instrument gauges improvement update

As asked, here is an update on fixing the declining gauges of the 89 XJ.

I took the cluster out and inspected the wiring. I cleaned the contacts of the connectors (didnt' really need it) and checked signal levels. The supply was close to battery voltage without loads. I also checked the voltages at the fuse block since almost all of the car supply goes through the key switch - quite a bottleneck. About 0.25v is lost there.

However, the resistance from ground on the cluster to frame ground was 15 ohms! To make the story short, the worst batt ground connection was from the block to the firewall. No cleaning would really improve things, yet there's no rust or such on it. I ran a 10ga wire from the battery to that firewall ground bolt. It resulted in 2 whole volts improvement at the lighter, higher oil pressure readings (20psi hot vs 10psi), and the voltmeter about a volt low instead of 2-3 volts.

The blower motor really takes it down though, so I'm going to probably bring in 4 or 6 ga lines from the battery and feed from that instead of relying on old wiring that's probably marginally rated. The key switch has about 3 or 4 main lines (circuits) it switches to supply the fuse block. I think I'll use those lines to drive relays that will switch in power from these 4ga connections instead. That should get me the extra volt on the gauge and maybe even true oil pressure.

Other benefits from wiring a ground directly to body include better starting - shorter cranking (about a sec less) and when it hits, it's on; faster window motors, and the elec locks seem more reliable - the hatch started working again.

The fuel gauge was always pretty accurate, as seems the temp. Perhaps the sensor levels or design make them less affected.

If I find more I'll write.

Most guage clusters have a voltage regulator to help compensate for varying battery voltage. As yo found that does not work if the ground is crap.

Most do, but 88-90 XJs don't. Got the schematics, verified with the real thing.

BTW, all of the gauge terminals are screwed dirctly to the flex circuit board for contact. I also undid each screw and sprayed cleaner and cleaned each contact point on the board.

Yeah, a bit much, but I was on a mission ;-)

Once a rig gets loaded down with all the power gadgets, 12 Volts is a berely adequate supply. After inspecting my recently purchased 87 XJ, I saw a lot of areas that aren't overbuilt enough to handle all the body electrics. Factory battery cables don't provide near enough wire gauge to the direct body ground, or the B+ lead to the starter relay, and those two leads seem to power just about everything except cranking. Freshen those battery cables up and make them bigger. Go to a truck shop and get some made out of 2/0 and maybe 6 or 4 ga for the smaller leads. Maybe add a second body ground lead and route it along the right fender directly to the firewall. Look at that bundle of fusible links coming off the starter relay, load the circuits and see if you get any loss in any of them. Pull the body ground strap that goes from the engine block to the firewall and check it over real good, or maybe just throw it away and get a shiny new braided strap. Check the adjustment of the ignition switch - the service manual says to mount it with the "off-unlocked" detents synchronized. If you really want to add relays to power the body electrical accessories, don't forget to fuse those circuits close to the source, so these guys :firedevil :firedevil don't get 'ya.