Are R&D parts good

[IDIBRONCO]

so i should only use zd9 glow plugs and no others?

Yes. You'll have to be careful. You can find cheap ones on Ebay and probably Amazon. DO NOT buy those! They are fake copies. They do not last very long. You can buy genuine ones At O'Reilley's or on Rock Auto. There's probably other parts stores that carry genuine ZD9s as well.
If you want to test your glow plugs, unplug the wire from the top of a glow plug. Clip the end of a test light wire onto a positive battery cable. Touch the probe end of the test light to the top of a glow plug. If the light lights up, the glow plug is not burned out.

 

[IDIBOBS]

yes it is on the valve cover what components should i replace in order to get the glow plugs to work is there a way to test of my glow plugs are good? if so how

Yes zd9 motor craft only. They can be had from just about any place. Oriellys autozone Napa Amazon eBay ect….

I personally think the only way to test glow plugs is to use jumper cables and **** direct to the battery and see if they get red hot quickly. I have seen waay to may glow plugs that ohm test fine and are bad.

You’ve got an old truck with some old wiring and some badly done wiring. You’re gonna have to jump in and learn wiring. To me using any glow plug switch is just a band aid to a properly done stock system. Look up a wiring diagram for the glow plug system. Get a test light if not a power probe.

 

[DirtyWood]

ZD29 appears to be the part number for new Motorcraft glowplugs. There also seems to be genuine ZD9 plugs as well but many counterfeits on Ebay/amazon. RockAuto and Oreilly only list ZD29 plugs currently.
When I bought my first IDI the glow plugs were a mess as the previous owner installed Autolite plugs which are known for swelling and being very difficult to remove or worse. If you intend to daily drive this truck I would replace all 8 plugs. Soak the old plugs with PB Blaster or Kroil and then carefully remove them. If a plug is really tight and doesn't want to budge keep soaking it and try to break it free. Once the stuck plug is loose work it back and forth a bit so the lubricant can reach as many threads as possible before continuing to remove it. If any of the individual wires running from the harness to the plugs are broken or frayed they can be easily repaired.
Invest in a decent multimeter since you will need it sooner or later and it's a very useful item in the toolbox.