13BT pre-heater light

[jblueridge]

The Pre-heater light no longer comes on in my '88 BJ74. I took the dash apart and found it is not a burnt bulb. Bulb works fine when wired up directly.
I get a reading of 24V on one of the wires when the ignition is turned on but the light won't light.

I checked my FSM wiring diagram but I am not sure if it is wired the same way as glow plugs on say a 60 series. I could not find a Pre-heater light in the diagram.

Where should I look next?

 

[carpet]

The screen only comes on at low temps, try taking the temp gauge out, this forces the screen to come on. You can hear the solenoid switch on. If it come on and still no light you have another problem. Also there is another plug near the terminals on the glow screen. this one is disconnected to test how long the afterglow stays on for.

 

[jblueridge]

Thanks Carpet.
I guess I need to read up on where these devices physically are.

 

[John Galt]

, try taking the temp gauge out, this forces the screen to come on. ....

All you need to do is unplug the connection to the temperature sensor in the t-stat housing. Nothing needs to be taken out.
The single wire connection is for the temp gauge, the two wire connection is for the glow control.

 

[jblueridge]

Okay; I can find the t-stat housing well enough.
I'll try it.

 

[jblueridge]

I unplugged the temp sensor, half destroying the brittle plastic and wire clip on it.
Plugged in, no light at 50 deg. F, 10 deg. C.
With the sensor unplugged the light comes on.

Sensor is bad?

 

[John Galt]

Plugged in, no light at 50 deg. F, 10 deg. C.
With the sensor unplugged the light comes on.

That indicates normal operation. On the 13B-T the temp sensor turns the pre-heat glow-screen off 3°C above freezing. The diagram above in msg#2 is for the 3B glow plug system, not the 13B-T glow screen shown here:

The simplest manual override is to insert a normally closed push button switch in the temp sensor circuit to momentarily disconnect the temp sensor when pre-heat is wanted above freezing temps.

more at

Super Glow - explained

 

[jblueridge]

Thanks for the info!