I'm shopping around to replace the gauge cluster in my 1991 SR5 Pickup. It seems that cable driven speedos were used in 89-92 and then electronic VSS was used in 93-94.1995 4Runners went back to cable driven speedos, however those clusters have a weird PCB piggybacked to the back of the instrument cluster with three wires running to it. Does anyone know what this thing is?

I'm thinking of grabbing one to see if it will work in my truck (the late model cable driven clusters are more plentiful with lower mileage/wear than earlier versions like in my truck), and it appears it should, but I haven't been able to find a 1995 pinout to compare it to a 1991 pinout to see what the differences are and I don't know what this mystery component is. At first I thought it was some kind of alarm or buzzer tied into one of the idiot lights but now I don't know.

I have a 1992 Factory Service Manual but the cluster there appears to be slightly different.

Here's what the cluster looks like in my truck


1991 V6 Pickup cluster


Here's a cluster from a 1995 V6 4Runner


1995 V6 4Runner cluster with piggyback

 

Update- it looks that mystery thing is the “bulb check relay”. I’m guessing it’s what illuminates all the warning bulbs in the cluster at startup so you can ensure nothing has burned out.

As far as whether the 1995 4runner clusters will work in an earlier cable driven truck, we shall see.

 

One more update - besides noticing I am an idiot and can't spell component in the title of this post, I can confirm the late/95 style cable instrument clusters with the bulb check relay are indeed plug and play with earlier cable drive units.
I pulled my cluster out and put in one that came out of a 1995 4Runner and everything works as it should. Actually works better than the one that was in my truck (speedo in mine was worn out and bouncy, and would scream when cold even after replacing the speedo cable).