Glow Plug Relay 300 TDT

Can the glow plug relay become partially defective, or is an all or none type of part?
I could not get my '82 300 TDT to start. I replaced the battery and
the glow plugs and it was still starting hard. I noticed that if I counted to 15 after the glow plug light in the instrument panel went out before I try to start the engine starts normally.
It seems that either the relay is taking longer to get the plugs hot or that it is turning off the light before it should. I took the cover off the relay and watched the contacts, and they stay closed a lot longer than the light stays on. The light is staying on about a count of 7, and I add 15 to that, so I wait about a count of 22 before turning the engine over and it starts good then.
Should I replace the relay? And if I do, should I replace it with an OEM type or one of those Bosch ones that stay on three minutes? I just put in a set of Beru glow plugs.
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One thing that you might want to remember, depending where you are, its getting cold. The valves are metal and contract. So do all of the parts that help keep them at the correct settings. SO is it possible that the valves need to be loosened up? I have noticed that the relay runs longer than the light to. I let mine go until I see the dash light get a tad bit brighter ( less load on he battery) and then crank.
Good luck. I would leave the relay alone and check the valve clearance.
Bill
1984 300D Turbo with Auto Xmission and about 190,000 miles.

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Traditionally you are supposed to change your relay along with your plugs.
Now about your plugs... are the new one needle points or loop style. If it is loop, then most likely relay or the glow plug fuse. If your plugs are needle points, you are supposed to run a parallel circuits to make it work.
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