Checking the electric current supply
First control check on a car manufactured after August 1977: is the blade fuse blown?
Placed between the engine compartment and the water tank is this 50A fuse plate (see arrow) in diesel vehicles manufactured after August 1977. Here in the photo you can see: the cover is removed from the small block where the fuse is located. If there are difficulties with starting, you need to check this fuse.
If not burned out, connect an electrical test lamp between ground" and connecting the red-white wire at the glow plug of the 4th cylinder.
Disconnect the wire from the engine temperature sensor (release only after August 1977).
Turn the ignition key to position "Pre-glow"; the control lamp should now flash.
If it burns, then the defect is probably in the glow plugs.
If the light does not light, look for a defect in the pre-glow relay, in the start switch and incandescent switch, or in the central part of the electrical equipment.
Reconnect the motor temperature sensor cable.
Checking the relay and the central part of the electrical equipment
Left: glow plug relay (release before July 1977). Right: construction after August 1977. The newest relay has an additional terminal 50 - this is a distinguishing feature. For the glow plug relay of the quick glow system, the arrangement of contacts is the same as in the right fig.
Connect the clamp of the electrical test lamp to "mass".
With the tip of a test lamp, touch the contact tongue of terminal 30 at the pre-glow relay.
If the lamp does not light up, then the circuit is open: either a break in the wire leading to terminal 30 of the central part of the electrical equipment. or in the central electrical equipment itself.
If the light is on, the problem may be that the relay is not working and. therefore, the current line to the glow plugs via terminal 87 is blocked.
Connect a test lamp to terminal 86 of the relay.
Turn the ignition key to position "Pre-glow".
If the control light is now on, then the wire leading from the starter and glow switch is OK. Then the defect is that the current line from relay terminal 86 to "mass".
Try shunting with an insulated piece of wire.
If this does not help, then the relay is faulty.
In case the light bulb does not flash, the starter switch is damaged or the incandescent (terminal 15), power wire, or the central part of electrical equipment.
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