88 S15 Jimmy Couple of pesky problems

Hey to all,
I have one problem that I've seen others have with newer models, but cant find any info on this one, the other is a minor problem that will just probably take more time than its worth to fix, but I'll mention it just incase....
First, 88 s15 Jimmy 4wd 4.3L V6. The major problem is the 4wd. The transfer case shifts thru all the ranges, 2hi, 4hi, n, 4lo, but the front wheels never engage. I've seen mentions of a vacuum switch located on the transfer case for newer models, but nothing on these. I've even gone so far as to disconnect the cable from the actuator under the battery and manually pull the cable and lock it in place with vice-grips with no luck. I'm thinking that there's some other problem inside the differential or the output shaft clutch, but really have nowhere to start...
This is the first 4wd I've ever had, I've lived in the "Snow Belt" my life and never needed 4wd in the snow, but the added little bit of security in having the 4wd would be nice.

The second little problem is more of an annoyance than a problem, the temperature gauge doesn't work. Never moves off of the bottom pin. I've changed the sensor, but it must be something else....

Thanks for any input anyone can provide. If if you think its nothing, anything will help at this point.......

Greg
SE CT

Just so we start off right...do the front wheels have lock-out hubs that you have to manually engage?

Thanks for responding, but no, there are no hubs. If I remember my GM propaganda right, this was the first year that the 4.3L was available and the one of the first for the "4wd from the cab, no hubs to lock". The only reason I remember that, is because I was in the Navy then, and in early '87 I was shopping for one of these new, but the 4.3L wasn't available yet, and everyone I knew that had one with the 2.8L said it was a dog... I ended up with a C10 Pick-up instead....

Thanks,
Greg

I guess we need to determine where the slippage is or maybe isn't.
If it's in 4WD, high or low, then the motor is shut off & the transmission in Park, the drivers side front wheel raised off the ground (and a jack stand set under the frame so we don't end up with a flat Smokediver) the driveshaft going to the front differential shouldn't be able to turn because the transmission has it locked if the transfer innards are good...right?

The front is locked up the same way the newer ones are, its the same general set-up, with the big difference being the newer ones pretty much all have electronic push -button 4x4. The 4x4 vacuum switch is located on the transfer case, just like the newer ones, but this is not your problem , becasue you bypassed it when you tried using the vise grips to engage the 4x4.

If you actually tried using the vise grips to engage the front diff by pulling the cable and it still didn't lock up, then either you have a internal differential problem, or like chirs steward mentioned, take a look and make sure the front axle is locked when its 4hi or 4lo. If the front axle wont turn, the transfer case is working and locking the front axle. At this point, take a look and make sure your front axles(cv joints) are not broken and allowing the front not to lock up. To do this, raise the front, turn the wheel(s). While turning the wheel, the cv axle should turn together as one piece along with the other wheel too. If this is not the case, then you have an internal problem within the trasfer case. Good Luck