does not affect anything else, For safety you could also install a oil pressure switch so the fuel pump won't work until oil pressure is up. It is also a necessary item if you ever go to a one wire alternator, then you eliminate the entire voltage regulator and wiring going to it.
Good luck, dp

Here is a tip for all: If the alternator ever dies and the fuel pump stops and the truck dies. Just unplug the voltage regulator plug and you can drive on home. It goes like this--When you unplug the regulator you take the load off the white/red wire that also feeds the generator warning light. This will now provide current through the warning light bulb to operate the fuel pump relay. Complicated I know but it realy works and can get you home instead of stuck on the side of the road.

Great tip Egg. I have a switch wired to the battery to directly run the fuel pump. Mostly it allows me to pump a little gas out of the truck when I need some for my chain saw or something. It got me home a few times too.

Thanks for all the VERY helpful responses guys. I was set that it was my alternator but it passed the test at carquest with flying colors. It was mentioned that the fuel pump will activate in the on position but we all know the sound of the LUVs fuel pump starting up and even in the On position it does not activate. So here's what im stuck with...Generator light stays on, alternator is perfectly fine, fuel pump does not activate. Im really leaning towards an issue in the wiring or fuse box. What should be my next plan of attack?

I think the alternator can charge without putting out the 7 volt signal to the white/green wire. Also, the VR could fail to give 14 volts to the white/red wire. I would check for those voltages.

Do the fuse box fix. Remove it, dremel off the rivets, clean the buss bars, and pop rivet back together.
My generator light was coming on, and it was the fuse box and nothing else. Cheap easy fix and it eliminates a likely source.

HomeGrown76Luv I got distracted checking and changing everything else and it turned out to be the voltage regulator. First reply to my post and that was the solution! I owe you one. Thankyou everyone else for providing me with helpful tips for my next issue

Anytime, glad to help~

The last fuse box I did I just put the entire box in a bin of lemon juice. No disassembly. After it was shiny I sprayed the lemon juice off with contact cleaner. Worked great.

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1978 LUV Custom - 1979 LUV stock

I soldered the contacts together 5-10 years ago and mine hasn't missed a beat since.

I thought about just soldering them, but I guess I wanted to stay semi original if possible. I forgot to mention that I also replaced the terminals on the wires that connect to the fuse box.

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1978 LUV Custom - 1979 LUV stock