85 j10 instrument cluster gauges not working

[wcprejean]

Hey guys, this is my first post, have an 85 J10 I6 trying to get roadworthy and struggling to get gauges working , have cluster out and get good continuity from sending units to gauge, getting voltage to red wire in cluster harness but no power to any of the gauges? am i assuming correctly if i test each gauge ,i should get 12 v at one of the connectors at back of gauge? thanks in advance!
Bill P

[BCRAWLER]

Coolant temp guage also has voltage regulator that drops the voltage to 5 volts for the feed to the guages. On this forum you will find many post on how to swap it out for a 7805 transistor. Hopefully this helps.

[wcprejean]

update on cluster, thanks for the tip Bcrawler! yep my cvr was bad on coolant gauge, replaced with one from BJS, all good now, interesting tip though , the gauges will peg out if you are holding instrument cluster in your hand and its not grounded to frame! attach a ground from metal backing of instrument panel to any close by grounding spot
thanks again guys

[tgreese]

The built-in voltage regulator (CVR) will not regulate without a ground. No ground, full voltage to the gauges, gauges peg. Risky for the gauges.

Removing this behavior forms a significant advantage to the 7805 solution. WIth the silicon chip regulator (7805 or 7806 or equivalent), the regulator circuit is open with no ground. Then voltage to the gauges goes to zero.

[wcprejean]

thanks! i will look into that before i reassemble dash

[DARREN LILLY]

Can you do the 7805 swap to a guage that is already faulty

[tgreese]

Can you do the 7805 swap to a guage that is already faulty

Depends. The temp gauge has both the CVR and the gauge in the same housing, with 4 connections total, including ground through the case. If the CVR is broken but the gauge is ok, you can fix it by adding the 7805 as a voltage regulator. If the gauge part is broken, there's no saving it.

The fuel gauge is just the gauge, and either it works or not. It also takes the regulated voltage from the temp gauge, so that has to be working before you can condemn the fuel gauge.

[letank]

the good link:

http://www.fsjnetwork.com/forum/viewtop ... =10&t=8334

basically you shunt the oem wires in the back of the cluster and add the transistors gizmo:





a lot easier than trying to retrofit a latter cluster with the vacuum controlled aircon controls and the dash fittings