Tach dies when idling if brakes, heater, etc are turned on...

[Mini-Stroke...]

Ok, the truck is an 87 ranger with the 2.3L Diesel, 4x4 5spd tranny.
Problem is that any time the truck is running if I turn on the heater the tach dies, turn signals- tach bounces, headlights- tach dies, all of these problems are at idle. But then if I'm cruising and turn the heater on full blast the tach jumps UP about 500rpms (engine speed does not change)

My question is, what is causing this? I have already changed out the little voltage regulator on the back of the gauge but that did not help any.

Any help is greatly appreciated.

 

[Mini-Stroke...]

Any ideas, or does anyone have a gauge cluster wiring diagram?

 

[7.5L_STX]

id buy an aftermarket tach, thats just me though. i hate messing with electrical lol.

 

[Earl43P]

I'm gonna GUESS that a diesel tachometer has to be using some kind of hall effect sensor (magnetic pickup, senses pulses as metal interrupter passes by). Those are low voltage frequency pulses, so the instrument cluster may be quite different for the diesel. I don't know.

I suggest you clean up the major grounds in the engine compartment, on the fenders, radiator support and firewall. The tach might share a ground point with lights / blower.

 

[Mini-Stroke...]

Thanks for the input, also, I did some looking under the hood today and noticed that there is a ground lug on the engine block but no cable coming from it.... could this affect it any?

 

[Earl43P]

Absolutely could.

Typical Ford truck grounds are Bat- to radiator support (small wire), Bat- to frame then engine block (big wire). Aftermarket replacement cables sometimes omit the frame connection.

Firewall (wiper motor bolt) to cylinder head.

Grounds for lights and fuel pump are on the fender, under the hood, should find 3 or 4 of those, total.

 

[Mini-Stroke...]

Thanks, I will have one made up tomorrow and report back with the results