If you are shopping to buy a Tachometer look for the newer style that has an IC chip and less parts. There is not a cover over the back, It comes out of the cluster just as shown.
This was taken out of an 1986 F150.
.

 

Interesting, I never seen that kinda of tach on these year of trucks. If possible what is the numbers that are on the IC chip? Its just out of focus to read it.

 

LM1819 Air-Core Meter Driver
General Description Features
The LM1819 is a function generator driver for air-core
(moving-magnet) meter movements A Norton amplifier and
an NPN transistor are included on chip for signal condition-
ing as required Driver outputs are self-centering and devel-
op g 4 5V swing at 20 mA Better than 2% linearity is guar-
anteed over a full 305-degree operating range


Self-centering 20 mA outputs
12V operation
Norton amplifier
Function generator
Applications

Air-core meter driver
Tachometers
Ruggedized instruments

 

Would you happen to know off hand where the ground wire from this plug attaches?
Thanks

 

The end of this ground wire, the point where it touches metal, is in side the Dist Cap.

This wire is also the sole point of ground for the entire in IGN system. So if the engine runs ... the ground wire is good.

Not really sure if this answers your question or not.

Jim

 

Thank you for your reply

 

Did this to my tach last weekend - worked great - now reads like it should and doesn't change readings at will. Note instead of the the q-tips I used a very soft old worn out toothbrush and it seemed to work nicely. Thanks for this tip.

 

Hey fellas,

I have an Australian 1983 f100xlt 351c. I will be taking the in instrument panel/gauges out again as my Tacho is not working,and will post a picture of the rear circuitry . Ive read that the 1980 models in the US have a green circuit on the back and from 1981 on it changed to red. Well maybe we just got old stock over here. They tell me that the ones over here were a Canadian build etc . So I will send yall a pic

Cheers

 

I just wanted to revive this thread to assure members that this thread is worth its weight in gold. This past weekend, while at the 2016 OK-GTG, the tachometer in my 1986 F150 was taken out and cleaned as detailed on page #2 of this thread and it worked as described! Thanks to Gary Lewis for his "hands on" assistance!

The inside of mine was no where near as "bad" as the one shown in this thread, but the tachometer still was not performing properly and after the cleaning, it reads correctly, again.

The symptoms of my truck's tachometer was this: it read 50+% high. It was as though both the 6 cyl. and 8 cyl. circuits were both being activated? Anyway, after cleaning, the tachometer is working beautifully.

 

David - You are welcome. It was fun. And productive, although I had my doubts. That's because your tach looked clean to me. Even the Q-Tip we used on it only had a little bit of yellow, but apparently it was just enough to cause problems.

I'm glad it is now working for you.

 

Hi, old thread, I know but...
if you are going to do this be careful when doing the top of pcb (where all the components are). There is a rheostat (adjustable resistor) on the bottom left (on mine anyway) that you don't want to turn. I Believe it may be used for calibration of the tachometer, don't know for sure but try not to let it turn anyway. Better safe than sorry.

Sully

 

Necro post I know, but wanted to add to this discussion. My Tach on my '81 150 4.9 4speed (Srod), had a tach that would only work on really cold mornings until there was some heat in the cab. Then go dead. I checked the wiring from the ds2 to the tach, green with some color trace, ohmed out to tach. With truck running had 12v to tach, good ground and a fluctuating voltage on other pin. Don't remember the label.

I took the instrument cluster out and found tach had cover, 2 Phillips head screws and four brass nuts with washers holding it together. disassembled, and found the ground contact pin loose when tach tightened. There is a post that the underneath of the circuit board touches to provide ground to coils for the tach. added solder to raise the height of the post, and reassembled, tach now works fine.

I am located in E. TN. and it was in the upper 40's today. Sorry I didn't take any pictures otherwise I would have been more specific as to details.

LNK