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
Air-core meter driver
Yeppers. I solved Gary Lewis' tach reading too high in just a couple minutes time. His was a DS3 - DS2 conversion.
Near the DS2 box is a connector with 2 wires, 1 green, 1 black. The green wire goes to the coil, and the black wire goes to ground, but ONLY on a V8 truck. A factory 6 cyl truck will not have the black wire on the engine side of that plug.
As for the crud inside the tach causing erratic behaviour, these trucks are not the only ones that suffer from the issue. I need to disassemble the tach in my RX7 and clean it up. It works fine, till the temp drops to under 40F. I rarely remember about, since I rarely drive the car in temps cool enough to cause the tach to "wig out".......
Would you happen to know off hand where the ground wire from this plug attaches?
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.
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
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.