Hey guys I've been working on my '87 Ford F250 460. I gather a lot of great parts from junkyards. I never like the original cluster. It doesn't have tach. I found cluster with tach off the '88. Turn out the tach was broken, it spin wild and redlined going 45 mph which i know it's not redlining. Found other tach off the 1991. Tach works but the battery was broken, it went side to side like on crack. Got another one from other 1991 (exchanged for another one so I don't shell out $$) Everything finally works and I'm satisfied. However I noticed something and maybe you guys can help me out.

My original cluster and '88 oil pressure gauge works, accurate reads. But I noticed 2 1991 clusters oil gauge doesn't move at all. I know the last one i took off the oil gauage works. But not on my '87. I reinstall the '88 cluster, oil gauge read correctly. Then I reinstall the '91. No reading.. What's up?? Thanks guys!

Oh btw, the junkyard that I scored was great condition for its age if anyone interested knowing, It all came off from 1991 and 1992 Ford F250. Those are;
frame, cab, bed, bumper, rear leaf springs with brackets, coil, arms, arms brackets, gas tank, tailgate, and radios. I love the 1992 cab because it has rear speakers and better seat belt setup (from shoulder to hip, my '87 are from hip to hip ya know?) I plan to swap and 87 supercab slant windows (side windows) will fit '92 side windows.

 

If you ground the connecter at the sending unit does the gauge peg high? Possibly sending unit changed from '87 to '91.

 

The earlier trucks had a sending unit that reported pressure as a variable. No pressure, some pressure and high pressure and all points in between. The cluster had no resistor in the pressure wire and trace. The system shows pressure varying with rpm.

The later trucks had an on/off sender. It was all the way on or all the way off. The matching cluster had a resistor on the pressure trace. The needle is at the bottom or in the middle. This system is a glorified idiot light that looks like a gauge.

The sending unit must match the gauge cluster (not the gauge itself). You have a variable sender with an on/off cluster. You have two choices: put in an '87 or '88 cluster; or put a jumper wire over the pressure resistor on the back of the cluster.

I have written a thread on "upgrading" the later trucks to the earlier system. Look for that. It is a popular upgrade for the later trucks. There are probably several writeups on that. You can see a picture of the resistor to be jumpered in one of those threads. It is VERY simple.

I'll try to find a pic Wednesday night if you can't find one.

 

put up pic i'm very interested in that. I'll look for your old thread.

 

I could not find the pics of my tach cluster. I just moved to a new computer.

I took two pics of my '89 low end cluster (Later style with resistor). My tach cluster is installed in the truck.

The first is of the back of the cluster. The second is a close-up of the upper left corner of the cluster.

The highlighted area shows the oil pressure trace, resistor and connector to the op gauge (silver metal square with hole in the middle). Solder a jumper wire across the resistor leads to bypass it. Don't solder the circuit board. Be quick and have a light touch. I would use a small soldering pencil not a soldering gun.

To find the resistor on the high end tach cluster, find the gauge connector to the op gauge. It will have the gauge post poking through from the op gauge. The trace to that connector will have a resistor on it.

 

I wanna give update;

The cluster I got from junkyard, 1990 Ford F250 works great. It is plug and play. Very easy swap. Everything works except oil pressure. I haven't decided if I want roll the miles to match original. (118,000+ miles original and this cluster is 98,000+ miles) It's nice to have tach now.

Make sure cluster comes from same motor. For example I didn't realize the first time i took cluster was f150 with inline 6. While driving 45 mph, my tach was over 6k which i know it's not.. Went back to junkyard and realize it was f150. Look around and found 1990 F250 that has 460. Took it out and install on my 250. now my tach are in right reading, going 2k rpm at 65.