Gauges reading low. ICVR?

[Rembrant]

My three gauges are all reading low. I noticed the other day that all three were dead, as in all hard to the left well below zero. Today, they are working again, but all reading low. Wondering if I should start with new senders or swap out the ICVR first?
I can test temp and Oil pressure by touching them to ground ya?

[Gary Lewis]

If all three are doing it the common denominator is the ICVR.  I'd order the adjustable voltage regulator and make those puppies reliable.

And yes, you can test by touching the sender wire to ground.  But if the ICVR is working at all it'll usually peg the gauge even if it is wonky.

[Rembrant]

Gary,
Where is the instrument cluster grounded do you know?

[Gary Lewis]

Yes, I do know.  But it took some sleuthing to prove it.

The proof is here.  On Page 87 you'll see that Pin 2 of C208A, which is the connector for the gauge cluster, is Circuit 57 and that it is grounded at G701.  And on Page 88 you'll see that G701 is "behind instrument panel near right hand side of radio".

[Rembrant]

Swapped the ICVR today and no change, so I grabbed a new coolant temp sender and installed it but haven’t tested yet. Swapped the gauges too and they seem fine. Both oil and coolant gauges peg hard to the right when grounded. More to come.

[Lima Delta]

Is it usual for the ICVR to suffer intermittent issues, or is it more common for it to just fail outright?

[Gary Lewis]

I've not seen an ICVR completely fail.  But I have seen them all of a sudden give different readings on all three gauges, only to go back to the previous reading in a bit.  However, I can see that they could fail if the contact points in them fail to make as they close.

I really like the true voltage regulator I have on Big Blue.  My gauges are rock solid and never flinch.  So while I scan all the gauges frequently I feel comfortable with the stock gauges now.

[Rembrant]

Update: I swapped the ICVR with another one and no change. I installed a new coolant temp sender and cleaned up the connections and it is now working great. I cleaned up the connections for the oil pressure sender it is is ok, but reading a little low (I doubt it is the gauge’s fault, but I might swap the sender anyway).

However, I noticed today that the gauges were all dead and at the lowest point below zero when I was first driving but they all started working again a little while later. Odd. I did have to boost the truck though, the battery was dead because I forgot the key on the other day.

[Gary Lewis]

Sounds like a bad connection in the circuit to the ICVR.  Maybe at the gauge cluster?

[1986F150Six]

Cory, if the ignition switch is sticking, the gauges will not work. When this happens, see if the turn signals work? Jiggle the ignition key.

[Rembrant]

1986F150Six wrote

Cory, if the ignition switch is sticking, the gauges will not work. When this happens, see if the turn signals work? Jiggle the ignition key.

David,

Excellent internet diagnostics! My ignition switch actually IS sticking. Sometimes it stays too far forward after starting, and my signal lights will not work. I try to remember to turn it back, but sometimes forget. I betcha that is the problem. I will check and reply back. Thank you sir!