So yesterday I was doing my last adjustments to my weber carb and timing but then I started to have a problem.

When I turn off the key, the lights in the cluster dim slowly and the engine stays running for around 35 seconds then shuts off. The reason why I think it stays running is when I turn the key off there is still enough power for the coil and to activate the fuel pump relay until the voltage drops too low to keep the engine runing then the relay clicks off.

I am sure it is not dieseling, the weber is nicely tuned on the lower circuit, plugs look good and when I turn the key off, I can really see the lights slowly dim in the instrument cluster until they turn off.

Anybody had that problem here? I hope it is not ignition switch related, can anyone point me in a direction of what to check with a multimeter? Grounds are all new or clean. Thanks!!

 

Hate to say I'd suspect the ignition switch first. Find and disconnect the plug set for that switch and start testing it with the multi-meter.
- If that 100% not it, start hunting for a hot wire thats shorting to another wire. You have a real mystery there, as i cant think of anything that would make an old truck act like that...... what year is your truck?

 

Thanks for the reply batousaii, it is a 1981 that I have completely disassembled and reassembled with some new or improved parts and some of the old original parts. For the wiring, everything has been running really good electrical-wise since the last week (first time I started it) and checked all fuses, etc. all seemed to go well.

As for electrical modifications I have spliced the 12v ignition switch wire for the radiator fan controller and the fuel pump relay, all was done cleanly, soldered, heatshrinked and taped but I will go through that again. Unplugging the switch and testing each wire for voltage drops or anything not normal will at least isolate the problem to the switch or the rest of the wiring I guess, thanks for the tip.

Why now truck needs to be ready in 18 days!

 

Oh man, I hear ya. My wife went to Japan to visit family, and a week after she leaves (three months ago) my engine blows a piston and cracks the sleeve. So, I scrape up all my extra cash and get a rebuilt engine. All goes well,,, for 100 miles... then it blows the transmission. I again, scrape up cash and get a rebuilt L52 transmission. I plan to install it on Tues/Wed this week, and my wife returns from Japan on the 23rd (15 days). It's our daily driver... I been living on my motorcycle rain or shine the whole while. It's been three months of mechanical hell.

- I'm right there with ya buddy! Have a beer! We'll make it!

Edit to add:
Hmmm, take a pen and paper and draw/map out exactly how you did those electrical mods so you can visually scrutinize it. I am wondering if you may have inadvertanly wired in a secondary power supply to the coil thats kept live until the radiator's fan controller switch breaks circuit. If the circuts are direct from battery, circumventing the ignition switch, then your fan's temp switch may be acting as a secondary on/off where only one needs to be on to supply power, but both need to be off to remove power. Cant say why the lights would dim out slowly, . It is very odd, almost like some capacitor is retaning enough electricity to keep things on for a little bit until depleated, or maybe the fan is somehow acting as a generator when the power circut is removed and it free spins for a few seconds feeding power back through the line? <thinking>
- Double check it... a pen and paper combined with some multi-meter time under the dash and hood might solve your problem.
- Have you tried disconnecting the thermo fan switch and see if it shuts off the engine durring it's mystery minute? Just an idea

Bat.

 

That would be a good idea to try to isolate the fan from being the problem. Tomorrow I'm going there with a multimeter and I will first try to clean and lube the ignition switch to see if it's not sticking inside, then I'll do some diagnosing. Thanks for the help and a beer to you too! We always make it haha

 

Just curious if you got anywhere with this? I was also thinking about it, and it might be prudent to run a relay with the electric fan setup.

 

Well I haven't really got the truck running because of other problems and things I need to work on at the moment, but so far just by playing with the key on/off it hasn't done it again. It will run again maybe sunday or next monday so I'll keep you updated.