6.9 tach died

[CaptBuffalo]

My tachometer has no reading at all, it might have happened after I was trying to find a blown fuse and was pulling them out, while the truck was running. I have switched out both the tach itself and the pickup sensor on the injection pump. I also followed the wires from the sensor to the firewall and they look fine. Any suggestions?

Truck is a 1985 f250 XLT lariat 6.9 t19 4x4, in case my signature doesn't show

 

[CaptBuffalo]

I've been reading a bit and one thing people mention is a bad ground, where does the instrument cluster ground out?

 

[Sycostang67]

Have you tried taking the tachometers apart? The tachs in the 80-86 trucks are fairly notorious for failing. If you remove the back and look at the circuit board, there may be a yellow goo covering most of the soldered connections. I guess as time goes by it spreads and becomes somewhat conductive. I cleaned it off and got my tach to work again. I did it with another tach and it worked again for a few months and then quit again. It's a free fix if it works. I think the original purpose of the goo is to help prevent the solder from cracking due to vibration. I'm not entirely sure though, electronics aren't my thing.

 

[CaptBuffalo]

*UPDATE* turns out the fuse was bad, but looked good. However, the tach was erratic once the truck warmed up, so I swapped the sensor and the tach itself with used spares, which didn't fix it, but then I put the original sensor back in and it started to work again. So I don't know exactly what the issue really was, but it seems fixed now.