Well If you think the fuel sending unit is hard to find try finding an aftermarket voltage regulator that works on the '78 Pickup
I tried 3 aftermarket regulators from 2 difference sources and none of them worked on my truck.
After installing them there was no charge light. Yes they all had 6 pins connectors. They were all the same regulator in different boxes.
It all started when my OEM regulator stopped working and I replaced it with a solid state unit from Advanced Auto Parts. With A LIFE TIME GUARANTEE! :-{
I then proceeded to throw the OEM regulator away! I KNOW BETTER THAN THAT. I own a vintage Alfa Romeo and you NEVER throw ANYTHING off that away!
Anyway it lasted less than a year. I went to Advanced Autoparts and they ordered a new aftermarket regulator "free of charge." Really you pay for it and they reimburse you when you bring the defective part back.
BUT, the replacement regulator was a mechanical regulator (HMMM) and didn't work so I tried again. Same story.
So I returned it. no reimbursement for the bad solid state regulator. So I tried NAPA. they give me the the same regulator in a EGLIN Box. It didn't work either.
Out of desperation I try TOYOTA. Ha! They have a re- manufactured OEM regulator on the east coast and it is $7.00 cheaper than the aftermarket one. So I ordered it. It will be here in five days
How's that for making a long story longer :-}
So I have a couple of questions.
First has anyone got a OEM regulator they would be willing to sell. I am an old timer and know the file points and adjust trick. Just to put on the shelf ( The way it is going this truck will outlive me.)
Secondly Has anyone ever put a single wire alternator with internal regulator on their truck and what are the pros and cons and tricks to doing so.
Thanks for your patience
Chuck

 

I have a GM 3wire. Can run it as a single wire. Good investment. Cleans up the engine bay A LOT

 

I’ve used the 6 pin solid state regulator for years with no problems on my 1978.
I believe the mechanical regulators used 5 pin instead of 6 (not 100% sure though).
Check your harness plug for corrosion or bad wires. Check the output voltage of your alternator is sufficient.
It’s rare to have that many new regulators be bad.

 

I have had 2 separate shops test my system and and both test showed the fault is the regulator. 10v output at idle 12 volts output at 1500 rpm and above.
I suspected the alternator at first but both tests showed a bad regulator.
Can any one suggest a source for a one wire alternator for this application?

 

Trail gear has the conversion brackets, and summit has the alternators

 

Thanks

 

Well, the voltage mystery is solved. I now have the OEM VR number from Toyota ( They had to checked the VIN number to get the right one).
Using the OEM part number I went to Rock Auto and found exactly the same low profile VR I have on my truck which crosschecked to the Toyota OEM PN.
The ones that failed to work were high profile and according to Rock Auto do not cross to my OEM Number.
Interesting.
Chuck

 

Hope it works for you. I’ve never heard of high vs low profile VR. 1978 did not have a VIN but a chassis ID number. Post your results when you get the rock auto VR. I’m curious now.

 

That could be on the VIN vs the Chassis number. The Toyota tech was a bit baffled by it being so short.
However, it was listed in their computer.
I am buying the VR fom Toyota but, out of curosity I used Rock Auto as a reference because they show the part number
cross references.
Chuck

 

With 266,000+ miles on it the original alternator is long gone.
The replacement came from Advanced Auto Parts about 10 years ago and has a 3 wire plug directly
into the rear of the alternator. It is a 40 amp alternator.
This worked fine with the original VR until about a year ago. When it died I bought a visually equivalent VR from AAP.
That lasted up until about a couple of months ago.when my charge light began to come on at idle and sometimes as high as 1500-2000 rpm. (see https://www.rockauto.com/en/moreinfo.php?pk=942943&cc=1277108&jsn=368)
When I went to AAP they gave me this (https://www.rockauto.com/en/moreinfo.php?pk=45647&cc=1277108&jsn=369)
The original one was no longer available. When I installed it and the subsequent 2 others none of them showed a charge light when turning on the ignition.
I finally went to the Toyota dealer and explained my problem. He looked it up on the computer and asked for my VIN number.
We went to the truck and he checked the door plate and the underhood plate and finally I gave him My Calif. registration form which shows the chassis number as the VIN.
He went to the computer and came up with a part number: 27700-54040-84. And believe it or not they had one in stock on the east coast.
He showed me the picture and it looks like my OEM VR so I ordered it.
Then I got curious because I had seen the P/N listings on the Rock Auto pages so I went there and lo and behold there was my P/N on the listing for the same VR I have on my truck. (the first one above.) Notice the highth difference on the two.
That's my story and I'am sticking to it ;-}}
Chuck