This one has me scratching my head.

Swapped my bad 3.5L 603-970 with a good 3.0L 603-960 engine from an '87 300TD. I having issues with the glow plugs.

I've checked the system as told to by All-DATA and the FSM, all seems good.

At the relay I get 12.4VDC to each pin going to the glow plugs when the relay pulls in. Checking at the glow plugs with the relay pulled in I get 0 VDC. The leads check out has having 0 ohms resistance. As the glow plugs have <1 ohns this does not surprise me, there is no potential across the glow plugs.

I pulled the lead of #6 as it easy to get to. With the relay pulled in all I get is 5.5 VDC.

Is the issue the 603-960 glow plugs with a 603-970 glow plug relay?

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1988 300SE 83K+
1991 350SDL 283K+