Test Glow Plug Relay and Timer

[7and2]

Sounds like a I have a possible common problem with my New Holland TC29D. When I turn the ignition switch fully to Acc/Run the glow plug light seldom if ever comes on and the tractor is slow in starting when weather gets cool thus I believe the glow plugs are not functioning. I replaced the glow plugs with no change. Other than being a "parts changer" what is the method/procedure to test the ignition switch, glow plug relay and the glow plug timer with a digital VOM? I would rather test the possible failing parts than replace all of them if not necessary.
Thank you

 

[jaxs]

One at a time in no particular order and may as well check other circuits while the meter is handy.

 

[oldnslo]

Do you have the electrical schematic for that tractor? If yes then use the VOM to verify voltage going through the switch to the relay. Next verify relay is changing state and that voltage is being supplied to the glow plugs. Timer should time out and shut relay off.

Remove wire to glow plug and check resistance of each glow plug. They should be similar from one plug to the next.

Not sure what amperage the glow plugs draw so I would be careful trying to check amp draw with standard VOM.

 

[WranglerX]

Simple test to see if power is getting to glow plug buss would be to just use simple test lamp, probe to buss, clip to ground and turn switch to either glow plug position or start if test light illuminates glow plug circuit is good, if not start tracing back with probe till you find voltage, trouble will be pretty close to where you lose the voltage...Having wiring diagram will help you trace the glow plug circuit and find the problem....

 

[nyone]

I believe the power comes through the ignition circuit. Check for burnt or discolored terminals at your key switch first. Then do a visual check on all the plugs before even useing a test light.