If somebody was working on the top end of the engine it could be the glow plug controller was disconnected. The ground wire on the GPC is very important.
I replaced one glow plug (Motorcraft only) and at the same time cleaned the ground that goes to the engine from the GPC and it really improved my glow plug cycling. 87s have the newer 7.3 GPC.
It previously was on for a few seconds and then cycled rapidly. After cleaning the ground, it is on for 10 to 15 seconds and cycles much slower.
Then I cleaned the positive battery cable junction and the engine whirs right over and starts great.
I replaced one glow plug (Motorcraft only) and at the same time cleaned the ground that goes to the engine from the GPC and it really improved my glow plug cycling. 87s have the newer 7.3 GPC.
It previously was on for a few seconds and then cycled rapidly. After cleaning the ground, it is on for 10 to 15 seconds and cycles much slower.
Then I cleaned the positive battery cable junction and the engine whirs right over and starts great.