I need help with 1978 GMC wiper problem-Thanks for reading!

[cue1go]

Wipers went out so I tested the motor and the switch connectors for power and both were fine. 4 hots and 2 grounds. I bought a new switch from LMC, Off-low-high only switch. installed and the wipers would only work on low speed in the fast position. The switch that was in the truck was off-low-high only switch also. Traced both grounds and 1 turned out to be the instrument lamp light that only comes on with the headlights so there is only one ground in reality and it went to a good ground. My theory is the truck was originally equipped with a delay wiper switch. At some point in the truck's life that switch went bad and the owner went to a salvage yard or had another truck with an off-low-high only switch and used it instead of the delay switch. This would explain why the wipers would only work on slow in the fast position. The first position on the delay switch is delay, 2nd slow, 3rd fast. The off-low-high only switch 1st position is slow, 2nd fast. Explaining why the 1st/slow position does nothing because it's doesn't have delay and the 2nd position operates at low speed. What do y'all think or does any have any experience with the same problem?

[Migbou]

I have the same issue with my 84, but i have the delay wiper switch with slow and fast. on delay nothing happens, on slow its slow and on fast its slow. I was thinking it was the switch, but if you replaced yours and its doing the same thing i wont bother. it is the original switch that came in the truck. The only thing i noticed was when i remove the motor and moved the Wiper arms by hand they where a bit hard to move, i put so WD40 to try to lube em up but still same thing.. don't know what to try next .

[cue1go]

Your motor is burned up! Change the motor!

[motornut]

my 78 would work sometimes
took it out and noticed the back was pushed out of it
taking it apart found a broken terminal inside
mine has a hole for the light but it dosn't work
and the dirt on the copper strip seems to say never did
i don't think you get delay without a "delay" box
http://67-72chevytrucks.com/vboard/s...=421767&page=3
is mine

84 is it on the coloum?
both will act up when the copper strip that grounds the motor goes green and corrodes
look at the bolts holding the motor ,one has the ground strap
sometimes just turning those bolts a tiny bit will restore the contact if dirty
or make your own ground as a test

[cue1go]

Thanks for the reply but I've done all that and concluded the new switch I bought from LMC was a cheap Taiwanese piece of crap. So I found a Delco and got it headed my way. I tracked down a wiring diagram and verified the wiring on my truck to be of the non-delay type. 5 hots and 1 ground. (Hots-off N/O switch,slow,fast,pump,instrument light) I cleaned the connector the best I could. Every spade was also tightened up because over the years some of them had gotten loose. Got a new wiper motor and it has a grounding strap. I hope this solves my problems.

[Wrecked1982]

if your wipers are too hard to move by hand with the motor disconnected might be the linkage is almost seized