R700 gauges do not work

[beatngu]

Well some of my gauges do not work on the wrecker. I do have oil pressure voltmeter, air pressure and speedometer. My temperature, tach and fuel gauge does not work. not too worried about the fuel gauge as that one should be a simple fix. I do not know where anything hooks up on the old detroit for these gauges, can't find a diagram or schematic by far. My tach and speedo are integrated, and this motor may not be original to the truck any ideas?

[mrsmackpaul]

are these electric gauges if so might just have a crook ground common to the gauges that arent working

Paul

[phildirt]

The R model wiring diagrams are posted in the wiki section of this web site- R-Model Wiring Diagram -

It is a good place to start.

The tachometer is mechanical.

[beatngu]

I have seen 2 of the mechanical gauge cables in the engine compartment but can not find the hook up anywhere on the engine for it, would it be on the transmission? Fuller RTO 15 speed

[j_martell]

Mechanical tach will read from the motor, old macks is on the front of the pump, i dont know shit about detroits....except they supposedly might leak some oil lol , mechanical speedo will read from the output of the transmission.

[gearhead204]

the detroits could hook the tack drive about anywhere look on the rear of the engine about centerline of the eng. above the bell housing. or on the front or off the blower possibly. as for the temp gauge napa sells a long sender mechanical gauge, look around where the upper rad. hoses connect to the eng. that should be in the area of the thermostat housings and then you should be able to find a port to use. for the temp sender (remember to double check that the probe has enough room to not be damaged.)as for the fuel gauge touch the insulated wire to the ground wire at the fuel tank sender if gauge goes to full replace the sender, if not check gauge the same way if it checks out look for damaged harness.

[b68]

On ‎11‎/‎22‎/‎2014 at 1:11 PM, beatngu said:

Well some of my gauges do not work on the wrecker. I do have oil pressure voltmeter, air pressure and speedometer. My temperature, tach and fuel gauge does not work. not too worried about the fuel gauge as that one should be a simple fix. I do not know where anything hooks up on the old detroit for these gauges, can't find a diagram or schematic by far. My tach and speedo are integrated, and this motor may not be original to the truck any ideas?

check for a wire from the hot lead on the starter up to the buss bar on the fire wall

[m16ty]

I don't know if this is your problem but my electric gauges in my RD822 would work sometimes and sometimes wouldn't. Come to find out it was the main solenoid behind the dash that was sometimes loosing connection.

 

I found a make and model number on a tag on the solenoid. Come to find out the solenoid's main application is in HVAC systems. Ended up ordering one off Amazon for a fraction of the cost of one from Mack.