engine control fuse blows

[Middle man]

Just retired carpenter. I've followed this forum for some time now. Because of the helpfull tone,not punishing I just joined. And I need help! I have a datsun fiberglass sunrader camper,32k miles. It sat for 30 yrs,cause of a death in the family. It has the l20b engine. I installed a weber carb, new dizzy,all new vaccum hoses,water pump,battery,fuel pump.all new filters and fluids through out. the local shop replaced the front end, rubber bushings were rotted. No matter what power source I've tried this fuse blows. Check wires with meter, connections all seem to be fine. Replaced relay at end of fuse box to no avail. Emissions system was all removed before i owned it. It will run all day in the drive way without fuse blowing, one mile down the road it blows. It removes the power from the electric choke,when the fuse blows. Thanks for any direction you can offer! Chuck

[datzenmike]

Sounds like a wire is pinched and driving probably grounds it and the fuse blows. I'll check when I get home to see if there is anything else on that fuse that could cause this or would be affected by leaving it blown. Often it's something that been added like a radio of fog lamps.

 

If nothing is affected you can simply unplug the choke relay and jumper the Blue choke heater wire on the carb to the Red idle cut solenoid beside it. This just ignores the  blown fuse and get power for the electric choke from somewhere else.

[Middle man]

Thank you for your response. After asking every auto shop and mechanic I know, no one seems to know what that fuse controls. Also after reading another post, I realize that I don't have an idle cut solenoid on my carb. I also forgot to mention its a 1980 model. But I did try another power source and it still blew the fuse. idk...

[Middle man]

Well for what its worth, I found out today the fuse in my 720 blows when I shift into 4th gear. The fuse would even blow in the driveway with just key on! I went under to see if any wires were cut or not connected to the transmission. Disconnected the backup lamp switch and the fuse worked fine. I get it the previous owner did replace the tail lights,with out back up lights. My guess there's an open circuit towards the rear of the vehicle. What I don't get is, why 4th and not reverse when it blows? Also tranny knob rattles and growls,need advice on best tranny oil? I have royal purple syn. 75w-90 in there now, any advice apreciated.

[datzenmike]

My guess is the reverse light wires are on the top gear switch on the transmission.

 

 

The reverse lamp switch is just to the rear of the clutch arm and boot on the passenger side of the transmission about half way up the side. Or it's the switch closest to the front of the vehicle. The correct reverse lamp switch wires are...Yellow/Red stripe and Yellow/Blue stripe.

[Middle man]

After much research...Mike I hate to ask but what the hell is a top gear switch and what is its purpose? Do I even need it? Also after reading tranny posts, I'am convinced I need to change my universal joints and center bearing to eliminate the chatter in the shifter. It rained all day,and I did'nt feel like laying in the water,tomorrow I'll check the wiring again but I do know one of 2 dark wires broke away from one switch. The 2 yellow wires were attached to the switch next to it. I replaced all the cabinets,plumbing,frig. and added a/c, I gotta get out of town I'am gettin to old for this shit! Thanks in advance

[datzenmike]

It's emissions related. Tells the truck that you are (probably) at highway speeds. The '80 had a fuel shut off system using the idle cut solenoid. If you think about it, when you let off the gas on the highway it is still sucking in the idle mixture gas even though it isn't needs or doing anything but going out the tailpipe. If conditions are right the idle cut is turned off to save the gas and reduce  emissions.

[Middle man]

Thanks Mike,soon as I figure out which switch is which I'll hook it up and I'am gone! Gonna order some new rear lites I found and install them whenever we return. I got to learn to post pictures,I'am a good carpenter and proud of my interior. But I have alot to learn about mechanics...ugh!

[datzenmike]

The reverse lamp switch is just to the rear of the clutch arm and boot on the passenger side of the transmission about half way up the side. Or it's the switch closest to the front of the vehicle. The correct reverse lamp switch wires are...Yellow/Red stripe and Yellow/Blue stripe.

[Middle man]

After cleaning the wires and being able to see thier colors,I could tell they were crossed. The switches both had only one correct wire on each.Paired them up together [ as suggested ] and it all works now! Without blowing the engine control fuse,DAMN...Thanks Mike it was driving me nuts. I notice there's another switch above the speedo,and my book says its for the o.d. that  sound  right? cause as far as i know i don't have that option. Without the correct colors I don't think I could have got it right!

[datzenmike]

Not all transmissions have these but in addition to reverse...

 

There is a neutral switch up just forward of the sifter near the top.

A top gear or over drive switch lower down